Question

notice the heterozygous (bb) individual has an intermediate phenotype, halfway between the two homozygous individuals. this is called incomplete dominance.

1. explain how incomplete dominance differs from a dominant-recessive pair of alleles. (hint: think about the phenotypes of heterozygous individuals.)
2. explain how incomplete dominance differs from co - dominance.
3. the parents, michael and danielle, both have light brown skin and bb genotype. draw a punnett square to show how they could have two babies with different color skin – one dark brown and the other tan.

Explanation:

Question 10

Step1: Recall Dominant-Recessive

In dominant - recessive, heterozygotes ($Aa$) show the dominant phenotype (same as $AA$), recessive ($aa$) is different.

Step2: Recall Incomplete Dominance

In incomplete dominance, heterozygotes ($Bb$) have a phenotype intermediate between the two homozygotes (e.g., $BB$ is one, $bb$ is another, $Bb$ is in - between).

Step1: Define Incomplete Dominance

In incomplete dominance, the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes (e.g., red ($RR$) + white ($rr$) = pink ($Rr$)).

Step2: Define Co - dominance

In co - dominance, both alleles in a heterozygote are fully expressed, and the phenotype shows both traits (e.g., blood type AB has both A and B antigens).

Step3: Compare the Two

In incomplete dominance, there is a blending of traits. In co - dominance, both traits are expressed simultaneously without blending.

Step1: Determine Parental Genotypes

Both parents have genotype $Bb$ (light brown skin, incomplete dominance: assume $BB$ is dark brown, $bb$ is tan, $Bb$ is light brown).

Step2: Set Up Punnett Square

	B	b
b	Bb	bb

Step3: Analyze Offspring Genotypes/Phenotypes

• $BB$: dark brown (1/4 chance)
• $Bb$: light brown (2/4 chance)
• $bb$: tan (1/4 chance)

So, there is a 1/4 chance for $BB$ (dark brown) and 1/4 chance for $bb$ (tan), so it is possible to have one baby with $BB$ (dark brown) and one with $bb$ (tan).

Answer:

In dominant - recessive, heterozygous individuals show the dominant phenotype (same as homozygous dominant). In incomplete dominance, heterozygous individuals have a phenotype intermediate between the two homozygous phenotypes (not matching either homozygous phenotype exactly).

Question 11