On the Indonesian island of Bali, about 3 / 4 of the feral...

On the Indonesian island of Bali, about $3 / 4$ of the feral (stray) cats have a stumpy tail, while only $1 / 4$ of the cats have a long tail. Experiments in which a bunch of random stumpy-tailed cats were mated with each other yielded some stumpy-tailed kittens and some long-tailed kittens. The same experiments with long-tailed cats produced only long-tailed kittens. What do these results show about the genotype of the long-tailed cats? (Hint: Draw Punnett squares using the letter "t" for the tail trait to help you determine which allele is dominant and which is recessive.) (a) They must all be $t$ t. (b) They are both $T t$ and $t t$. (c) They are both $T t$ and $T T$. (d) They must all be $T t$.

On the Indonesian island of Bali, about $3 / 4$ of the feral (stray) cats have a stumpy tail, while only $1 / 4$ of the cats have a long tail. Experiments in which a bunch of random stumpy-tailed cats were mated with each other yielded some stumpy-tailed kittens and some long-tailed kittens. The same experiments with long-tailed cats produced only long-tailed kittens. What do these results show about the genotype of the long-tailed cats? (Hint: Draw Punnett squares using the letter "t" for the tail trait to help you determine which allele is dominant and which is recessive.)
(a) They must all be $t$ t.
(b) They are both $T t$ and $t t$.
(c) They are both $T t$ and $T T$.
(d) They must all be $T t$.

Key Concepts

Test Cross

A test cross involves breeding an organism with an unknown genotype with one that is homozygous recessive for the trait. The resulting offspring's traits help determine the genotype of the unknown parent. This approach is valuable for identifying whether a dominant phenotype is homozygous or heterozygous.

Genotype vs. Phenotype

The genotype refers to the genetic makeup of an organism—the specific alleles it carries—while the phenotype is the observable physical or behavioral expression of those genes. Understanding the relationship between genotype and phenotype is key to interpreting how dominant and recessive alleles manifest as traits.

Mendelian Inheritance

This concept refers to the fundamental principles of how traits are transmitted from parents to offspring through discrete units called alleles. It emphasizes that alleles segregate during gamete formation and recombine during fertilization, leading to predictable patterns in trait distribution among offspring.

Dominance and Recessiveness

In many genetic traits, one allele can mask the effect of another. The dominant allele expresses its trait even when paired with a different allele, while the recessive allele only shows its effect when an individual is homozygous for it. This concept helps explain why certain traits only appear when specific genotypes are present.

Punnett Square Analysis

A Punnett square is a grid tool used to predict the genotypic and phenotypic outcomes of a genetic cross. By representing the alleles from each parent along the rows and columns, it visually demonstrates how alleles combine in the offspring, making it easier to deduce probabilities of different trait expressions.

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