Question

In humans, almond shaped eyes are dominant to round shaped eyes and long eyelashes are dominant to short. A man who has round eyes and homozygous long eyelashes marries a woman who is heterozygous for both traits. Determine the phenotypic ratio. If they have 8 children, how many will have almond shaped eyes with long eyelashes?

Answer 1

The phenotypic ratio of children with almond-shaped eyes and long eyelashes to those with round eyes and long eyelashes is 1:1, or 50% for each phenotype. On average, 4 out of 8 children will have almond-shaped eyes with long eyelashes.

Step-by-step explanation:

We need to determine the phenotypic ratio of the offspring of the cross between a man with round eyes and homozygous long eyelashes and a woman who is heterozygous for both almond-shaped eyes and long eyelashes. To solve this, we'll use a Punnett square.

Let A represent the allele for almond-shaped eyes, and A represent the allele for round eyes. For eyelash length, we'll use L for long eyelashes and l for short eyelashes. The man's genotype for eyes is aa (since he has round eyes) and LL for eyelashes (homozygous long). The woman's genotype is Aa for eyes and Ll for eyelashes.

The Punnett square for eye shape would show that 50% of their children would have genotype Aa (almond-shaped eyes) and 50% aa (round eyes). For eyelash length, 100% of their children will have long eyelashes since the man has the homozygous dominant trait (LL).

Since there are two independent traits, we can use the product law of probability to find the phenotypic ratio. The ratio of having almond-shaped eyes with long eyelashes is 50%, and round eyes with long eyelashes are also 50%. If the couple has 8 children, on average, 4 will have almond-shaped eyes with long eyelashes.

Answer 2

The phenotypic ratio is almond shaped long lashes : round shaped long lashes : round shaped short lashes =2:1:1.

4 children will have long eyelashes and almond shaped eye.

Step-by-step explanation:

Let the gene for eye shape be E and gene for eyelashes be L.

E denotes the almond shaped eye which is dominant over e which is round eye.

L denotes long eyelashes which is dominant over l which is short eyelash.

So genotype of man = eeLL

Genotype of woman = EeLl.

So gametes from man = eL.

Gametes from woman = EL, eL, El and el.

So the genotypic ratio of their children =

EeLL : EeLl: eeLl:eell = 1:1:1:1.

So, assuming these genes maintain the rule of complete dominance, the phenotypic ratio is almond shaped long lashes : round shaped long lashes : round shaped short lashes =2:1:1.

So among 8 children, children with almond shaped eye and long eyelashes will be 4.