Question

A plant produces purple and white flowers. Purple is dominant to white. If we have a homozygous dominant purple flower and a homozygous recessive flower, which of the following choices are correct? O purple; PP O white; Pp O purple; pp O white; PP

Answer 1

• For each gene there are two alternative forms.These alternative forms are called alleles.The alleles can be either dominant or recessice.Dominant allele is an allele whose phenotype is expressed even in presence of other alleles.A recessive allele is an allele that doesn't get expressed in presence of a dominant allele.If two alleles are different ,dominant allele is expressed and recessive allele is masked.Gene can be homozygous or heterozygous.Heterozygous means of the two alleles one is dominant and other is recessive.Homozygous means both the alleles in a gene is of same type.If the two alleles are dominant type ,they are homozygous dominant and if two alleles are recessive type,it is called homozygous recessive.

In the question,the plant produces purple and white flowers in which purple is dominant over white.The alleles of flower can be P and p.In homozygous dominant, the genotype is PP and the genotype of homozygous recessive flower is pp.Since purple is dominant over white ,the correct answer is purple;PP. The genotype of white flower is pp.Pp also express purple colour as P is dominant over p.

• Brown eye is dominant over blue eyes.The alleles can be B and b.B is the dominant allele and b is the recessive allele.The recessive genotype(blue eyes) is expressed only if both the recessive alleles come together i.e. in homozygous condition.Here the genotype of parents are :Bb( heterozygous individual with brown eyes) and BB (Homozygous individual with brown eyes).

Gametes	B	B
B	BB brown eye	BB brown eye
b	Bb brown eye(heterozygous)	Bb brown eye(heterozygous)

Blue eye is only expressed in homozygous recessive (bb) condition.Since none of the offspring have homozygous recessive genotype there is no chance for baby with blue eyes.Therefore the answer is 0%.

• Colour blindness is a sex linked recessive trait.The genes that produce red and green sensitive proteins are present in in the X chromosome.Mutations in this gene produce colour blindness.This Genetic disorder is passed to the offspring through the X chromosome.This disorder is most common in men.Because males have only one X chromosome that is inherited from mother.But females have two X chromosome.The female get infected only if both the X chromosome have mutation.As colour blindness is a recessive trait,the dominant normal gene will mask the effect of recessive colourblind gene.

The alleles of colourblindness can be: X^N - Normal allele

Xⁿ - recessive allele of colour blindness

In the question ,daughter is colourblind.That means she has homozygous recessive alleles of colour blindness.Genotype will be XⁿXⁿ.Since daughter has both alleles recessive ,both father and mother will have this recessive allele.Since male has only one X chromosome ,that X chromosome has the recessive allele.So the genotype of father can be XⁿY (Colour blind man) and mother can be X^NXⁿ ( phenotypically normal but a carrier of recessive allele).

Therefore the answers are:

Yes,the man is the father of the daughter

Genotype of man - XⁿY

Genotype of women - X^NXⁿ

Genotype of daughter - XⁿXⁿ