Answered

For a certain breed of cat, short tails are dominant ([tex]$T$[/tex]) and long tails are recessive ([tex]$t$[/tex]). The Punnett square below shows a cross between two parents. What is the phenotype ratio for this cross?

\begin{tabular}{|c|c|c|}
\hline & [tex]$T$[/tex] & [tex]$t$[/tex] \\
\hline [tex]$t$[/tex] & [tex]$T t$[/tex] & [tex]$t t$[/tex] \\
\hline [tex]$t$[/tex] & [tex]$T t$[/tex] & [tex]$t t$[/tex] \\
\hline
\end{tabular}

A. 1 long, 3 short
B. 3 long, 1 short
C. 4 long, 0 short
D. 2 long, 2 short



Answer :

GinnyAnswer
To determine the phenotype ratio for the given cross, first understand the contributions of each parent.

1. Identify Genotypes of Parents:
- The first parent contributes two alleles: [tex]$t$[/tex] and [tex]$t$[/tex].
- The second parent contributes two alleles: [tex]$T$[/tex] and [tex]$t$[/tex].

2. Set Up the Punnett Square:
- Label the Punnett square with the alleles of each parent:
[tex]\[ \begin{array}{|c|c|c|} \hline & T & t \\ \hline t & Tt & tt \\ \hline t & Tt & tt \\ \hline \end{array} \][/tex]

3. Determine Genotypes in Each Box:
- The top left box results from [tex]$t$[/tex] (from the first parent) and [tex]$T$[/tex] (from the second parent); the genotype is [tex]$Tt$[/tex].
- The top right box results from [tex]$t$[/tex] (from the first parent) and [tex]$t$[/tex] (from the second parent); the genotype is [tex]$tt$[/tex].
- The bottom left box results from [tex]$t$[/tex] (from the first parent) and [tex]$T$[/tex] (from the second parent); the genotype is [tex]$Tt$[/tex].
- The bottom right box results from [tex]$t$[/tex] (from the first parent) and [tex]$t$[/tex] (from the second parent); the genotype is [tex]$tt$[/tex].

4. Summarize the Genotypes:
- We have two [tex]$Tt$[/tex] (short tails) and two [tex]$tt$[/tex] (long tails).

5. Convert Genotypes to Phenotypes:
- [tex]$Tt$[/tex] results in a short tail because the short tail allele ([tex]$T$[/tex]) is dominant.
- [tex]$tt$[/tex] results in a long tail because there are only recessive alleles.

6. Phenotype Ratio:
- We have 2 short tails ([tex]$Tt$[/tex]) and 2 long tails ([tex]$tt$[/tex]).
- Therefore, the phenotype ratio is 2 short tails : 2 long tails.

Consequently, the phenotype ratio for this cross is:

D. 2 long, 2 short

Other Questions