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


Sagot :

To determine the phenotype ratio for the given cross, we need to first identify the possible genotypes and then determine the corresponding phenotypes.

The Punnett square is structured as follows:

[tex]\[ \begin{array}{|c|c|c|} \hline & T & t \\ \hline T & TT & Tt \\ \hline t & Tt & tt \\ \hline \end{array} \][/tex]

Let's break down the genotypes and their corresponding phenotypes:
- TT: This genotype is homozygous dominant. Cats with this genotype will have short tails.
- Tt: This genotype is heterozygous. Cats with this genotype will also have short tails since short tails are dominant.
- tt: This genotype is homozygous recessive. Cats with this genotype will have long tails since long tails are recessive.

Now, let's count the number of each genotype from the Punnett square:
- TT: There is 1 square with this genotype.
- Tt: There are 2 squares with this genotype.
- tt: There is 1 square with this genotype.

Next, let's count the number of each phenotype:
- Short tail (dominant phenotype):
- 1 (TT) + 2 (Tt) = 3
- Long tail (recessive phenotype):
- 1 (tt) = 1

Therefore, the phenotype ratio for this cross is 3 short tails to 1 long tail.

So, the correct choice is:
D. 3 short, 1 long