WBBSE Class 10 Life Science Solutions Chapter 3A Heredity

Detailed explanations in West Bengal Board Class 10 Life Science Book Solutions Chapter 3A Heredity offer valuable context and analysis.

WBBSE Class 10 Life Science Chapter 3A Question Answer – Heredity

Short answer type questions : 2 Marks

Question 1.
Define heredity. Give some common instances of inherited traits in Humans.
Answer:
Heredity may be defined as the transmission of characteristics through generations. Common instances of inherited traits may include, colour of skin, colour of eyes, diseases like, diabetes and conditions like baldness.

Question 2.
Name the two laws of inheritance postulated by Mendel?
Answer:
1. The Law of Segregation
2. The law of Independent Assortment

Question 3.
How do Mendel’s experiments show that traits mav be dominant or recessive?
Answer:
Mendel took one tall pea (TT) plant and one short pea (tt) plant and produced progeny from them. The plants grown from F₁ seeds represent first filial (F₁) generation. All F₁ plants were tall. Then Mendel self-pollinated F₁ plants and found that all plants obtained in F₂ progeny were not tall. Instead 75% were tall (dominant) while remaining 25% were dwarf (recessive traits). From the experiment, he concluded the F₁ progeny is not a true breed but carries both traits. He concluded one trait is dominant over the other, that’s why plants appear tall. It is also called the law of Segregation.

Question 4.
How do Mendel’s experiments show that traits are inherited independentily?
Answer:
When a pea plant of round green (RRyy) seeds is crossed with a pea plant having wrinkled yellow seeds (rrYY), plants in F₁ progeny have round and yellow seeds. However in F₂ generation, all traits appear independently. In F₂, he got the following result (called dihybrid ratio):
Round Yellow-9
Wrinkled Yellow – 3
Round Green – 3
Wrinkled Green – 1
He concluded alleles controlling different traits are not linked and are inherited independently. It is also known as Law of Independent Assortment.

Question 5.
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enoagh to tell you which of the traits-blood group A or O – is dominant? Why or why not?
Answer:
No, the information is not sufficient. The blood group is determined by a pair of genes. It might happen the gene responsible for O group in the daughter might be inherited from mother or from father. For example, one possibility is father having AO pair and mother has O O pair of genes.

Question 6.
Define allelomorph.
Answer:
The contrasting pair of genes or alleles constitute an allelomorph. Examples : Tall and dwarf plants, wrinkled and smooth seed coat, white and violet coloured flower.

Question 7.
How is the sex of the child determined in human beings?
Answer:
Normal human somatic cells are diploid. They have 46 chromosomes made up of two sets of 23-one set from each parent. In human diploid cells, there are 22 homologous pairs of autosomes, each with a maternal and a paternal homolog. The 23rd pair, the sex chromosomes, determines whether the person is female (XX) or male (XY). Mother provides only X chromosomes. The sex of the child is determined by the type of chromosome (X or Y) received from male gamete.

Question 8.
Define Homozygous.
Answer:
An organism that has a pair of identical alleles for a character is said to be homozygous for the gene controlling that character. Homozygous plants “breed true” because all of their gametes contain the same allele-either TT or t t for example.

Question 9.
Define Heterozygous.
Answer:
An organism that has two different alleles for a gene is said to be heterozygous for that gene. Unlike homozygotes, heterozygotes are not true-breeding because they produce gametes with different alleles; for example T t.

Question 10.
A normal pea plant bearing coloured flowers suddenly start producing white flowers. What could be the possible cause?
Answer:
Because of change in genetic sequence (called mutation).

Question 11.
What is mutation?
Answer:
Organisms have evolved in number of ways to protect their DNA from changes. In spite of these mechanisms, however, changes in the DNA occasionally do occur. Any change in the DNA sequence is called a mutation. Mutations can be caused by errors in replication, transcription, cell division, or by external agents. e.g. nuclear radiation can lead to mutation.

