Characters	Expected ratios	Example
Monohybrid cross	Phenotypic = 3 : 1 Genotypic = 1 :2 : 1	Pisum sativum
Dihybrid cross	Phenotypic = 9:3:3:1	Pisum sativum
Incomplete dominance	1 : 2 : 1	Mirabilis jalapa
Complementary genes	9 : 7	Lathyrus odoratus
Supplementary genes	9 : 3 : 4	Coat colour of mice
Collaborative supplementary genes	9 : 3 : 3 : 1	Poultry birds – comb pattern
Dominant epistasis	12 : 3 : 1	Fruit colour in Curcurbita
Recessive epistasis	9 : 3 : 4	Coat colour in mice/pigmentation in onion bulb
Duplicate genes	15 : 1	Fruit shape in Capsella bursapastoris
Polymeric gene	9 : 6 : 1	Cucurbita pepo
Suppresor gene	13:3	Leaf colour of rice

Answer : (c)

Multiple alleles: They are multiple forms of a Mendelian factor or gene which occur on the same gene locus, distributed in different organisms in the gene pool with an organism carrying only two alleles and gametes only one allele. Answer : (a)

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. This goes on to prove that sex has no influence on dominance of trait Answer : (d)

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

Variations are differences found in morphological, physiological, cytological and behavioural traits of individuals belonging to same species. They appear due to (i) Reshuffling of genes/chromosomes by chance of separation of chromosomes (ii) Crossing over (iii) Chance combination of chromosomes during meiosis and fertilization. Answer : (c)

Mendelian principles are the rules of inheritance first discovered by Mendel. There are four principles based on monohybrid cross and polyhybrid cross. The Mendel's four postulates and laws of inheritance are: (1) Principles of Paired Factors (2) Principle of Dominance (3) Law of Segregation or Law of Purity of Gametes (Mendel's First Law of Inheritance) and (4) Law of Independent Assortment (Mendel's Second Law of Inheritance). Answer : (a)

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

All the children will have allele from mother and one from father. For the blood group O the genotype from parents is IO. For the blood group A, the genotype from parents may be IA and IO. For the blood group B, the genotype from parents may be IB and IO. For the blood group AB, the genotype from parents will be IA and IB. From the combination, parent’s blood group genotype will be IAIO and IBIO. Answer : (a)

Answer:(d)

Answer:(a)

Gametes	RY	Ry	rY	ry
RY	RRYY ( Round, yellow)	RRYy (Round, yellow)	RrYY (Round, yellow)	RrYy (Round, yellow)
Ry	RRYy (round, yellow)	RRyy (Round, green)	RrYy (Round, yellow)	Rryy ( Round, green)
rY	RrYY (Round, yellow)	RrYy (Round, yellow)	rrYY (Wrinkled, yellow )	rrYy (Wrinkled, yellow)
ry	RrYy (Round, yellow)	Rryy (Round, green)	rrYy (Wrinkled, yellow)	Rryy (Wrinkled, green)

RRYY (Round, yellow seed) and rryy(wrinkled, green seed) Round, yellow : Round, green : Wrinkled, yellow : Wrinkled, green 9 : 3 : 3 : 1 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)

Characters	Expected ratios	Example
Monohybrid cross	Phenotypic = 3 : 1 Genotypic = 1 :2 : 1	Pisum sativum
Dihybrid cross	Phenotypic = 9:3:3:1	Pisum sativum
Incomplete dominance	1 : 2 : 1	Mirabilis jalapa
Complementary genes	9 : 7	Lathyrus odoratus
Supplementary genes	9 : 3 : 4	Coat colour of mice
Collaborative supplementary genes	9 : 3 : 3 : 1	Poultry birds – comb pattern
Dominant epistasis	12 : 3 : 1	Fruit colour in Curcurbita
Recessive epistasis	9 : 3 : 4	Coat colour in mice/pigmentation in onion bulb
Duplicate genes	15 : 1	Fruit shape in Capsella bursapastoris
Polymeric gene	9 : 6 : 1	Cucurbita pepo
Suppresor gene	13:3	Leaf colour of rice

