Genetics-Population Studies Flashcards
Risk that II-4 is affected?
01/04/14
Risk that III-1 is affected? III-2?
III-1: 1/2. III-2: low (spontaneous mutation rate)
Risk that III-3 is affected in this X-linked disorder?
Since II-4 is an obligate heterozygote, there is 50% chance of transmitting X chromosome and 50% chance of being male. 1/2 * 1/2 = 1/4.
What is population genetics?
Study of allele frequency in a population and factors that influence the frequency
Hardy-Weinberg equilibrium “p”.
For an autosomal locus with two alleles (A and a), it is the frequency of allele A.
Hardy-Weinberg equilibrium “q”.
For an autosomal locus with two alleles (A and a), it is the frequency of allele a in the population.
Hardy-Weinberg equilibrium
p + q = 1
Hardy-Weinberg equation fo an autosomal locus with two alleles A and a?
p^2 + 2pq + q^2 = 1.
Cystic fibrosis (CF) is an autosomal recessive disorder. It affects 1/2,500 whites of northern and central European origin. What is the frequency of the mutant CF allele? What is the carrier frequency?
Mutant allele (aa) frequency: q^2 = 1/2,500. So sqrt(1/2,500) = 1/50. Carrier frequency (Aa = 2pq): p = 1-q = 49/50. 2pq = 2(49/50)(1/50) = 1/26
II-3 has phenylketonuria (PKU), an autosomal recessive disorder present in 1/10,000 children. What is the risk for III-1?
Risk of II-4 of being a carrier is 2/3. Risk of II-5 being a carrier is 2pq. q^2 = 1/10,000. q=sqrt1/10,000 = 1/100. p = 1 - q = 1 - 1/100 = 99/100. 2pq = 2(99/100)(1/100) = 1/50. The risk of both II-4 and II-5 being carriers is 2/3 * 1/50. The risk of III-1 getting the homozygous trait (2/3)(1/50)(1/4) = 1/300.
Alterations of Hardey-Weinberg calculations if autosomal dominant? If X-linked recessive?
AD = Homozygotes are rare and are excluded = 2pq. X-linked recessive = in affected males the disease frequency is = allele frequency and = q. In carrier females = 2pq.
What is the ratio of affected males to affected females in X-linked recessive disorders?
(q/q^2) = 1/q
Hemophilia A is an X-linked recessive disorder found in 1/5,000 males. What are the frequencies of carrier and affected females?
q = 1/5000, p = 1 - 1/5000. Carrier frequency = 2q = 2/5000 = 1/2500. Affected females = a^2 = (1/5,000)^2 = 1/25,000,000.
Hemophilia A is an X-linked recessive disorder found in 1/5,000 males. What is the ratio of affected males to affected females?
q/q^2 = 1/q = 5000.
Assumptions of Hardy-Weinberg?
Large population (in small populations you have founder effect & genetic drift), random mating (assertive mating and consanguinity), and no mutations (10^-5), migration (genetically links 2 separate populations) or selection (affects frequency of alleles).
An African American couple with a normal family history wants to know their chance of having a child with sickle cell anemia. The incidence of sickle cell trait is 1 in 8 for African Americans. The risk in this case is?
Trait means heterozygote. For the child to be affected both parents have to be carriers. The chance of each parent being a carrier is 1/8. The chance of the child being a homozygote is 1/64 and the total risk is 1//64 * 1/4 = 1/256.
A woman who married her first cousin wants to know the risk of having a child with cystic fibrosis because her grandmother, who is also her husband’s grandmother, died of cystic fibrosis. Her risk is?
1) Calculate the chance that the children of the grandmother have inherited the mutant allele, 2) Then you need to calculate the risk that their children are carriers 3) Calculate the risk of the children being homozygous
The frequency of Tay-Sachs carriers among Ashkenazi Jews is ~1 in 30. Whites of Western European descent are affected much less frequently with approximate disease prevalence of 1 in 360,000. If a mother is an Ashkenazi Jew and a father is a white from Western Europe, what is the chance that a child of this union will have Tay-Sachs?
1) Calculate the risk of being a carrier with Weinberg. 2) Risk of both being carriers 3) Risk of child being homozygote
Individuals with achondroplastic dwarfism have about 80% fewer viable offspring than do normal persons, but the incidence of achondroplasiaseems to have remained constant for generations. These observations imply?
Decreased fitness (fewer viable offspring), negative selection (fewer progeny) and high mutation rates (disease incidence remains the same)
A murder suspect has been typed for three polymorphic genes, and his alleles match those of the evidentiary sample. He is a heterozygote for the first two genes and a homozygote for the third. The allele frequencies for the first gene in the general population are 0.05 and 0.10. For the second gene, they are 0.07 and 0.02. For the third gene, the allele frequency in the general population is 0.08. What is the probability that a random individual in the general population would match the evidentiary sample?
1) Find the chance of being a random carrier for 1st gene 2) Find chance of being a random carrier for 1st gene 3) Chance that he would be homozygote for 3rd gene 4) Chance that random person in population has all 3 genes.
The table shows concordance rates for two disorders in monozygotic twins, dizygotic twins and siblings. Which one of the following causative patterns describes disorder A? Disorder B?
Disorder A is almost purely genetic and probably autosomal recessive. Disorder B is mostly environmental with a prenatal environmental role.
