9.11-9.15: Variations on Mendel's Laws Flashcards
(31 cards)
Do all sexually reproducing beings follow Mendel’s Laws?
No, not exactly.
In Mendel’s pea experiment, plants with a dominant gene became completely purple. This is an example of_____
complete dominance.
What is incomplete dominance?
When a trait caused by the dominant gene is not at its “full strength” because it is heterozygote.
Give an example of incomplete dominance?
Snapdragon flowers, which have red and white variations, can make a pink flower in a dominant heterozygote combination. This is because less red pigment is produced in a heterozygote.
Give an example of incomplete dominance in humans.
Hypercholesterolemia: a disease where cells designed to have protein receptors for LDL (low-density lipoproteins aka cholesterol) do not and it causes a buildup if cholesterol in the blood. Normal humans have an HH allele, which gives them enough receptors. People with Hh have half, and those with hh have none.
Do most genes involve two alleles?
No. “Multiple alleles” are more popular.
How many alleles are involved in the ABO blood group phenotype in humans? What are the alleles called? What phenotypes do they produce?
3; they are called I^A, I^B, and i; produce four possible phenotypical blood types: A, B, AB, and O.
In the ABO blood group, what do the letters refer to?
If or if not there is a carbohydrate coated on their blood cells, and if so, which type it is.
Describe the blood types by using their corresponding carbohydrates, antibodies, and genotype.
Type A blood; cells have carbohydrate A; antibodies are anti-B; genotypes are I^A I^A and I^A I. Type B blood; cells have carbohydrate B; antibodies are anti-A; genotypes are I^B I^B or I^B i. Type AB blood; cells have both carbohydrates; have no antibodies in blood; genotype is I^A I^B. Type O blood; has no carbohydrates; both anti-A and anti-B antibodies; genotype ii.
Where do the positive and negative signs on blood type come from?
A completely different gene.
Why is matching the blood types of blood transfusions so important?
If a person’s blood system were to receive a blood type with certain carbohydrates foreign to them, the antibodies would attack the blood cells. If this happens, the blood could clump together and kill the recipient.
Why are people with AB blood known as the universal recipient?
Because they have no antibodies to attack foreign blood cells.
Why are people with O blood type known as the universal donor?
Because, without any foreign carbohydrates, type O blood can successfully enter a foreign system without upsetting antibodies.
What does I^X do, in the ABO blood group?
Adds a covering of carbohydrate “X” to blood cells. Note that the allele “i” adds nothing.
How do patterns of dominance work within the ABO blood group? How is this different from Mendelian Genetics?
I^A and I^B are dominant to i. However, neither I^A or I^B is dominant to each other, making themselves codominant.
What is the key difference between codominance and incomplete dominance?
Incomplete dominance is a blending of traits, codominance includes both distinct traits.
End of 9.12 Question: Maria has type O blood, and her sister has type AB blood. The girls know that both of their maternal grandparents are type A. What are the genotypes of the girls’ parents?
Their mother is type I^A i and their father is I^B i.
Define pleiotropy
one gene influencing many characters. (as opposed to one character)
Describe sickle-cell disease
Red blood cells produce abnormal hemoglobin proteins, which link together and crystallize especially when there is low oxygen content in the blood. The hemoglobin looks like a “sickle” crescent shaped with jagged edges, when crystallized. These cells are destroyed easily, causing anemia and weakening of the body. Causes blood clots, which can lead to kidney and heart failure, and spleen and brain damage. There is no cure, but blood transfusions can help.
What do the alleles of the gene need to look like in order for sickle cell disease to happen?
The allele that causes sickle-cell disease is considered recessive. So, it needs to be homozygous recessive in order to happen. However, even in heterozygous pairs, carriers of the gene can experience sickle cell disease in extreme oxygen depletion levels. In fact, the alleles are really codominant; there are both irregular and regular hemoglobin in the blood in heterozygous carriers.
Why is sickle-cell disease considered an example of pleiotropy?
Because it protects people against malaria, as well as having numerous consequences to the body.
What group of people is sickle-cell disease most common in?
People of African descent. About 1/10 African-Americans carry the gene.
Why does sickle-cell disease persist?
Because in protecting against malaria, it allows those with it, in Africa, to reproduce more than those without it.
End of 9.13 Question: Why is the sickle-cell trait considered codominant at the molecular level?
Codominance means that both traits are expressed; a carrier for the sickle-cell allele produces both normal and abnormal hemoglobin.
