Dihybrid cross

The study of cross involving the inheritance pattern of two characters each of which is

determined by two alleles of a gene for instance, pea plant with  seed colour and seed shape are used in garden pea plant , round seed (RR) is dominant  over wrinkled seed (rr)  , yellow seed (Y)  is dominant over the green seed (y).

When a pure stock of plants having round yellow seeds is crossed with a pure stock  of wrinkled and  seeds, the F1 general offspring all round and yellow.

When a pure stock of plants having round yellow seeds is crossed with a pure stock  of wrinkled and  seeds     , the F1 general offspring all round and yellow.

Parents  ____  Round and yellow  X wrinkled and green

RYRY         x       ryry

Gametes     RY                                      ry

F1                                               RYry   (All round and yellow)

F2 is arranged in prunnet table as follow

RY, ry ,   X  RYry

Gametes :  RY, RY, ry , ry  X   RY  , RY, RY, ry

	RY	RY	ry	ry
RY	RYRY	RYRY	RYrY	RYrg
Ry	RyRy	RyrY	RyrY	Ryry
Ry	RYrY	RyrY	RyrY	rYry
Ry	RYry	Ryry	rYry	ryry

Analysis of phenotype ratio

Round and yellow	9
Round and green	3
Wrinkled and yellow	3
Wrinkled and green	1

Analysis of genotyptic ratio

Homozygons romo yellow	1
Homozygons romo green	1
Homozygons wrinkled yellow	1
Homozygons wrinkled green	1
Homozygons Romo, heterozygons yellow	2
Homozygons romo yellow, Homozygons green	2
Homozygons wrinkled, Homozygons yellow	2
Homozygons romo and yellow	4

Questions

(1)    A man with heterozygous  genotype for blood group B marries a woman with heterozygous

1. what percentage of their children be universal donor?

2.The alternative form of a gene that represents constrasting character is  a/an (A)allele (B)diploid (C)haploid (D)homologue

(3)  If two parents are sickle cell carrier their genotype  would be (A)      Hb ^A  Hb^A  and  Hb^s Hb^s  (b)  Hb^sHb^s and  Hb^s Hb^s  (c)  Hb^A Hb^s and  Hb ^A Hb^s  (D)  Hba Hb^A  and  Hb^A Hb^A