Biology [3 marks Question Answer]

	Column I (Term)		Column I (Explanation)
a	genetics	3	Study of laws of inheritance of characters
b	Autosomes	5	Chromosomes other than the pair of sex chromosomes
c	Recessive gene	4	A gene that can express when only in a similar pair
d	Allele	2	The alternative forms of a gene
e	Homologous chromosomes	1	Chromosomes similar in size and shape

F2 generation?

Gametes	R	r
R	RR	Rr
r	Rr	rr

Genotype - 1(Homozygous red) :2 (Heterozygous red):1 (Homozygous white)
Phenotype - 3 (Red) :1(White)

F2 generation

Gametes	T	t
T	TT	Tt
t	Tt	Tt

Genotype - 1(Homozygous tall) :2 (Heterozygous tall):1 (Homozygous dwarf)
Phenotype - 3 (Tall) :1(Dwarf)

Genotype - 1(Homozygous Black Fur) :2 (Heterozygous Black Fur):1 (Homozygous Brown
Fur)
Phenotype - 3 (Black Fur) :1(Brown Fur)

Colour-blindness is caused due to recessive genes which occur on the X chromosome. Males have only one X chromosome. If there is recessive gene present on X chromosome, then the male will suffer from colour-blindness. Females have two X chromosomes. It is highly impossible that both the X chromosomes carry abnormal gene. Hence, if one gene is abnormal and since it is recessive, its expression will be masked by the normal gene present on the other X hromosome. Females are unlikely to suffer from colour-blindness.

Character	Dominant trait	Recessive trait
Flower Colour	Purple	White
Seed Colour	Yellow	Green
Seed Shape	Round	Wrinkled
Pod Shape	Inflated	Constricted
Flower Position	Axial	Terminal

	Monohybrid cross		Dihybrid cross
1	It is a cross between two pure breeding parent organisms with different varieties taking into consideration the alternative trait of only one character.	1	It is a cross between two pure breeding parent organisms with different varieties taking into consideration the alternative trait of two characters.

Mendel's laws of inheritance are :
(i) Law of Dominance : Out of a pair of contrasting characters present together, only one is able to express itself while the other remains suppressed. The one that expresses is the dominant character and the one that is unexpressed is the recessive one.
(ii) Law of Segregation : The two members of a pair of factors separate during the formation of gametes. The gametes combine together by random fusion at the time of zygote formation. This law is also known as 'law of purity of gametes'.
(iii) Law of Independent Assortment : When there are two pairs of contrasting characters, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.

Heterozygous:
The condition in which a pair of homologous chromosomes carries
dissimilar alleles for a particular character.
For example -
(i) A daughter (XXo) from a normal homozygous mother for colour vision (XX) anda colour blind father has one normal and one defective allele (XoY).
(ii) Certain tongue rollers are heterozygous with Rr genotype.