Different combinations of gametes are theoretically represented in a square tabular form known as ‘Punnett Square’. Reference NCERT 12th Biology text book, Page 93, summary Answer : (d)

Gamate	HbA	HbS
HbA	HbA HbA Normal	HbA HbS Carrier
HbS	HbA HbS Carrier	HbS HbS diseased

Sickle cell anaemia is an autosome linked recessive trait. Homozygous HbS HbS shows diseased phenotype. Hetrozygous HbA HbS are carrier. Female and male both are heterozygous i.e. carrier of disease. Female HbA HbS × Male HbA HbS Progeny that will be diseased = ¼ = 25% Answer : (d)

Experimental verification of the chromosomal theory of inheritance by Thomas Hunt Morgan and his colleagues, led to discovering the basis for the variation that sexual reproduction produced. Morgan worked with the tiny fruit flies, Drosophila melanogaster Answer : (d)

Genes for flower colour in snapdragon shows incomplete dominance which is an exception of Mendel's first principle i.e. Law of dominance. Whereas Law of segregation is universally applicable. When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly. This is known as the law of segregation. Answer : (d)

Klinefelter syndrome (47,XXY) results from an additional X chromosome on an XY background; therefore, this condition affects only males. The vast majority of men with Klinefelter syndrome are infertile and can't father a child the usual way. Answer : (b)

Answer : (c)

Sickle-cell anaemia : This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). Sickle cell disease is caused by a mutation in the hemoglobin-Beta gene found on chromosome 11. Thalassemia : This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous).. Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait. Haemophilia : This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. Answer : (a)

Answer : (a)

Crossing of F1 individual having dominant phenotype with its homozygous recessive parents is called test cross. The test cross is used to determine whether the individuals exhibiting dominant characters are homozygous or heterozygous. Answer : (c)

Blood type (phenotype)	Genotype	Antigen	Antibodies
A	IAIA or IAIO	A	b
B	IBIB or IBI0	B	a
AB	IAIB	Both A and B	Neither a nor b
O	IOIO	Neither A nor B	Both a and b

The four basic ABO phenotypes are O, A, B, and AB. Answer : (b)

Answer : (c)

Word genetics comes from the word gene. The term was coined and used for the first time by W. Bateson(1905). Answer : (a)

Since pea plant is homozygous, it will produces only one type of gamete i.e., tr. Answer : (c)

Gametes of F2	BS	Bs	bS	bs
BS	BBSS	BBSs	BbSS	BbSs
Bs	BBSs	BBss	BbSs	Bbss
bS	BbSS	BbSs	bbSS	bbSs
bs	BbSs	Bbss	bbSs	bbss

BBSS : BbSS : BBSs : BbSs 1 : 2 : 2: 4 Answer : (d)

The ability of a gene to have multiple phenotypic effect because it influences a number of characters simultaneously is known as pleiotropy. The gene having a multiple phenotypic effect because of its ability to control expression of a number of characters is called pleiotropic gene Answer : (b)

Baby has blood group A. It means the genotype is either IAIA or IAIO. One of the allele comes from mother and another from father. So both the parents should have any of the following blood group. 1) Both the parents have blood group A. 2) Husband O, wife AB vice-versa 3) Husband A, wife B or vice-versa 4) Husband AB, wife A or vice-versa. Answer : (c)

Round yellow : Round green : Wrinkled yellow : Wrinkled green 9 : 3 : 3 : 1 Round green = 3/16 Answer : (d)

Pure line varieties are raised by selection of individual plants from a traditional variety or some other mixed population and thus, they are homozygous, i.e., true breeding and homogeneous as they are genetically similar. A pure line produces a single type of gametes and parental combinations in the progeny. Pure line breed refers to a group of identical individuals that always produce offspring of the same phenotype when intercrossed. This occurs only when they are homozygous. Thus, the correct answer is option a. Answer : (a)

No. of traits (n)	Experiment	Types of gametes (2n)	No. of offsprings (gametes)2	No. of phenotype (2n)	No. of genotype (3n)	Phenotypic ratio	Genotypic ratio
1	Monohybrid cross	2	4	2	3	3:1	1:2:1
2	Dihybrid cross	4	16	4	9	9:3:3:1	2:4:2:1:2:1:1:2:1
3	Trihybrid cross	8	64	8	27	(3:1)3	(1:2:1)3