Question 12.
Why are human beings who look so different from each other in terms of size, colour and looks, said to belong to the same species?
Answer:
Although human beings look so different from each other in terms of size, colour and looks, but all of them belong to same species (Homo sapiens) because of the following reasons:

1. All human beings belong to same species and are able to interbreed.
2. Fossil evidences prove that Archaic Homo sapiens arose in South Africa and moved across continents and developed into distinct races during the ice age.
3. Fossil evidence shows that humans have not changed much anatomically over the last 200000 years.

Question 13.
If the sperm bearing Y-chromosome fertilizes the egg, the child born will not be entirely like his father. Why is it so?
Answer:
It is because the other sex chromosome i.e. X-chromosome also has its effect on the fertilized egg.

Question 14.
A normal girl baby receives her X chromosomes from which?
Answer:
Both from her mother and father (One X from father and another X from mother).

Question 15.
List the seven pairs of contrasting characters or traits selected by Mendel while doing experiment on garden sweet pea (Pisum sativum).
Answer:
seven pairs of contrasting characters or traits of garden sweet pea (Pisum sativum):

Traits α Characters	Dominant	Recessive
1. Form of Seed	Round(R)	Wrinkle(r)
2. Colour of Seed Coats	Coloured(C)	White(w)
3. Colour of Cotyledons	Yellow(Y)	Green(y)
4. Colour of pod	Green(G)	Yellow(g)
5. Form of Pod	Inflated(I)	Constricted(c)
6. Position of flower	Axial(A)	Terminal(a)
7. Height of Plant	Tall(T)	Dwarf(t)

Question 16.
Define gene. What are its important characteristics?
Answer:
Gene is the unit of inheritance.
1. Genes are found in chromosomes at fixed positions.
2. Each gene is responsible for a providing particular trait to an organism.
3. Chemically gene is a segment of a large polynucleotide molecule called DNA (deoxy-ribonucleic acid) and RNA (ribonucleic acid)

Question 17.
Who was Gregor Mendel and what was his contribution to science?
Answer:
Gregor Mendel was an Austrian monk who first started the study of inheritance in an organized manner. This was the beginning of genetics and therefore, he is called the Father of Genetics.

Question 18.
Which plant did Mendel select for his studies and why?
Answer:
Mendel selected the purebred garden pea plant for his studies. These plants showed many contrasting traits that were easy to track through the generations. These plants are naturally self-pollinated, allowed him to easily get pure lines for his studies.

Question 19.
What are hybrids? How does one distinguish a monohybrid from a dihybrid cross?
Answer:
The plants produced as a result of cross between two different plants are called hybrids. Monohybrid cross is the cross between two organisms in which the inheritance of only one trait is followed. The crosses that study two traits together are called the dihybrid crosses.

Question 20.
What are phenotype and genotype?
Answer:
Phenotype refers to the externally exhibited trait, whereas genotype refers to the traits developed by genes.

Question 21.
What is the physical basis of heredity? What are alleles?
Answer:
Genes are the physical basis of heredity. The different expressions of the same genes are called alleles.

Question 22.
What are homozygous and heterozygous plants?
Answer:
Homozygous plants are those with similar alleles for a trait. Heterozygous plants have different alleles for a trait.

Question 23.
What are the phenotypic and genotypic ratio in the F₂ generation in monohybrid cross?
Answer:
The phenotypic ratio in the F₂ generation in monohybrid cross is 3 : 1 and the genotypic ratio is 1 : 2 : 1.

Question 24.
Which are the allelic forms of the gene for height?
Answer:
The two allelic forms of the gene for height are T, the dominant gene for tallness and t, the recessive gene for dwarfness.

Question 25.
What is the law of unit characters?
Answer:
According to the law of unit characters, all the traits are separate entities or units by themselves whose inheritance is controlled by factors, now called genes.

Question 26.
Where are genes present and what are they made up of?
Answer:
Genes are present arranged in a linear manner on the chromosomes. They are made up of series of nucleotides in a particular sequence.

Question 27.
Which are the two types of chromosomes and what is the difference between them?
Answer:
The two types of chromosomes are : autosomes and sex chromosomes. While autosomes have homologous chromosomes as pairs, sex chromosomes are of two different types – X and Y.

