Population Genetics

Question 1

Solve. If A is the wild type allele and a is the cystic fibrosis allele and the frequency of cystic fibrosis (aa) is 1/2500, what’s carrier frequency?

Answer 1

q^2 = (1/2500), q = (1/50)
so p = 49/50, and you can plug into 2pq to get frequency of carrier

Question 2

What are two ways to find probabilty?

Answer 2

If looking at the likelihood of two separate events occurring you add p(A) + p(B) = 1. if you want to see the outcome of two of the same event you multiple ex. chances of mom having two miscarriage: 1/6 x 1/6 = 1/36 = 3%

Question 3

Bayes theorem

Answer 3

1. there’s an initial probability based on circumstance
2. additional info excludes some of the possible circumstances
3. combining both gives you a posterior probability
   Ex. a child is born two two carrier parents of autosomal recessive disorder. What is probability he/she/ they does not have the disease? originally = 2/4, but since there’s information that the child doesn’t have the disease, the posterior probability is 2/3

Question 4

What are the 5 types of genetic testing?

Answer 4

1. Prenatal = examine fetal tissue, or use ultrasound/MRI to give parents an informed choice.
2. Newborn screening = not in all states looks for things like PKU, hemoglobinpathies, congenital problems by looking for common disease, not expensive procedure, and non-invasive
3. Carrier screening = predicts risk and helps make informed decision ex. sickle cell in african americans, or tay sachs in ashkenazi jews
4. Presymptomatic - individuals with age dependent muation can get pretested
5. Direct consumer testing - sending ancestry

Question 5

What are rules of heterozygote screening?

Answer 5

should be voluntary, with consent, confidential, adequate counseling, and equal access

Question 6

Presymptomatic Diagnosis

Answer 6

for age dependent disorders like inherited cancer and Huntington’s disease, individuals can be tested for disease causing mutation before clinical symptoms. This can aid in reproductive decisions, and improve health surveillance.

Question 7

What can you use to determine environment on a trait?

Answer 7

Monozygotic twin studies. Since they are identical, any differences between the pair should be due to environment. The more similar the traits of the twins, the higher the concordance.

Question 8

heritability

Answer 8

% of population variation in a trait; (h) = Cmz - Cdz

Question 9

What’s linkage analysis?

Answer 9

when two close loci are inherited together. Single nucleotide polymorphisms can be used as markers to help find disease causing alleles. This connects with linkage equilibrium because it is normal when loci are inherited independently, but we get disequilibrium when their linked. GWAS looks at these linkages via case studies.

Question 10

What’s linkage analysis?

Answer 10

when two close loci are inherited together. Single nucleotide polymorphisms can be used as markers to help find disease causing alleles. This connects with linkage equilibrium because it is normal when loci are inherited independently, but we get disequilibrium when their linked. GWAS looks at these linkages via case studies.

Question 11

haplotype

Answer 11

all alleles on a chromosome

Question 12

What can lead to missing heritability?

Answer 12

If variants are too minor, rare, the environment gets involved, or epigenetics.

Question 13

What deviates from Hardy Weinberg?

Answer 13

Natural selection = overtime favors mutations that increase fitness Ex. Duschene’s selected against, but still around because of new mutations. Another example is in balanced polymorphism, where both homozygotes are selected against (malaria/sickle cell). Genetic drift = small population are impacted greatly by small allele changes, Ex. founder affect - someone forming their own population or Bottle neck - only a few in population survive.