Question

In: Biology

a. What is heterozygote advantage? b. How does heterozygote advantage lead to maintenance of genetic variation?


a. What is heterozygote advantage?  

b. How does heterozygote advantage lead to maintenance of genetic variation?

Solutions

Expert Solution

2a.

A. heterozygote advantage:-


In a small number of cases, humans do show a heterozygote advantage, in which the fitness of the heterozygote is superior to either homozygote. The best known example is the β-hemoglobin locus and its relationship to sickle cell disease. Adult hemoglobin is composed of four polypeptides: two α chains and two β chains, coded for by different genes. The β chain is a sequence of 146 amino acids, with glutamic acid in position 6. This normal hemoglobin is referred to as type A. In sickle cell disease, a mutation causes glutamic acid to be replaced by valine at position 6 and is referred to as hemoglobin S. Individuals who are homozygous for the S allele (SS) have sickle cell disease. Untreated, this condition is lethal, and affected individuals do not survive to be old enough to have offspring.
If there were no selective advantage to the recessive allele, we would expect it to slowly be removed from the gene pool, and the frequency of individuals with sickle cell disease should approximate the mutation rate of the normal A allele to the S allele, which is extremely rare. The disease, however, is relatively common in western and central Africa, where the frequency of S allele can be over 15 percent. The reason for this high frequency is due to the heterozygote AS being resistant to the malarial parasitePlasmodium falciparum.Thus in areas where malaria is common, AS individuals, who possess one sickling allele, have an advantage over AA individuals, who possess none. Copies of the S allele are lost from the gene pool when they occur in individuals affected with sickle cell disease since they do not reproduce, but more copiesare created in the offspring of AS individualssince they are resistant to a severe parasitic disease, namely malaria. This advantage compensates for the loss of individuals with sickle cell disease, and therefore keeps the S gene at a relatively high frequency in western and central African populations. Other hemoglobin abnormalities, including hemoglobin C and E, also seem to have the same effect as sickle cell disease, though the effect is not as pronounced.Thalassemia is another hemoglobin disorder that causes severe anemia. There are two types, α and β, which are due to mutations at the α and β hemoglobin loci respectively. The disease has its highest frequency in areas bordered by the Mediterranean Sea, especially Sardinia, Greece, Cyprus, and Israel. Similar to sickle cell disease, the disorder is fatal at an early age and the heterozygotes are resistant to malaria


2.b

The impact ofheterozygote advantageto genetic variation in a population:-

because heterozygotes carry two different alleles, they increase the chances of those alleles appearing in thepopulation and maintaining variation.homozygotes only pass the same allele, asort of redundancy, if you will, in the population.


Related Solutions

30. What is the source of genetic variation? How does meiosis contribute to the maintenance of...
30. What is the source of genetic variation? How does meiosis contribute to the maintenance of genetic diversity? 31. Describe the preconditions for natural selection to operate and what the results of the natural selection will be. 32. Use the HW equations to solve simple population genetics problems with and without selection. 33. Hardy-Weinberg equilibrium tells us the conditions under which populations will not evolve. So what types of things may lead to a population evolving? How do these things...
What does recombining genetic variation mean. How does it happen?
What does recombining genetic variation mean. How does it happen?
a. Explain how genetic drift can lead to a reduction in the genetic variation within a population.
a. Explain how genetic drift can lead to a reduction in the genetic variation within a population. b. Under what conditions is drift most likely to occur?
variation - What is the main genetic source of variation? Why role does variation play in...
variation - What is the main genetic source of variation? Why role does variation play in evolution? Why is variation important for the survival of a species?
What is meant by genetic variation and what are factors that contribute to genetic variation? What...
What is meant by genetic variation and what are factors that contribute to genetic variation? What is the difference between benign tumor and malignant tumor? What are the stages (know correct sequence) of mitosis? What is the sex chromosome combination that determines male and female gender? What does the cell theory say?
Which processes lead to most genetic variation in sexually reproducing organisms?
  Which processes lead to most genetic variation in sexually reproducing organisms?   Select all that apply.   random fertilization   cytokinesis   crossing over   independent assortment of chromosomes in meiosis
Genetic variation is essential for plant breeding. What are the main causes of genetic natural variation...
Genetic variation is essential for plant breeding. What are the main causes of genetic natural variation in plants? Describe at least three possible mechanisms for genetic natural variation to arise naturally, and how they occur.
1. Identify and describe how meiosis helps contribute and lead to genetic variation in sexually reproducing organisms
1. Identify and describe how meiosis helps contribute and lead to genetic variation in sexually reproducing organisms2. Describe how meiosis accomplishes a reduction in chromosome number 3. Contrast the major differences between the daughter cells in meiosis and the daughter cells in mitosis [ fill in the chart below] 
1. How does first-mover advantage lead into a sustainable competitive advantage? 2. Where does the Austrian...
1. How does first-mover advantage lead into a sustainable competitive advantage? 2. Where does the Austrian Trade Cycle Theory fit into first-mover advantage? 3. How does efficiency impact collusion?
1. How does first-mover advantage lead into a sustainable competitive advantage? 2. Where does the Austrian...
1. How does first-mover advantage lead into a sustainable competitive advantage? 2. Where does the Austrian Trade Cycle Theory fit into first-mover advantage? 3. How does efficiency impact collusion?
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT