Question

trait a is dominant to trait a, and trait b is dominant to trait b. if an aabb mother mates with an aabb father, what percent of the offspring will have the aabb genotype?
○ 18.75%
○ 25.0%
○ 12.5%

question 14
2 pts
two genes located near each other on the same chromosomes are said to be:
○ linked
○ at the same locus
○ nearby

Explanation:

First Question (Genotype Probability)

Step1: Analyze Trait A Inheritance

Mother: \( Aa \), Father: \( Aa \). The Punnett square for \( Aa \times Aa \) gives genotypes \( AA, Aa, Aa, aa \). So probability of \( aa \) is \( \frac{1}{4} = 25\% \).

Step2: Analyze Trait B Inheritance

Mother: \( BB \), Father: \( Bb \). The Punnett square for \( BB \times Bb \) gives genotypes \( BB, BB, Bb, Bb \). Probability of \( BB \) is \( \frac{2}{4} = 50\% \).

Step3: Combine Probabilities

Since traits are independent, multiply probabilities: \( 25\% \times 50\% = 12.5\% \)? Wait, no—wait, mother is \( BB \), father is \( Bb \). So mother can only give \( B \), father can give \( B \) or \( b \). So offspring for B: \( BB \) (from \( B \) mother and \( B \) father) or \( Bb \) (from \( B \) mother and \( b \) father). So probability of \( BB \) is \( \frac{1}{2} \) (50%). For A: \( Aa \times Aa \) gives \( aa \) with probability \( \frac{1}{4} \) (25%). Then combined: \( 0.25 \times 0.5 = 0.125 = 12.5\% \)? Wait, no, wait the first options: 18.75, 25, 12.5. Wait, maybe I messed up. Wait mother is \( AaBB \), father is \( AaBb \). Let's do it as two separate crosses.

For gene A: \( Aa \times Aa \). The possible genotypes: \( AA \) (25%), \( Aa \) (50%), \( aa \) (25%). So \( aa \) is 25% (0.25).

For gene B: \( BB \times Bb \). Mother can only give \( B \), father can give \( B \) or \( b \). So offspring: \( BB \) (from \( B \) and \( B \)) or \( Bb \) (from \( B \) and \( b \)). So \( BB \) is 50% (0.5), \( Bb \) is 50% (0.5).

Now, to get \( aaBB \), we need \( aa \) (from A) and \( BB \) (from B). So multiply the probabilities: \( 0.25 \times 0.5 = 0.125 = 12.5\% \)? Wait but wait, maybe I made a mistake. Wait \( Aa \times Aa \): the Punnett square is \( A \) and \( a \) from mother, \( A \) and \( a \) from father. So:

• \( A \times A = AA \)
• \( A \times a = Aa \)
• \( a \times A = Aa \)
• \( a \times a = aa \)

So \( aa \) is 1/4 (25%). Correct.

For \( BB \times Bb \): mother's gametes: \( B \) (only, since she's \( BB \)). Father's gametes: \( B \) or \( b \) (since he's \( Bb \)). So:

• \( B \times B = BB \)
• \( B \times b = Bb \)

So two possibilities, each with 50% chance. So \( BB \) is 50% (1/2).

Thus, probability of \( aaBB \) is \( \frac{1}{4} \times \frac{1}{2} = \frac{1}{8} = 12.5\% \)? Wait but 1/8 is 12.5%, but let's check again. Wait, \( AaBB \) has genotype \( Aa \) for A, \( BB \) for B. \( AaBb \) has \( Aa \) for A, \( Bb \) for B.

So for A: \( Aa \times Aa \) → \( aa \) is 25% (0.25).

For B: \( BB \times Bb \) → \( BB \) is 50% (0.5).

Multiply: 0.25 0.5 = 0.125 = 12.5%. So the answer is 12.5%? Wait but the options are 18.75, 25, 12.5. Wait maybe I messed up the B cross. Wait father is \( Bb \), mother is \( BB \). So mother's gametes: \( B \) (100%), father's gametes: \( B \) (50%) and \( b \) (50%). So when they mate, the possible offspring for B: \( BB \) (B from mother, B from father) and \( Bb \) (B from mother, b from father). So two outcomes, each with 50% chance. So \( BB \) is 50% (0.5). Then A: \( aa \) is 25% (0.25). So 0.25 0.5 = 0.125 = 12.5%. So the answer is 12.5%? Wait but 1/8 is 12.5%, yes. So the correct option is 12.5%? Wait no, wait 0.25 0.5 is 0.125, which is 12.5%. So the answer is 12.5%? Wait but let's check again. Wait \( Aa \times Aa \) gives \( aa \) in 1/4 of cases. \( BB \times Bb \) gives \( BB \) in 1/2 of cases. So 1/4 1/2 = 1/8 = 12.5%. So the answer is 12.5%? Wait but the first option is 18.75, 25, 12.5. So 12.5% is an option. So that's the answer.

Second Question (Gene Linkage)

• "Linked" genes are those located near each other on the same chromosome, which affects their inheritance (they tend to be inherited together).
• "At the same locus" is incorrect because a locus is a specific position on a chromosome, and two genes can’t be at the same locus (they would be alleles).
• "Nearby" is a vague term; the scientific term for genes close on the same chromosome is "linked."

Answer:

First Question: 12.5% (the option with 12.5%)
Second Question: linked (the option "linked")