Question 28.
How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
The trait which appears in all the members of F₁ generation and also in 75% numbers of F₂ generation obtained by self fertilization of F₁ generation is dominant character.
The trait which does not appear in F₁ generation but after self-fertilization of F₁ generation, reappears in 25% of F₂ generation is known as recessive.

Question 29.
How do Mendel’s experiments show that traits are inherited independently?
Answer:
Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of F₁ generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F₁ yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded , 3 short round seeded and 1 short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only when the traits are inherited independently.

Question 30.
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits- blood group A or O – is dominant? Why or why not?
Answer:
No. This information is not sufficient to determine which of the traits – blood group A or O – is dominant. This is because we do not know about the blood group of all the progeny.
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.

Question 31.
A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer:
This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

Question 32.
Outline a project which aims to find the dominant coat colour in dogs.
Answer:
Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog.

A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.
Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb).

In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.

If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb) and 25% homozygous brown (bb) offsprings.

Question 33.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes. All human chromosomes are not paired. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome.

During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in formation of the diploid zygote. The zygote in the progeny receives an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.

Question 34.
Guineapig having black colour when crossed with guineapig having same colour produced 80 offsprings, out of which 60 were black and 20 were white. Now find out : (a) What is the possible genotype of the guineapigs? (b) Which trait is dominant and which trait is recessive? (c) What is this cross called as and what is its phenotypic ratio?
Answer:
(a) Bb × Bb
(b) Black is dominant and white is recessive.
(c) Monohybrid cross, phenotypic ratio = 3 : 1

Question 35.
Why did Mendel choose pea plant for his experiments?
Answer:
Mendel chose pea plant for his experiments because it is
(a) Easy to grow.
(b) Short lifespan.
(c) Easily distinguishable characters.
(d) Larger size of flower.
(e) Self-pollinated.

Question 36.
What do you mean by genotype?
Answer:
The complete set of genes in an organism’s genome is called genotype.

Question 37.
What do you mean by phenotype?
Answer:
The observable characters in an organism make the phenotype. Phenotype is a result of genotype’s interaction with the environment. Due to this reason, many phenotypes are not inheritable.

Question 38.
What are the possible reasons of pea plants used by Mendel?
Answer:
Pea can be termed as biennial plant, i.e. two generations of a pea plant can grow in a given year. This means that Mendel could get enough time to observe a larger number of generations.

• Many easily identifiable and contrasting characters are present in pea plants.
• Cross pollination can be easily induced in pea plants.

Question 39.
State the Law of Independent Assortment.
Answer:
Mendel’s Second Law : Law of Independent Assortment : Alleles of different characters separate independent from each other during gamete formation.

Question 40.
What do you mean by sex determination in human?
Answer:
Somatic cells in human beings contain 23 pairs of chromosomes. Out of them the 23 rd pair is composed of different types of chromosomes, which are named as X and Y chromosomes. The 23 rd pair contains one X and one Y chromosome in a male. On the other hand, the 23rd pair in a female contains X chromosomes. This means that all the eggs would have X chromosome as the 23 rd chromosome, while a sperm may have either X or Y chromosome as the 23 rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote would develop into a female child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote would develop into a male child.

Question 41.
What are the components of chromosome?
Answer:
Each chromosome is double or replicated and consists of two thread like structures called chromatids attached to each other at centromere. Each chromatid has a number of dense areas arranged linearly, which are known as chromomeres. They represent the areas of active genes. Internally each chromosome has two spirally coiled threads called chromonemata embedded in matrix. These are DNA molecules.

Question 42.
How is sex determined in human beings?
Answer:
Sex is determined at the time of fertilization and the two sexes are produced in approximately equal numbers. A human male has XY sex-chromosomes and produces two types of sperms (heterogametic). Either with X-chromosome or with Ychromosome.
A human female has XX sex-chromosomes and produces ova of one type (homogametic) all with X-chromosomes.

Long Answer Type Questions : 5 Marks

Question 1.
What do mean by heredity and variation?
Answer:
The offsprings of all the organisms (plants and animals) resemble their parents in several aspects. This is only due to the phenomenon of heredity. Hereditary literally means “tendency of like begets like” i.e. all living organisms tend to produce offsprings like themselves.

