Question

\(\mathrm{F}_{1}\) offspring of the cross \(A A \times a a\) are \(\mathrm{F}_{1}\) offspring of the cross \(A A \times a a\) are a. all \(A A\) c. all \(A a\) b. all \(a a\) d. \(1 / 2 A A\) and \(1 / 2\) aa a. all \(A A\) c. all \(A a\) b. all \(a a\) d. \(1 / 2 A A\) and \(1 / 2\) aa

Short answer

All \(F_1\) offspring are \(Aa\).

Step-by-step solution

Determine the Parent Genotypes

Identify the genotypes of the parent organisms involved in this genetic cross. We have one parent with the genotype \(AA\) and the other with the genotype \(aa\).

Predict the Gametes

Determine the gametes produced by each parent. The \( AA \) parent can only produce gametes carrying the \(A\) allele, while the \( aa \) parent can only produce gametes carrying the \(a\) allele.

Perform the Genetic Cross

Create a Punnett square to predict the genotype of the \(F_1\) offspring. Each gamete from the \(AA\) parent combines with each gamete from the \(aa\) parent to create the offspring genotype.

Define the Offspring Genotype

Combine one allele from each parent: \(A\) from the \(AA\) parent and \(a\) from the \(aa\) parent, resulting in all offspring being \(Aa\).

Interpret the Result

Review the possible answers: 'all \(AA\)', 'all \(Aa\)', 'all \(aa\)', '1/2 \(AA\) and 1/2 \(aa\)'. The result of our cross is that all \(F_1\) offspring are \(Aa\). Therefore, the correct answer is 'all \(Aa\)'.

Key concepts

Genotype

A genotype refers to the genetic makeup of an organism, specifically the combination of alleles it inherits from its parents. In the context of our exercise, think of genotypes like a recipe. The way these recipes are written determines an organism’s traits.
For example:

• The genotype "AA" means the organism has two copies of the dominant allele 'A'.
• The genotype "aa" suggests that both alleles are recessive 'a'.
• The genotype "Aa" means the organism has one copy of each allele, one dominant and one recessive.

We use genotypes like a map to understand potential traits, but it's important to remember that environmental factors can also shape how these traits are expressed.

Allele

An allele is a variant form of a gene. Think of it as different flavors of the same ice cream. Some flavors might be more common or 'dominant', while others might be less common or 'recessive'.
In genetic terms:

• Alleles appear in pairs, one from each parent.
• For example, in our exercise, the 'A' allele is dominant over the 'a' allele.

This means if an organism has at least one 'A' allele (like in "Aa", or "AA"), it will showcase the trait associated with 'A'. The recessive 'a' trait only shows when both alleles are 'aa'.

Genetic Cross

A genetic cross involves mating two individuals to analyze the inheritance patterns of specific traits. In our case, we're evaluating how alleles combine to form the genotype of the offspring.
The process of a genetic cross can often be visualized using a Punnett Square, which reveals possible genotypes of the offspring:

• By crossing "AA" with "aa", each parent contributes only one type of allele – ‘A’ from one, and ‘a’ from the other.
• The outcome is uniformly "Aa", indicating all offspring have one dominant and one recessive allele.

Genetic crosses help predict how offspring might look or function based on their genetic makeup.

Gamete

A gamete is a sex cell that carries genetic information from the parent, but only half of the genetic information compared to normal body cells. Think of gametes as little packages that carry half the genetic 'instructions' from each parent.
During reproduction:

• Each parent provides gametes that will combine to form a new organism.
• In our exercise, the "AA" parent produces gametes with the "A" allele, while the "aa" parent produces gametes with the "a" allele.

When these gametes come together, they form the genotype of the offspring. This is how traits are inherited from one generation to the next.