Paper Topic:

Genetics Problems

Genetics Problems

Monohybrid crosses with dominance

2 . In human beings , brown eyes are usually dominant over the blue eyes Suppose a brown-eyed woman , whose father had blue eyes , marries a brown-eyed man whose mother was blue-eyed . What proportion of their children would you predict to have blue eyes ? B brown eyes and b blue eyes . Answer

P generation

heterozygous female CH heterozygous male

Bb Bb

Gametes B b B b B b

BB

Brown eyes bB

Brown eyes B

Bb

Brown eyes bb

p Blue eyes

b Conclusion : Phenotypic ratio 3 :1

Three brown eyes and 1 blue eye

F2 3 . In humans , the tendency to develop freckles when exposed to sunlight is dominant over not forming freckles . F freckles and f no freckles . If a freckled woman marries a non-freckled man and they have ten children all freckled , can you be certain that the woman is homozygous ? If the eleventh child is also freckled , will that prove what the mother 's genotype is

Answer

Fact : we cannot be certain that the woman is homozygous for freckled allele F but we can be certain that the man is homozygous for non-freckled allele f . The woman can either be Ff or FF

If the woman is homozygous for FF alleles , then all their children should be heterozygotes i .e . Ff . thus , 100 freckled . See fig below

P generation

Freckled female CH non freckled male

FF ff

Gametes F F f f F F

Ff

freckled Ff

freckled f

Ff

freckled Ff

Freckled...

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