Hereditary may be defined as the transmission of characters from one generation to successive generations or from parents to their offsprings. Thus, heredity is the cause of similarities between the offsprings, so that the individuals of the same parents resemble each other in many aspects. Heredity involves the transfer of genetic characters from parents to the offsprings via the egg and sperm. These transferable characters are called “hereditary characters”.

Variation : Though offsprings receive all the characters from their parents, they are not exactly alike. Differences are found even between the offsprings of the same parents. It is difficult to find out the identical individuals. The progeny differs not only in itself but also with the parents. These differences are called variations. Thus, variations may be defined as the visible differences between the parents and the offsprings or between the offsprings of the same parents.

Question 2.
Describe different types of Variation.
Answer:
The variations may be classified into two types:
i. Hereditary variation : The variations which arise as a result of any change in the structure and function of the gene and are inherited from one generation to another are called hereditary variation.

ii. Environmental variations : Two individuals with the same genotype may become different in phenotype when they come in contact with different conditions of food, temperature, light, humidity and other external factors. Such differences among organisms of similar heredity are known as environmental variation. These are not heritable.

Based on the type of cells, variation is classified into two types.
i. Somatic variation : The variation which occurs in somatic cells is called somatic variation. It is generally insignificant, because it is not inherited from parents. It is acquired by the organisms during their own lifetime and is lost with death. Hence, it is also called acquired variation.

ii. Germinal variation : The variation which affects the germinal or reproductive cells is called germinal variation. It is heritable and genetically significant. It provides raw materials for evolution.

Based on the degree of differences, variation is classified into two types:
i. Continuous variation : Small and indistinct variations are called continuous variation.
(a) These are fluctuating with environmental conditions.
(b) These are non-heritable.
(c) They have no role in evolution.
(d) They are most common and occur in all organisms.

ii. Discontinuous variation : Large, distinct and sudden variations are called discontinuous variation.
(a) These are relatively unaffected by environmental conditions.
(b) These are heritable.
(c) They provide raw materials for evolution on which selection is based.
(d) They are not common and appear suddenly.

Question 3.
How is the sex of the child determined in human beings?
Answer:

In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.

The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes : 22+X Or 22+Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
Type of female gamete : 22+X
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.

Question 4.
Explain Mendel’s experiment of monohybrid cross on pea plant?
Answer:
Mendel selected for his experiment two types of bisexual sweet pea plants-one tall pure plant and one dwarf pure plant. Each tall and dwarf plants are made true breading by self pollination. These true breeding tall and dwarf plants are called parent plants and the generation is known as parental generation. First and second filial generations are arranged through cross pollination and fertilization among the hybrid plants.

T = gene for tallness of pea plant
t = gene for dwarfness of pea plant
T, t = genes are alleles for each other
T = gene is dominant over t gene

Cross pollination performed among all hybrid plants produced during first filial generation.

F₂ generation is shown through checker board or Punnet square

Phenotype : Tall pea plant : Dwarf pea plant = 3 : 1
Genotype : TT : Tt : tt = 1 : 2 : 1
Explantion : In monohybrid cross, hybrid pea plant is produced at the first filial generation. There is no dwarf plant in this generation. But at the second filial generation, there is 25% dwarf plant. Dwarfness character is again developed at the second generation.

When in a homologous chromosome pair a pair of contrasting characters are present in a cross, the contrasting characters never get blended but they separate out during gamete formation in the next generation. This is known as Law of Segregation or First Law of Mendel.

Question 5.
Explain Mendel’s experiment on dihybrid cross with the help of two pairs of characters in pea plant.
Answer:
Mendel selected bisexual pea plant for dihybrid cross. He has separated one pea plant with pure, smooth, yellow seeded pea plant and one pea plant with pure, winkle, green needed pea plant.
R = gene for smooth seeded character.
r = gene for wrinkle seeded character.
Y = gene for yellow coloured seed.
y = gene for green coloured seed.
R, r are both alleles and R gene is dominant over r gene.
Y, y are both alleles and Y gene is dominant over y gene.

