Question

The allele for a widow’s peak has complete dominance over the allele for a straight hairline (w). What is the probability of two parents heterogeneous for a widow’s peak (Ww) having an offspring without a widow’s peak?

25 percent
0 percent
50 percent
75 percent

Answer 1

Option A

Step-by-step explanation:

It is given that widow’s peak trait's allele is completely dominant over straight hairline trait's allele.

This means that in any heterozygous gamete , the characteristics associated with the widow’s peak trait will be expressed thereby subsiding the straight hairline trait

Gamete of the heterogeneous parents (Ww) is W, w

Cross between the two heterogeneous parents will produce following offspring

Ww * Ww

WW, Ww, Ww, ww

Thus out of four offspring, three offspring (WW, Ww, Ww) will have widow’s peak while only one offspring (ww) will have straight hairline

Hence, the probability of an offspring without a widow’s peak is

`(1)/(4) * 100\\= 25`%

Hence, option A is correct

Answer 2

Answer: 25 percent

Step-by-step explanation:

Alleles: W x w

Widows peak x straight hairline

• W shows complete dominance over w; complete dominance involves dominant and recessive alleles
• Dominant alleles always show more influence over recessives

Parents are heterogenous...

∴ their genotypes: Ww x Ww

phenotypes: Widow's peak x Widow's peak

From the punnet square of the parent cross:

F1, offspring: TT; Tt; Tt; tt

genotypes: 1 TT: 2 Tt: 1 tt

∴ the genotypic ratio: 1: 2: 1

phenotypes: Widow's peak; Widow's peak; Widow's peak; Straight

There is one offspring without a widow's peak=
`= (1)/(4)` = 25%