Answer : (c)

An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Answer : (b)

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 : (b)

In F1 the dominant phenotype appears, the recessive phenotype is not lost but reappears in F2. This suggests that there is no blending of Mendelian factors in F1, but they stay together and only one is expressed. This concept of segregation is often called Mendel’s first principle. While a 3 : 1 ratio in F2 generation of a monohybrid cross suggested that segregation of alleles does take place. Answer : (b)

Gametes	AB	Ab	aB	ab
ab	AaBb	Aabb	aaBb	aabb
ab	AaBb	Aabb	aaBb	aabb

A and B are necessary for normal hearing. For the child to have hearing ability, genotype should be AaBb. This means, gene A and B should be passed from either of the parents. Thus, one parent has genotype of AaBb and one has aabb. AaBb × aabb Answer : (b)

whenever two genes are linked because of their location on a chromosome, their alleles will not segregate independently during gamete formation. As a result, test crosses involving alleles of linked genes will yield phenotypic ratios that stray from the classic Mendelian ratios. Answer : (b)

When neither of the allele is dominant, hybrid produced is intermediate of both the parent. When F1 generation is self-crossed, the phenotypic ratio and genotypic ratio is same. The ratio is 1 : 2 : 1. This phenomenon is called incomplete dominance. Answer : (d)

Meristic variations are changes in the number of recurring parts of an animal, e.g., presence of six digits in man instead of normal five. Substantive variations are changes in the shape, size or colour of an organism. Continuous variation is the variation that has no limit on the value that can occur within a population while discontinuous variation is the variation that has distinct groups for organisms to belong to. Examples of continuous variation include things like a person's height and weight. Examples of discontinuous variation include a person's blood group or the color of a species of bird. Answer : (a)

In sexual reproducing organism, both the parents contribute one set of genome their offspring. Haploid set of chromosomes from each parents result in diploid in offspring. Thus each parent contribute one half of their genes. Answer : (b)

On crossing two similar hybrid ( heterozygous allele), progeny expressing dominant trait and progeny expressing recessive trait is produced. Dominant trait progeny : recessive trait progeny 3 : 1 Recessive progeny = 25% Answer : (c)

Albinism results from inheritance of recessive gene alleles and is known to affect all vertebrates, including humans. It is due to absence or defect of tyrosinase, a copper-containing enzyme involved in the production of melanin. Tyrosinase synthesizes melanin from the amino acid tyrosine. Absence of this enzymes causes albinism. 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

Here, 2 traits are involved. Answer : (d)

Epistasis is the interaction between genes present at two separate loci in which one gene suppresses or masks the expression of other gene. The gene that masks the effect of other gene is known as inhibiting or epistatic factor and the one which is being prevented from exhibiting itself is known as hypostatic factor. Answer : (b)

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

Answer : (c)

Number of combination = 2n where n is pair of chromosome 223= 8.6 million Answer : (a)

Epistasis is the interaction between genes present at two separate loci in which one gene suppresses or masks the expression of other gene. The gene that masks the effect of other gene is known as inhibiting or epistatic factor and the one which is being prevented from exhibiting itself is known as hypostatic factor. Answer : (a)

In formation of gametes, allele separate and one set of allele appear in one gamete. AaBbCDdEe has 5 types of allele i.e., it has 5 traits. No. of gametes = (2)n where n = no of traits (heterozygous allele) Number of gametes = (2)5 = 32 Answer : (d)

Answer : (a)

Law of segregation and Law of independent assortment are based on the mechanism of meiosis, because these principles show segregation of characters and independent movement of characters. Answer : (b)

Child having blood group O has genotype IOIO. Each allele comes from each parent. IO genotype is present in blood group A, B and O. So parents with blood group AB(both parents) , or AB and O Answer : (a)

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 : (c)

Gametes	CP	Cp	cP	cp
CP	CCPP (purple)	CCPp (purple)	CcPP (purple)	CcPp (purple)
Cp	CCPp (purple)	CCpp (white)	CcPp (purple)	Ccpp (white)
cP	CcPP (purple)	CcPp (purple)	ccPP (white)	ccPp (white)
cp	CcPp (purple)	Ccpp (white)	ccPp (white)	Ccpp (white)

