Punnett Square practice

Punnett Square Practice

Multiple Choice

In guinea pigs, rough coats (R) are dominant to smooth coats (r). A homozygous rough-coat guinea pig has offspring with a homozygous smooth-coat guinea pig. What percent of the offspring are predicted to have rough coats?

• 0%

• 25%

• 50%

• 100%

Explanation

This question requires you to complete a Punnett square.

It starts off with the first guinea pig, which is a homozygous rough-coat. What does homozygous mean? What would be the genotype?

The second pig is a homozygous smooth-coat guinea pig? What would be the genotype?

Once you figure out the genotypes, the Punnett square is easy.

Multiple Choice

Having freckles is dominant over not having freckles. If two individuals heterozygous for freckles have a child, what is the probability the child will have freckles?

• 0%

• 25%

• 50%

• 75%

Explanation

If it tells you that a trait is dominant, then you should know that it will be represented by a capital letter. In this case, F is dominant and f is recessive.

Then it said it was heterozygous. That means there is both a capital letter and a lowercase letter in the genotype. Both individuals have a genotype of Ff. Ff x Ff will give 2 Ff (freckles), 1 FF (freckles), and 1 ff (no freckles).

Multiple Choice

A tall pea plant (TT) is crossed with a short pea plant (tt). What is the probability that the offspring will be tall?

• 25%

• 50%

• 75%

• 100%

Explanation

This problem already gives you the two parents. All you have to do is set up your Punnett square table and multiply. Remember we don't use the square in biology.

Multiple Choice

Black fur (B) is dominant to white fur (b) in guinea pigs. An F1 cross was conducted and resulted in 100% heterozygous guinea pigs (Bb). What is the genotypic ratio outcome of the F2 generation.

• 1 BB: 2 Bb: 1 bb
• 4 Bb

• 3 Bb: 1 bb

• 2 BB : 1 Bb : 1 bb

Explanation

In this problem, it already tells you that the parents were cross and produced 4 guinea pigs with Bb genotype. For F2, you are asked to "cross" two of those guinea pigs. On one side write Bb for the mother and write Bb for the father. Complete the Punnett square.