Question

The only people with Rh negative blood are people who have inherited two recessive alleles for this trait. But some people who are colorblind have inherited only one recessive allele for this trait. Explain why these traits are different in terms of how many recessive alleles are needed to produce the recessive phenotype. Hint: Think about the above problem and sex chromosomes versus autosomes.

Answer 1

The difference is due to the inheritance pattern. Blood type needs two recessive alleles to express Rh-. Color-blindness needs only one.

What are the blood type and Color-blindness inheritance patterns?

⇒ Blood type is coded by a diallelic Rh gene that expresses complete dominance.

The allele Rh+ dominates over the allele Rh-.

Genotyopes and Phenotypes are as follows,

• Individuals Rh+Rh+ express the possitive phenotype

• Individuals Rh+Rh- express the possitive phenotype

• Individuals Rh-Rh- express the negative phenotype.

To express Rh-, a person must inherit two recessive alleles from their parents.

⇒ Color-blindness is an X-linked condition coded by a recessive allele.

As most sex-linked genes, it is transmitted together with the X chromosome.

The phenotype depends on the number of recessive alleles and the sex of the person.

Genotyopes and Phenotypes are as follows,

• X⁺X⁺ women have normal sight.

• X⁻X⁻ women are completely color-blinded

• X⁺X⁻ women are partially color-blinded.

• X⁺Y Men are not color-blinded

• X⁻Y Men are color blinded.

In this case, only one recessive allele is enough to express the affection.

In conclusion, Blood type needs two recessive alleles to express Rh-. Color-blindness needs only one recessive allele.

You can learn more about the inheritance pattern at

brainly.com/question/25303949

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