College

Select the correct answer from each drop-down menu.

1. If a heterozygous male with the genotype Ww is mated with a homozygous recessive female of genotype ww, there is a [blank] chance that the offspring will be heterozygous.

[tex]
\[
\begin{tabular}{|c|c|c|}
\hline & W & w \\
\hline w & Ww & ww \\
\hline w & Ww & ww \\
\hline
\end{tabular}
\]
[/tex]

2. If the heterozygous, Ww, is crossed with a homozygous dominant, WW, then the probability of having a homozygous recessive offspring is [blank].

[tex]
\[
\begin{tabular}{|c|c|c|}
\hline & W & w \\
\hline W & WW & Ww \\
\hline W & WW & Ww \\
\hline
\end{tabular}
\]
[/tex]

Answer :

Let's work through each cross step by step.

1. For the cross between a heterozygous male ([tex]$Ww$[/tex]) and a homozygous recessive female ([tex]$ww$[/tex]):

- The male produces two types of gametes: one carrying the [tex]$W$[/tex] allele and one carrying the [tex]$w$[/tex] allele, each with a probability of 0.5.
- The female can only produce gametes carrying the [tex]$w$[/tex] allele.

Therefore, the possible offspring are:

- If the male’s gamete is [tex]$W$[/tex], the offspring’s genotype will be [tex]$Ww$[/tex] (heterozygous).
- If the male’s gamete is [tex]$w$[/tex], the offspring’s genotype will be [tex]$ww$[/tex] (homozygous recessive).

Since half of the male’s gametes carry [tex]$W$[/tex], the probability of obtaining a heterozygous ([tex]$Ww$[/tex]) offspring is

[tex]$$ 0.5 \text{ or } 50\%. $$[/tex]

2. For the cross between a heterozygous individual ([tex]$Ww$[/tex]) and a homozygous dominant individual ([tex]$WW$[/tex]):

- The heterozygous individual produces gametes: one carrying [tex]$W$[/tex] and one carrying [tex]$w$[/tex], each with a probability of 0.5.
- The homozygous dominant individual can only produce gametes carrying the [tex]$W$[/tex] allele.

Therefore, the possible offspring are:

- If the heterozygous partner produces a [tex]$W$[/tex] gamete, the offspring’s genotype will be [tex]$WW$[/tex] (homozygous dominant).
- If the heterozygous partner produces a [tex]$w$[/tex] gamete, the offspring’s genotype will be [tex]$Ww$[/tex] (heterozygous).

Notice that there is no possibility for a [tex]$ww$[/tex] (homozygous recessive) offspring in this cross. Thus, the probability of having a homozygous recessive offspring is

[tex]$$ 0.0 \text{ or } 0\%. $$[/tex]

To summarize:

- The chance that [tex]$50\%$[/tex] of the offspring will be heterozygous in the first cross.
- The probability that there will be any homozygous recessive offspring in the second cross is [tex]$0\%$[/tex].