Answer : (a)

A true breeding is a kind of breeding wherein the parents would produce offspring that would carry the same phenotype. This means that the parents are homozygous for every trait. Since only one trait i.e yellow colour is expressed in F1 generation, it means yellow colour seed is a dominant allele. Answer : (b)

Gametes	WY	Wy	wY	wy
wY	WwYY (white)	WwYy (white)	wwYY (yellow)	wwYy (yellow)
wy	WwYy (white)	Wwyy (white)	wwYy (yellow)	wwyy (green)

Fruit colour of Cucurbita is governed by gene which produces yellow colour in dominant state (Y) and green colour in recessive state (yy). There is non-pigment forming epistatic gene which in dominant state (W) produces white colour while in recessive state it allows the yellow and green colour expression. WwYy (white fruit) × wwYy (yellow fruit ) White : yellow : green = 4 : 3 : 1 Answer : (c)

	IA	IO
IA	IAIA (A blood group)	IAIO (A blood group)
IB	IAIB (AB blood group)	IBIO (B blood group)

Parent having blood group A has genotype IAIA or IAIO. Parent having blood group AB has genotype IAIB. Answer : (b)

Crossing of F1 individual having dominant phenotype with its homozygous recessive parents is called test cross. The test cross is used to determine whether the individuals exhibiting dominant characters are homozygous or heterozygous. Answer : (a)

During Anaphase of meiosis I, the two chromosome pairs can align at the metaphase plate independently of each other. Answer : (a)

term recombination means the generation of non-parental gene combinations. Morgan and his group also found that even when genes were grouped on the same chromosome, some genes were very tightly linked and showed very low recombination, while others were loosely linked and showed higher recombination. Answer : (c)

The cross in which only alternate forms of a single character are taken into consideration is called monohybrid cross. Answer : (c)

Mendel was lucky in choosing characters which showed complete independent assortment. He only took those traits for his studies which did not show linkage, interaction or incomplete dominance. Answer : (c)

Recessive allele is factor of an allele pair which is unable to express its effect in the presence of its contrasting factor in heterozygote. Example t in Tt. Answer : (d)

Tall : Dwarf 3 : 1 Answer : (b)

A pair of contrasting characters is called allelomorph or allele. The term allele was given by W.Bateson for alternative forms of same gene. Answer : (a)

In homozygous condition, organisms have two similar genes or alleles for a particular character in a homologous pair of chromosomes. Answer : (a)

All the progeny of F1 generation has genotype Aa. A is dominant and a is recessive, thus F1 generation has external characters i.e., phenotype of dominant allele. Phenotype of F1 generation is A. Answer : (c)

Environmental variations are those variations which are merely due to environment. These variations are temporary and have nothing to do with the next generation. Continuous variation refers to the type of genetic variation, which shows an unbroken range of phenotypes of a particular character in the population while discontinuous variation refers to the type of genetic variation, which shows to or more separate forms of a character in the population. Answer : (b)

A pair of contrasting trait is called allele. From the given data, one can identify that there two pair of allele A and A, B and b. Answer : (a)

No. of traits (n)	Experiment	Types of gametes (2n)	No. of offsprings (gametes)2	No. of phenotype (2n)	No. of genotype (3n)	Phenotypic ratio	Genotypic ratio
3	Trihybrid cross	8	64	8	27	(3:1)3	(1:2:1)3

Answer : (c)

Mendel conducted experiments on garden peas (Pisum sativum) and formulated the laws which explain the manner of inheritance of characters. Answer : (c)

No. of traits (n)	Experiment	Types of gametes (2n)	No. of offsprings (gametes)2	No. of phenotype (2n)	No. of genotype (3n)	Phenotypic ratio	Genotypic ratio
1	Monohybrid cross	2	4	2	3	3:1	1:2:1
2	Dihybrid cross	4	16	4	9	9:3:3:1	2:4:2:1:2:1:1:2:1
3	Trihybrid cross	8	64	8	27	(3:1)3	(1:2:1)3

individuals of genotype 'YyRrTt, means that no. of traits is 3. it's a formula just get it.... genotype=3n; phenotypes=2n for YyRrTt....so just count n=3 thus 33 = 27 gnotypes and 23 = 8 phenotypes ... now if it is YYRrTt then n=2 Answer : (d)

