Question

In a test cross, when one parent’s genotype is homozygous dominant,

Answer 1

A. All of the offspring will have the dominant phenotype.

Here is why:

In order to understand this question, you first need to understand some vocabulary.

Homozygous means the same, this means when creating an allele pair, they will both be the same letters. There are two types of homozygous pairs that you will need to look out for. One is homozygous dominant and is represented by both uppercase letters. On the other hand, we have homozygous recessive and is represented by two lowercase letters.

Heterozygous is the opposite, this means different, when creating an allele pair, one letter will be different from the other.

The phenotype and the genotype both describe an allele pair. The phenotype has to do with the appearance, while the genotype has to do with the genetic makeup.

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Homozygous dominant: BB (Dominant in phenotype)

Homozygous recessive: bb (Recessive in phenotype)

Heterozygous: Bb (Dominant in phenotype)

Phenotype: Appearance (Ex: Red flower)

Genotype: Genetic makeup (Ex: BB)

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Now let's look at your question!

If we cross a parent with the genotype that is homozygous dominant (BB), the offspring will all be dominant. Dominant alleles will always overpower recessive ones, and since its asking for the phenotype all of the offspring will be dominant.

Since the question does not state the other parents genotype, we can just pick our own, it will have the phenotype but different genotypes. Below I have picked a heterozygous (Bb).

If it asked for the genotype with the parent being (BB) and let's say the other is (Bb), it would be 2 BB's and 2 Bb's, two homozygous dominants and two heterozygous pairs, which are both dominant.

I have attached a Punnett square below to help you.

Answer 2

3/4 of the offspring will have the dominant phenotype