Phenotype : 100% pea plant with smooth, yellow coloured seed.
Genotype : Hybrid plant (Heterozygous)
Cross pollination is performed among all hybrid plants produced during first filial generation.

F₂ generation is shown through checker board or Punnet square

Explanation : In the first filial generation, hybrid plants with smooth yellow seeds are developed. Four types of gamete are produced in this generation. Any gamete is fused with any other type of gametes to form sixteen types of plants.

When two or more pairs of contrasting characteristics present in a pair of homologous chromosomes are involved in a cross, segregation of one pair of characters is independent that of the others and one can fuse any of the others independently. This is known as Law of Independent Assortment or, Second Law of Mendel.

Question 6.
Explanation : Mendel’s monohybrid cross in guineapig.
Answer:
Pure black coloured hair and pure white coloured hair are selected, when monohybrid cross is experimented in case of guineapig. Gene for black colour hair (B) is dominant over gene for white colour hairs (b). Both B, b genes are both allele.

Phenotype : 100 % guineapig with black coloured hair.
Genotype : Hybrid guineapig (Heterozygous)
Sexual reproduction is performed among all hybrids produced during first filial generation.

F₂ generation is shown through the checker board or punnet square

Phenotype : Black coloured hair : White coloured hair
= 3 : 1
Genotype : BB : Bb bb
= 1 : 2 : 1

Explanation : Recessive characters-white coloured hair of guineapig remain suppressed in the first filial generation. Dominant character is expressed. But in the second generation, the recessive character is segregated separately. This is the Law of Segregation.

Question 7.
Explain dihybrid cross with the help of two pairs of characters present in guinea pig.
Answer:
Two type of guinea pigs are selected for dihybrid cross guinea pig with rough (RR) and black coloured (BB) hair is crossed with smoth (rr), white coloured (bb) guinea pig.
B = gene for black coloured hair.
b = gene for white coloured hair.
B, b are both alleles; B gene is dominant over b gene.
R = gene for rough hair
r = gene for smooth hair.
R, r are both alleles; R gene is dominant over r gene.

Phenotype : 100% rough, black coloured guinea pig.
Genotype : Hybrid guinea pig (Heterozygous)
Sexual reproduction is performed among all hybrid guinea pigs produced in the first filial generation.

F₂ generation is shown through checker board or Punnet square

Explanation : In the first filial generation, hybrid guineapigs with rough, black colour are producted. Gametes developed from the male and female hybrid guineapigs. Any gamete are fused with other type of other gametes to form sixteen types of guineapigs. This is the Law of Independent Assortment or Second Law of Mendel.

Question 8.
What is incomplete dominance? Explain it with an example.
Answer:
Incomplete dominance : It is the deviation of Mendel’s law of heredity. When pure homozygous dominant alleles are crossed with pure homozygous recessive allele, the heterozygous hybrids are produced during first generation, with a few phenotypic character. The phenotypic character is not the dominant but near to the dominant character. It is known as incomplete dominance, e.g. when homozygous dominants red flowered 4 o’ clock plant (Mirabilis jalapa) is crossed with homozygous recessive flower plant, the heterozygous plant with pink colour flowers are developed in the first filial generation. The homozygous recessive characters become reappeared in the next generation without blending each other.

F₂ generation is shown through checker board or Punnet square. Cross pollination among the plants of F₁ generation develops two type of gametes

Phenotype : Red flower : Pink flower : White Flower
= 1 : 2 : 1
Genotype : RR : Rr : rr = 1 : 2 : 1
Explanation : Dominant character i.e. red colour is not expressed in the F₁ generation but new character, the pink coloured flower is developed. The dominant and recessive character with the new character are again expressed in the F₁ generation. It is the deviation of Mendel’s law. The phenotype and genotypic ratios are not same as Mendel’s experiment.

