Week 7: Questions Flashcards
Dr. Allsion noticed that in lowlands and wet areas there was a higher presence of mosquitos and there was a higher incidence of the sickle cell trait, whereas in highlands and dry areas there was a lower presence of mosquitos and lower incidence of the sickle cell trait
Hypothesis: the sickle cell trait provides resistance against the malaria parasite
Dr. Allison tested his hypothesis in three studies
- Used participants that were involved in a malaria drug trial by using their blood sample
- Found that 14/15 of the participants who did not have the sickle cell trait did get malaria, whereas the 1/15 participant who did have the trait did not get it
- Although these results were consistent with the hypothesis, Dr. Allsion realized that those who lived in mosquito infested areas may have built an immunity to P. falciparum
- To address the issue with the previous study, Dr. Allison collected blood samples from children in the area and looked examined for the presence/absence of the sickle cell trait as well as if it contained P. falciparum
- Found that P. falciparum was present in 28% of children who had the sickle cell trait, but 46% of children who didn’t have it
- The children without the trait also had a higher number of parasites present
Collected blood samples from individuals from 30+ tribes across Africa
- Found that in all locations, the sickle cell trait was rare in locations where malaria was absent and common where malaria was an issue
What is the function of hemoglobin in your body?
To carry oxygen in red blood cells
Sickle cell disease is the result of defective Hemoglobin proteins (HbS rather than the normal HbA). What causes HbS to appear in a person?
HbS forms long filaments when oxygen levels are low, which deforms the cells
A person can be a “carrier” of sickle cell but not have the disease. How is this possible?
This is because the sickle cell trait is inherited, if an individual inherits one normal gene and one sickle gene, they are only a carrier
Why do some groups of people in Africa have a relatively high percentage of individuals with sickle cell disease?
This is because it is an evolutionary trait that they developed in response to malaria
Electrophoresis
is a method used to separate mixtures of molecules (ie. proteins, DNA, RNA)
Pauling found that:
Two types of haemoglobin are different chemically
Sickling occurs in low oxygen
The type of hemoglobin in an individual is related to genetics
The cause of the disease could be traced to an alteration in the molecular structure of a protein (in HbS the amino acid in position 6 is valine instead of glutamic acid like it is in HbA, which results in the abnormal protein that causes a disease)
In electrophoresis which type of molecules will move the farthest from the well?
The smaller DNA segments
Why do molecules move through the gel in electrophoresis?
Because the gel is negatively charged so the DNA will migrate towards the positively charged end.
If pangenesis was how inheritance worked, and you crossed a white flower with a red flower, what colour would the offspring be?
It would be pink because it would take the white colour and red colour “seed” from each flower and blend this characteristic in the offspring
Meiosis
Meiosis sorts genes into gametes which fuse upon fertilization, when genes from the mother and father are brought together again
Mendel’s Rules
- Genes can come in more than one form (allele)
- Ex. gene for hemoglobin can be a normal or sickle cell allele, which encodes for HbA or HbS, a pea flower colour gene can be either a purple or white allele
- The alleles of a gene sort individually into gametes during meiosis
- Ex. a person who is a carrier of sickle cell disease will make gametes and 50% will have normal hemoglobin allele while the other 50% will have the sickle cell allele, a pea with a purple allele and white allele would produce gametes each possessing each of these alleles
- A trait is exhibited as dominant or recessive
- Ex. pea flower colour is a trait that exhibits dominant/recessive relationship between the purple and white alleles. Purple is the dominant trait (the one seen when both alleles appear together). When purple and white are present together, the two different alleles produce a flower as purple as one developed by a plant with two purple alleles because white is not seen (recessive trait)
The presence of horns on Hereford cattle is controlled by a single gene. The hornless condition (H) is dominant over the horned (h) condition. A hornless cow was crossed repeatedly with the same horned bull. The following results were obtained in the offspring:
8 hornless calves
7 horned calves
What are the alleles of the parents?
Hh
In human beings, brown eyes are dominant over blue eyes. Suppose a blue-eyed man marries a brown-eyed woman whose father was blue-eyed. What proportion of their children would you predict should have blue eyes?
25%
