Question

1. In humans, dark hair (D) is dominant over blond hair (d). If a heterozygous dark haired man had a son with his blond haired wife, what would the probability be that the son would have dark hair like his father? 2. a) In tomatoes, red fruit (R) is dominant over yellow fruit. If a homozygous red fruit plant is crossed with a yellow fruit plant, what are the expected genotypic and phenotypic ratios of the F1 generation? b) if two plants from the F1 generation were crossed what would be the resultant genotypic and phenotypic rations for this cross?

Answer 1

Ans 1 --- given that, Dominant trait = dark hair (D)

Recessive trait = blond hair(d)

heterozygous dark haired man = Dd ---> genotype

Blond hair wife = dd -----> genotype

On crossing dark hair man (Dd) with blond hair wife (dd), the probability of getting a son with dark hair like his father I.e.Dd

Only for having the son --- Dd X dd

	D	d
d	Dd	dd
d	Dd	dd

4 sons from Dd and dd parents are produced out of which 2 have Dd or dark hair like their father.

Probability = 2/4 or 1/2.

Or probability% = 2/4 * 100 = 50%

Ans 2 --- Tomato fruit color;

Red = dominant --- R

Yellow = recessive --- r = ® (something as given in question)

Homozygous red = RR is crossed with yellow fruit = rr.

Ans 2. --- a) F1 genotype and phenotye ratio is ;

Crossing RR X rr

	R	R
r	Rr	Rr
r	Rr	Rr

All are red fruit.

Phenotye = Red fruit or 4

Genotype = all same or Rr type or 4.

Both genotype and phenotye are 4.

Ans 2---b ) when the F1 plants obtained are self crossed. Genotype and phenotye ratios obtained are :

Crossing F1 progeny to obtain F2.

Rr X Rr

	R	r
R	RR	Rr
r	Rr	rr

Phenotyes = 3 Red and 1 Yellow.

Phenotye ratio = 3:1

Genotypes = 1 RR, 2 Rr and 1 rr.

Genotype ratio = 1:2:1

Thank you...

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