Multiple Choice Questions : 1 Mark

Question 1.
Alternative form of gene are called ________.
(a) Loci
(b) Multiples
(c) Chromosomes
(d) Alleles
Answer:
(d) Alleles

Question 2.
Heredity or inheritance of specific traits became clearer due to
(a) Lamarck’s theory
(b) Mendel worked on garden peas
(c) Darwinism
(d) Neo-Darwinism
Answer:
(b) Mendel worked on garden peas

Question 3.
Which of these is homozygous recessive?
(a) Ss
(b) ss
(c) SS
(d) s
Answer:
(b) ss

Question 4.
What will be the genotypic ratio of the cross between Rr and rr ?
(a) 1 : 2 : 1
(b) 3 : 1
(c) 1 : 1
(d) 1 : 1 : 1
Answer:
(c) 1 : 1

Question 5.
What will be the genotypic ratio of the cross between Rr and Rr ?
(a) 1 : 1
(b) 3 : 1
(c) 1 : 2 : 1
(d) 1 : 1 : 1
Answer:
(c) 1 : 2 : 1

Question 6.
The offspring resulting from a cross between two pure homozygous recessives would be ________.
(a) 50% homozygous recessive and 50% homozygous dominant
(b) 75% homozygous recessive and 25% heterozygous dominant
(c) 75% homozygous recessive and 25% homozygous dominant
(d) 100% homozygous recessive
Answer:
(d) 100% homozygous recessive

Question 7.
On what cellular structures are genes in eukaryotes carried?
(a) Endoplasmic reticulum
(b) Nuclear membrane
(c) Chromosomes
(d) Mitochondria
Answer:
(c) Chromosomes

Question 8.
In man the chromosome number is 46. How many chromosomes are present in man’s muscle cells?
(a) 23
(b) 46
(c) 96
(d) variable
Answer:
(b) 46

Question 9.
The component of a chromosome that controls heredity is ________.
(a) proteins
(b) histones
(c) DNA
(d) RNA
Answer:
(c) DNA

Question 10.
Number of chromosomes in a human male is ________.
(a) 23
(b) 23 pairs
(c) 22 pairs +XY
(d) 22 pairs
Answer:
(c) 22 pairs +XY

Question 11.
In dogs the chromosome number is 78 . How many chromosomes are present in the dog sperm?
(a) 78
(b) 39
(c) cannot determine from this information
(d) variable
Answer:
(a) 78

Question 12.
Homologous chromosomes which are similar in both the sexes are called ________.
(a) sex chromosomes
(b) autosomes
(c) allosomes
(d) androsomes
Answer:
(b) autosomes

Question 13.
How many pairs of contrasting characters of pea were selected by Mendel for cross fertilization?
(a) six
(b) seven
(c) five
(d) twelve
Answer:
(b) seven

Question 14.
RrYy yield gamete of which type?
(a) four
(b) five
(c) two
(d) six
Answer:
(a) four

Question 15.
Genetic information is carried out by long chain of molecules made up of :
(a) phosphates
(b) MRNA
(c) nucleotides
(d) none of these
Answer:
(c) nucleotides

Question 16.
The character which predominates and clearly seen in F1 Generation is said to be :
(a) Dominant
(b) Recessive
(c) Inherited
(d) None of these
Answer:
(a) Dominant

Question 17.
The Genotypic Ratio of a mono hybrid cross in F2 Generation is :
(a) 3 : 1
(b) 2 : 1
(c) 1 : 2 : 1
(d) 1 : 3
Answer:
(c) 1 : 2 : 1

Question 18.
When two individuals are similar in external appearance but different in their genetic makeup they are called as?
(a) Allele
(b) Dominant
(c) Homozygous
(d) Heterozygous
Answer:
(d) Heterozygous

Question 19.
The phenotypic ratio of a di-hybrid cross in F2 Generation is :
(a) 1 : 4 : 6 : 1
(a) 1 : 2 : 1
(c) 9 : 3 : 3 : 1
(d) 2 : 1 : 4
Answer:
(c) 9 : 3 : 3 : 1

Question 20.
A couple with blood types A and B may have children with blood types
(a) A & B only
(b) AB
(c) A, B, AB & O
(d) A and O
Answer:
(a) A & B only

Question 21.
A gamete contains :
(a) only one allele of a gene
(b) two alleles
(c) three alleles
(c) none of these
Answer:
(a) only one allele of a gene

