Brown fur color in mice is dominant to white fur color. What phenotypic ratio would you get if you crossed a white mouse and a heterozygous brown mouse?
Step 1. Write down which allele represents each characteristic: B= brown, b= white
Step 2. Write the genotypes of both parents: the white mouse is bb and the brown mouse is Bb.
Step 3. Write down the cross: bb x Bb
Step 4. List all possible gametes that can be produced by each parent. Do not skip this step!!! A white mouse only produces gametes containing b; the brown mouse produces 50% B gametes and 50% b gametes.
Step 5. Now you are ready to do the PUNNETT SQUARE.
1. A man who is heterozygous for tongue rolling (Tt) marries a woman who is homozygous dominant for tongue rolling (TT). What will be the phenotypes of their offspring?
2. In tomato plants, the gene for purple stems (P) is dominant to its allele for green stems (p). If a homozygous dominant plant is crossed with a homozygous recessive plant, what genotypes and phenotypes would be expected in the offspring?
3. Mary has no freckles and neither does her dad. But Mary's mom has freckles, a dominant trait (F). What is Mary's mom genotype?
4. A man and a woman are both heterozygous for the gene (f) that causes cystic fibrosis, a recessive lung disorder. Do they have the disease? What is the chance that their first child will have cystic fibrosis?
5. In guinea pigs, the allele for short hair is dominant.
a. What genotype would a heterozygous short haired guinea pig have? _______
b. What genotype would a pure-breeding short haired guinea pig have? _______
c. What genotype would a long haired guinea pig have? ________
d. Show the cross for a pure-breeding short haired guinea pig and a long haired guinea pig.