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How does the allele that causes sickle cell disease both help and harm people?
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For sickle-cell disease assume S is the dominant allele and s the recessive allele Which genotypes are possible for offspring of a carrier (Ss) and a person who lacks the sickle-cell allele (SS)?
SS,Ss
Which person on the pedigree could not pass the allele for sickle cell disease to his her offspring?
V
Can a person who has been successfully treated for sickle cell disease still transmit the disease-causing allele to offspring?
Sickle-cell anemia can only be transmitted if both partners have the disease.
How is sickle-cell disease a representation of codominance?
It's not sickle-cell itself, but rather being a heterozygous carrier of the disease. People with one dominant and one recessive allele for the disease are immune to malaria without the crippling effects of having sickle-cell anemia. I don't think that it can even represent codominance, though.
This pedigree is for a human genetic disease called sickle cell anemia. Assuming that the allele for the disease is recessive how many of the females shown have the disease?
None. =]
Is caused by a mutated allele that produces a defective form of the protein hemoglobin.?
False, Sickle Cell Disease :))
Can give example about overdominance?
Overdominance is when the heterozygote has an advantage over both the recessive and dominant homozygotes. Sickle cell disease is an example of this. When the individual is homozygous for the sickle cell allele, sickle cell disease is shown. When the the individual is homozygous for the wildtype allele, they appear normal. However, when the individual is heterozygous, he or she appears normal and will also be resistent to malaria.
Why heterozygous for sickled cell anemia are resistant to malaria?
Because individuals who inherit the gene from only one parent produce red blood cells which are distorted. This distortion makes the cells unpalatable to malaria parasites, without seriously harming the individual. This tends to protect against malaria and that protection causes selection for this allele. Individuals who get the sickle cell gene from both parents suffer serious distortion of the red blood cells. This protects against malaria, but also reduces the oxygen-carrying capacity of the red cells to a dangerous degree. This causes a disease called sickle-cell anaemia, which causes selection against the gene. In malarial regions a balance is established. When a population with sickle cell alleles moves to an area with effectively no malaria present, the sickle cell alleles are steadily selected against. This shifts the balance steadily towards low levels.
Hemophilia is caused by a mutated allele that produces a defective form of the protein hemoglobin?
False, Sickle Cell Disease :))
This pedigree is for human genetic disease called sickle cell anemia Assuming that the allele for the disease is recessive how many of the female shown have the disease?
NONE.
How does balancing selection affect the sickle cell allele in central Africa?
The sickle cell allele can be maintained in the central African population, above the frequency of gene mutation (balancing selection), because the heterozygous sickle cell individuals have an advantage in lifespan, in this malaria stricken region, over the homozygous alternatives. Homozygous sickle-sickle individuals die early from the sickle cell disease. Homozygous nonsickle-nonsickle die early from malaria. The heterozygous sickle-nonsickle have a higher survival against malaria and therefore the sickle cell allele is balanced selected.
What allele for the sickle cell trait is with the normal allele?
codominant