Question 22.
A character which is expressed in a hybrid is called
(a) Dominant
(b) Recessive
(c) Co-dominant
(d) Epistatic
Answer:
(a) Dominant

Question 23.
How many different kinds of gametes will be produced by a plant having the genotype AABbCC?
(a) Three
(b) Four
(c) Nine
(d) Two
Answer:
(d) Two

Question 24.
If a colour blind woman marries a normal visioned man, their sons will be
(a) Three-fourths colour blind and one-fourth normal
(b) One-half colour blind and one-half normal
(c) All normal visioned
(d) All colour blind
Answer:
(d) All colour blind

Question 25.
The term Genetics first coined by
(a) Mendel
(b) Darwin
(c) Purret
(d) Bateson
Answer:
(d) Bateson

Question 26.
Genes for cytoplasmic male sterility in plants are generally located in:
(a) Nuclear-genome
(b) Mitochondrial genome
(c) Chloroplast genome
(d) Cytosol
Answer:
(b) Mitochondrial genome

Question 27.
A polygenic trait is controlled by 3 genes A, B and C. In a cross A aBbCc × AaBbCc, the phenotypic ratio of the “offsprings was observed as 1 : 6 : x : 20 : x : 6 : 1. What is the possible value of x ?
(a) 3
(b) 9
(c) 15
(d) 25
Answer:
(c) 15

Question 28.
A common test to find the genotype of a hybrid is by:
(a) Crossing of one F₁ progeny with male parent
(b) Crossing of one F₂ progeny with male parent
(c) Crossing of one F₂ progeny with female parent
(d) Studying the sexual behaviour of F₁ progenies
Answer:
(a) Crossing of one F₁ progeny with male parent

Question 29.
A man and a women, who do not show any apparent signs of a certain inherited disease, have seven children (2 daughter and 5 sons). Three of the sons suffer from the given disease but none of the daughters are affected. Which of the following mode of inheritance do you suggest for this disease?
(a) Sex-linked recessive
(b) Autosomal dominant
(c) Sex-limited recessive
(d) Sex-linked dominant
Answer:
(a) Sex-linked recessive

Question 30.
A person with unknown blood group under ABO system, has suffered much blood loss in an accident and needs immediate blood transfusion. His one friend who has a valid certificate of his own blood type, offers for blood donation without delay. What would have been the type of blood group of the donor friend?
(a) Type A
(b) Type B
(c) Type AB
(d) Type O
Answer:
(d) Type O

Question 31.
A self-fertilizing trihybrid plant forms :
(a) 8 different gametes and 32 different zygotes
(b) 8 different gametes and 16 different zygotes
(c) 8 different gametes and 64 different zygotes
(d) 4 different gametes and 16 different zygotes
Answer:
(c) 8 different gametes and 64 different zygotes

Question 32.
Assertion : An organism with lethal mutation may not even develop beyond the zygote stage.
Reason : All types of gene mutations are lethal.
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) Assertion is true statement but reason is false.
(d) Both assertion and reason are false.
Answer:
(c) Assertion is true statement but reason is false.

Question 33.
Excessive growth of hair on the pinna is a feature found only in males because
(a) The gene responsible for the character is recessive in females and dominant only in males
(b) The character is induced in males as males produce testosterone
(c) The female sex hormone estrogen suppresses the character in females
(d) The gene responsible for the character is present on the Y chromosome only
Answer:
(d) The gene responsible for the character is present on the Y chromosome only

Question 34.
Given below is a pedigree chart of a family with five children. It shows the inheritance of attached ear lobes as opposed to the free ones. The squares represent the male individuals and circles the female individuals. Which one of the following conclusions drawn is correct?