Tall : Dwarf = 45 : 14 that is approximately 3 : 1. This happens when both the parents are identical and allele is heterozygous. Parents are Tt and Tt Answer : (c)

The Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach in 1905. The diagram is used by biologists to determine the probability of an offspring having a particular genotype. Answer : (b)

Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits. Such a gene that exhibits multiple phenotypic expression is called a pleiotropic gene. Polygenic inheritance occurs when one characteristic is controlled by two or more genes Answer : (d)

Gametes	TG	Tg	tG	tg
TG	TTGG (tall,green)	TTGg (tall, green)	TtGG (tall,green)	TtGg (tall, green)
Tg	TTGg (tall, green)	TTgg (tall, yellow)	TtGg (tall, green)	Ttgg (tall, yellow)
tG	TtGG (tall, green)	TtGg (tall, green)	ttGG (dwarf, green)	ttGG (dwarf, green)
tg	TtGg (tall, green)	Ttgg (tall, yellow)	ttGG (dwarf, green)	ttGG (dwarf, green)

F2 generation Dwarf F2 plants = 4 Answer : (c)

Mendel studied traits which were on different pairs of homologous chromosomes. That is why he concluded that gene pairs segregate independently of one another. Mendel’s gene pairs did not show linkage. Answer : (a)

Reciprocal cross: A set of two reciprocal crosses means that the same two parents are used in two experiments in such a way that if in one experiment, ‘A’ is used as female parent and ‘B’ is used as male parents, in other experiments ‘A’ will be used as male parents and ‘B’ will be used as female parents. Thus the reciprocal crosses involve two crosses concerning the same characteristic, but with reverse sexes. Answer : (d)

In genetics, dominance is the phenomenon of one variant of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome.. Dominant allele is one of the factor of an allele pair which can express itself whether present in homozygous or heterozygous state. Answer : (c)

	IB	IO
IO	IBIO (B blood group)	IOIO (O blood group)
IO	IBIO (B blood group)	IOIO (O blood group)

Man having blood group A has genotype IBIBI or IBIO. Mother having blood group O has genotype IOIO. Answer : (a)

	IA	IO
IA	IAIA (A blood group)	IAIO (A blood group)
IB	IAIB (AB blood group)	IBIO (B blood group)

Mother may have genotype IAIA or IAIO. Son may have genotype IBIO or IBIB. It means Genotype IB is from father. This implies father may B or AB. Most correct option is option A. Answer : (a)

(i) Characters are controlled by discrete units called factors. (ii) Factors occur in pairs. (iii) In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive). The law of dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the F1 and the expression of both in the F2 . It also explains the proportion of 3:1 obtained at the F2 . Answer : (a)

	IA	IO
IB	IAIB (AB blood group)	IBIO (B blood group)
IO	IAIO (A blood group)	IOIO (O blood group)

Parent having blood group A has genotype IAIA or IAIO. Parent having blood group BB has genotype IBIO. Parents have genotype as IAIO and IBIO. Answer : (b)

Gametes	AB	Ab
aB	AaBB	AaBb
ab	AaBb	Aabb

Marriage between related individuals are risky. It is because the recessive alleles in the gene pool will accumulate. If the recessive allele, which reaches the female individual is heterozygous, female is called as carrier. Then the gene gets transferred to further generations, and in male child the defective gene will be expresses to cause disease AABb × aaBb → AaBB : AaBb : Aabb : aabb = 1 : 2 : 1 : 0 Answer : (a)

No. of traits (n)	Experiment	Types of gametes (2n)	No. of offsprings (gametes)2	No. of phenotype (2n)	No. of genotype (3n)	Phenotypic ratio	Genotypic ratio
2	Dihybrid cross	4	16	4	9	9:3:3:1	2:4:2:1:2:1:1:2:1

Answer : (a)