Genetics Flashcards
What type of dominance is ABO blood type an example of? Explain
Codominance, where both alleles are equally dominant.
Red blood cells have different sorts of antigens or agglutinogens on their plasma membrane.
Two antigens: A and B
If there are no antigens, it is O
Why are type O blood types universal donors?
Their red blood cells don’t have any antigens (A or B) on them, so host antbodies will not cause them to clump (agglutinate)
What blood type can receive blood from all types?
AB, because they have neither A nor B antibodies
What is responsible for the + or - designation of blood types?
Rh factors, which are coded by different genes at different loci from the A and B antigens. They are either present, or not present (present in 85% of the population)
What is linkage? (in regards to independent assortment)
Two traits located far apart on a chromosome are more likely to cross over and thus assort independently, as compared to two traits that are close. The propensity for some traits to refrain from assorting independently is called linkage.
What is a Barr body?
A condensed, inactivated X chromosome in every cell of a female’s body
Give the genotypic proportions for a monohybrid cross and a dihybrid cross:
Monohybrid cross (eg. Aa vs. Aa) = 1:2:1
Dihybrid cross (eg. AABB vs. aabb) = 9:3:3:1
Give the criteria which must be met for Hardy-Weinberg equilbrium (5)
- Random mating
- No mutations
- No genetic exchange with other populations
- Large population
- No selection pressures
Assuming defective Hormone X response is X-linked, which children of an affected male will most likely be unable to respond to hormone X?
Assume that females are never observed to be affected.
- None of the males
- None of the females
A punnett square (assuming mum is XX - both wild type) gives the following genotypes:
xX, XY, XY and xX
Only xX genotypes carry the allele, but the passage tells us that females do not exhibit the defective hormone response.
Hemophilia, a disease in which the time required for blood to clot is greatly prolonged, is determined by a sex-linked gene. Suppose a man with normal blood clotting marries a woman with normal blood clotting, whose father was a hemophiliac. If this couple has three sons, what is the probability that hemophilia will be transmitted to all three of them?
The probability of a son receiving the hemophilia gene and being a hemophiliac is 1/2. The cumulative probability of all three sons inheriting the hemophilia gene would be the product of the individual probabilities, or 1/2 x 1/2 x 1/2 = 1/8.
1/8 is the answer
Suppose that in a randomly mating population of mammals, 160 of its 1,000 members exhibit a specific recessive trait that does not affect viability of the individual. How many individuals in this population are heterozygous carriers of the gene that causes this trait?
480
The number of individuals carrying the described trait is 480. The gene frequency of the recessive trait, q, can be ascertained by taking the square root of 16/100 or .4. Given this frequency, the frequency of p must be 1.0 - .4 = .6. According to the Hardy-Weinberg law, the frequency of carriers is thus given by 2 pq or 2 X .4 X .6 = .48 or 48%. 48% of 1000 = 480.
Consider an organism that has three pairs of chromosomes, AaBbCc, in its diploid cells. How many genotypically different kinds of haploid cells can it produce?
8
The number of different possible gametes that can be formed by diploid organisms as a result of independent assortment of chromosomes during meiosis can be calculated using the formula 2^n, where n is the haploid number of chromosomes. In this case, the haploid number is 3, making the number of different haploid cells 2^3 = 8.
True or false, a sex linked disease, regardless of being linked to X or Y ALWAYS occurs more often in men?
True
Double stranded DNA can adopt one of three helical conformations depending on the nucleotide makeup of the molecule and the amount of hydration. The nucleotide base pairs in a DNA helix are arranged like steps in a spiral staircase, each one is rotated a few degrees from the previous base pair.
In investigating the properties of a strand of DNA, researchers determined that there were 12 nucleotide base pairs for every complete 360 degree turn of the helix. The conformation of the DNA strand was:
Z, nor A or B
If there are 12 base pairs for every 360 degree turn of the helix, then each one must take up 30 degrees. This amount of rotation is almost identical to that of conformation Z, with an average twist of 29.9 degrees.
A: 33 degrees
B: 36 degrees
Consider a diploid organism with a parent cell that is heterozygous (-/+), what is the expected phenotypic ratio for the diploid’s products of meiosis?
2 wild type
2 mutant
This question would be relevant for organisms that reproduce like S. cerevisiae. Because the daughter cells will be haploid (meiosis) there is no concept of dominance. First division would give a - cell and a + cell, than two - cells and two + cells.
