Question

in humans, curly hair is dominant over straight hair. which cross below has the correct probabilities listed? a a woman heterozygous for hair curl, a man heterozygous for hair curl will produce 25% straight hair, 75% curly hair b a woman homozygous recessive for hair curl, a man homozygous recessive for hair curl will produce: 100% curly hair c a woman heterozygous for hair curl, a man homozygous recessive for hair curl will produce: 75% straight hair, 25% curly hair d a woman homozygous dominant for hair curl, a man homozygous recessive for hair curl will produce 50% straight hair & 50% curly hair

Explanation:

Step1: Analyze Option A

Let \(C\) represent the dominant allele (curly hair) and \(c\) represent the recessive allele (straight hair). A woman heterozygous (\(Cc\)) and a man heterozygous (\(Cc\)) cross. Using Punnett square:

$$\begin{array}{|c|c|c|} \hline & C & c \\ \hline C & CC & Cc \\ \hline c & Cc & cc \\ \hline \end{array}$$

Genotype ratios: \(CC:Cc:cc = 1:2:1\). Phenotype: Curly (\(CC + Cc\)) = \(\frac{3}{4}=75\%\), straight (\(cc\))=\(\frac{1}{4} = 25\%\)

Step2: Analyze Option B

A woman homozygous recessive (\(cc\)) and a man homozygous recessive (\(cc\)) cross. All offspring will be \(cc\) (straight hair, not curly).

Step3: Analyze Option C

A woman heterozygous (\(Cc\)) and a man homozygous recessive (\(cc\)) cross. Punnett square:

$$\begin{array}{|c|c|c|} \hline & C & c \\ \hline c & Cc & cc \\ \hline c & Cc & cc \\ \hline \end{array}$$

Phenotype: Curly (\(Cc\))=\(\frac{1}{2}=50\%\), straight (\(cc\))=\(\frac{1}{2}=50\%\)

Step4: Analyze Option D

A woman homozygous dominant (\(CC\)) and a man homozygous recessive (\(cc\)) cross. All offspring will be \(Cc\) (curly hair, not 50 - 50)

Answer:

A. a woman heterozygous for hair curl, a man heterozygous for hair curl will produce 25% straight hair, 75% curly hair