Sweet pea (Lathyrus odoratus) is an example of complementary genes. Here, the flower colour is purple if dominant alleles of two genes C and P are present together. The colour is white if the double dominant condition is absent. CcPp × CcPp Purple : white = 9 : 7 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 : (c)

A woman with straight hair marries a man with heterozygous curly hair. The chance of first child to have curly hair is 50%, because gene for straight is dominant and present on X chromosome. So, the correct option is ‘ one in two’. Answer : (d)

Epistasis is the interaction between genes present at two separate loci in which one gene suppresses or masks the expression of other gene. The gene that masks the effect of other gene is known as inhibiting or epistatic factor and the one which is being prevented from exhibiting itself is known as hypostatic factor. Pleiotropy is the ability of gene to have multiple phenotypic effect because it influences a number of characters simultaneously. There is no gene interaction in recessiveness or dominance. Answer : (c)

A man with genotype EEFfGgHH can produce 4 types of sperms and these are EFGH, EFgH, EfGH, EfGH.  A woman with genotype IiLLMmNn can produce 8 types of eggs and these are ILMN, ILMn. ILmN, ILmn, iLMN, iLMn, iLmN. ilmn, Sperm and ova are gametes. Number of gamete = (2)n where n = number of heterozygous gene. Man has genotype EEFfGgHH. It has 2 heterozygous gene Ff and Gg. Sperms = 22 = 4 Female has genotype IiLLMmNn. It has 3 heterozygous gene pair Ii, Mm and Nn. Ova = 23 = 8 Answer : (b)

Skin colour, height and eye colour are example of polygenic inheritance. Answer : (a)

Gametes	TR	Tr	tR	tr
tr	TtRr (tall, red)	Ttrr (tall, white)	ttRr (dwarf, red)	ttrr (dwarf, white)
tr	TtRr (Tall, red)	Ttrr (Tall, white)	ttRr (dwarf, red)	ttrr (dwarf, white)

TtRr × ttrr Tall plants having red flower = 2/8 i.e., 25% Answer : (a)

Round seeded plant : Wrinkled seeded plant are in 1:1 Thus, most suitable option is option (a) Answer : (a)

Traits	Dominant	Recessive
Plant height	Tall (1.2 – 2.0m)(T)	Dwarf (0.25 – 0.5m) (t)
Flower position	Axillary (A)	Terminal (a)
Pod colour	Green (G) or (Y)	Yellow (g) or (y)
Pod shape	Full or inflated (I) or (C)	Constricted (i) or (c)
Flower colour	Violet (V) or (W)	White (v) or (w)
Seed shape	Round (R) or (W)	Wrinkled (r) or (w)
Seed colour	Yellow (Y) or (G)	Green (y) or (g)

Answer : (c)

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

Answer : (d)

Answer : (d)

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 : (d)

Gametes	Y	y
y	Yy (yellow)	yy (yellow)
y	Yy (yellow)	yy (green)

Yy (heterozygous yellow seed) × yy (green seed) Yy (yellow) : yy (green) 1 : 1 50 : 50 Answer : (d)

Multiple alleles: They are multiple forms of a Mendelian factor or gene which occur on the same gene locus, distributed in different organisms in the gene pool with an organism carrying only two alleles and gametes only one allele. Answer : (a)

Gametes	ABC	AbC
ABC	AABBCC	AABbCC
AbC	AABbCC	AAbbCC

AABbCC × AABbCC Phenotypic ratio Dominant trait : recessive trait 3 : 1 Answer : (c)

Multiple alleles control inheritance of blood group. Answer : (d)

Gametes	RT	Rt
rt	RrTt (red fruit, tall)	Rrtt (red fruit, short )
rt	RrTt (red fruit, tall )	Rrtt (red fruit, dwarf)

RRTt ( red fruit, tall ) × rrtt ( white fruit, dwarf ) Tall plant with red fruits = 2/4 = 50% Answer : (d)