(a) The parents are homozygous recessive
(b) The trait is Y-linked
(c) The parents are homozygous dominant
(d) The parents are heterozygous
Answer:
(d) The parents are heterozygous

Question 35.
Grain colour in wheat is determined by three pairs of polygene. Following the cross AABBCC (dark colour) × aabbcc (light colour), in F₂-generation what proportion of the progeny is likely to resemble either parent
(a) One fourth
(b) Less than 5 percent
(c) One third
(d) None of these
Answer:
(b) Less than 5 percent

Question 36.
Haemophilia is more commonly seen in human males than in human females because
(a) This disease is due to a Y-linked recessive mutation
(b) This disease is due to an X-linked recessive mutation
(c) This disease is due to an X-linked dominant
(d) A greater proportion of girls die in infancy
Answer:
(b) This disease is due to an X-linked recessive mutation

Question 37.
Gregor Mendel proposed which of the following concepts?
I. The law of independent assortment
III. The theory of evolution
II. The law of segregation
IV. Natural selection
(a) I, II and IV
(b) I and II
(c) I, II, III and IV
(d) II, III and IV
Answer:
(b) I and II

Question 38.
Hemophilia is a trait carried by the mother and passed to her sons. The allele for hemophilia, therefore,
(a) is carried on one of the ‘mother’s autosomal chromosomes.
(b) can be carried on the X or Y chromosome.
(c) is on the X chromosome and can only be inherited by the son if the mother is a carrier (heterozygous).
(d) is carried in the mitochondrial genome because sons inherit this allele from their mothers.
Answer:
(c) is on the X chromosome and can only be inherited by the son if the mother is a carrier (heterozygous).

Question 39.
Which of the following statements is/are true?
I. A human with two X chromosomes and a Y chromosome is male.
II. A human with one X chromosome is female.
III. All children of a colour blind woman and a man who is not colour blind will carry a colour blind allele.
(a) I and II
(b) II
(c) II and III
(d) I, II and III
Answer:
(a) I and II

Question 40.
True-breeding plants show what phenotype?
(a) They have no mutations
(b) They result from a monohybrid cross
(c) They produce the same offspring when crossed for many generations.
(a) They result from a dihybrid cross.
Answer:
(c) They produce the same offspring when crossed for many generations.

Very Short Answer Type Questions : 1 Mark

Question 1.
Name the plant on which Mendel performed his experiments?
Answer:
Garden Pea (Pisum sativum.)

Question 2.
Define a gene?
Answer:
Gene is a small segment of DNA on a chromosome occupying specific position in which is a hereditary determinant or unit of a biological function.

Question 3.
Write the expanded form of DNA?
Answer:
DNA – Deoxyribonucleic Acid.

Question 4.
Define : Heredity.
Answer:
Heredity is defined as ‘the transmission of characters from parents to the offsprings’.

Question 5.
Give the meaning of variation from biological point of view.
Answer:
From biological point of view, variation means some individual difference(diversity) in the organism of one generation from that of the parental generation.

Question 6.
What is Genetics?
Answer:
Genetics is the branch of biology which studies important aspects of heredity and variation.

Question 7.
What did Mendel propose ?
Answer:
Mendel proposed that for regulation of every character(in an organism) there is a pair of factors.

Question 8.
What happens when a cross is made between two pea plants ?
Answer:
When a cross is made between two pea plants showing different characters, only one character is seen in the offsprings but the successive generations show both characters.

Question 9.
Who showed that gene is a part of chromosome ?
Answer:
T. Boveri and W.S. Sutton showed that gene is a part of chromosome.

Question 10.
Where are genes located ?
Answer:
Genes are located on chromosomes.

Question 11.
Of what is a gene the segment ?
Answer:
A gene is a segment of DNA(deoxyribonucleic acid).

Question 12.
What is meant by homologous chromosomes?
Answer:
Homologous chromosomes are chromosomes occurring in pair and the members of a pair of chromosomes are exactly identical.

Question 13.
What is the difference between prokaryotic and eukaryotic chromosomes ?
Answer:
In prokaryotes only one chromosome occurs whereas in eukaryotes many chromosomes occur in pairs.

Question 14.
What is the difference in number of chromosomes of somatic cells and reproductive cells?
Answer:
The number of chromosomes in reproductive cells is half(haploid) of that in somatic cells(diploid).

Question 15.
When do chromosomes get separated from each other ?
Answer:
Chromosomes get separated from each other during metaphase of cell division.

Question 16.
What do you study in Genetics ?
Answer:
We study important aspects of heredity and variation in Genetics.