POPULATION GENETICS

Question 1

WHAT IS THE BASIS OF THE GENETIC DIFFERENCES?

Answer 1

mutations, selection, degree of reproductive isolation

Question 2

DEFINE POPULATION

Answer 2

a group of individuals of the same species, which contribute to a common population gene pool

Question 3

FREQUENCY OF A TRAIT FORMULA

Answer 3

Frequency = number of individuals with trait (or disease) / total number of individuals in a population

Question 4

HOW MANY RACES IS THE HUMAN POPULATION DIVIDED INTO?

Answer 4

in 3 races → they are genetically and phenotypically different
EG: negroid, caucasoid, mongoloid
-> divided into ethnic subgroups

Question 5

NAME SOME EXAMPLES FOR DIFFERENCES AMONG POPULATIONS

Answer 5

• ALBINISM in some Indian tribes
• SICKE CELL in Africa
• BETA THALAESSMIA around Mediterranean sea
• CYSTIC FIBROSIS rare in Caucasians (except Finland)
• high frequency of 20 RARE DISEASES in Finland -> XR CHOROIDEREMIA
• HUNTINGTONS and PORPHYRIA VARIEGATE in South Africa

Question 6

WHAT DOES THE HARDY WEINBERG LAW SAY?

Answer 6

it says, that gene and genotype frequencies remain the same across generations, IF frequency of alleles does not change. (e.g. 10% of population is heterozygote → it can prove that this frequency isnt changing)

• assumption that there are only two alleles in the population:
  
  • Standard allele A
  • mutated allele a
• frequency(A)= p , frequency(a)= q

Question 7

WHAT IS THE RELATIONSHIP BETWEEN THE HARDY WEINBERG FREQUENCIES?

Answer 7

p + q = 1

Question 8

WHAT IS THE FREQUENCY OF THE GENOTYPES OF THE HARDY WEINBERG?

Answer 8

p^2 + 2pq + q^2 = 1

Question 9

HOW THE HARDY WEINBERG IS CALCULATED

Answer 9

Question 10

WHAT IS THE FREQUENCY OF THE AUTOSOMAL RECESSIVE DISORDER?

Answer 10

q^2

Question 11

WHAT IS THE FREQUENCY OF THE AUTOSOMAL DOMINANT DISORDER?

Answer 11

p^2 + 2pq

Question 12

EXPLAIN THE HARDY WEINBERG THEORY FOR X-LINKED GENES

Answer 12

MALES: P + Q = 1
-> frequency of mutant allele q = frequency of affected males
-> frequency of normal allele p = frequency of normal males

FEMALES: P^2 +2PQ + Q^2 = 1

Question 13

EXPLAIN THE HARDY WEINBERG THEORY FOR 3 ALLELES.

Answer 13

P + Q + R = 1
(P + Q + R)^2 = 1

Question 14

WHAT ARE THE CONDITIONS NECESSARY FOR HARDY WEINBERG EQUILIBRIUM?

Answer 14

-random mating
-no migration
-balance between mutation and selection
-large population

Question 15

WHAT ARE THE DISTURBANCES OF THE HARDY WEINBERG EQUILIBIRUM?

Answer 15

-non random mating
-eugenics
-migrations
-mutations & selections
-small populations

Question 16

GIVE 3 EXAMPLES OF NON-RANDOM MATING.

Answer 16

-consanquinity
-stratification of population
-assortative mating

Question 17

EXPLAIN ASSORTATIVE MATING

Answer 17

free to choose mate
-> based on phenotype and preferences
-> share the same allele

Question 18

EXPLAIN STRATIFICATION OF POPULATIONS

Answer 18

mating limited to a pool of certain individuals within a subgroup -> ethnic groups

Question 19

EXPLAIN CONSANQUINITY

Answer 19

the fact of being descended from the same ancestor
-> selective pairing
-> increased risk of autosomal recessive diseases
-> decrease of heterozygotes and increase of homozygotes

Question 20

WHAT DOES F * Q MEAN?

Answer 20

• F * q = risk of being affected by AR disease in a marriage btw relatives
• F = interbreeding coefficient
• q = frequency of alleles in population

Question 21

EXPLAIN MIGRATION

Answer 21

changes the frequency of alleles in a population by the slow diffusion of alleles from one population going into the gene pool of another population
(GEOGRAPHICAL BARRIER)

Question 22

EXPLAIN FOUNDER EFFECT

Answer 22

when a small group of individuals become isolated from a larger population and create a subgroup population changing the allele frequency of the original population
-> increased sensitivity to genetic drift, an increase in inbreeding, and relatively low genetic variation

Question 23

EXPLAIN GENETIC DRIFT

Answer 23

a random change in the allele frequency of a population due to a chance event
-> much more common in smaller populations for alleles to disappear
-> probability of receiving a mutated allele is always 50 %, however it does depend on chance if the allele will be inherited (the rule of chance suggests that there is the same probability of occurrence of the allele as there is of its disappearance)

Question 24

EXPLAIN THE CONCEPT OF EUGENICS

Answer 24

the study of how to arrange reproduction within a human population to increase the occurrence of heritable characteristics regarded as desirable

POSITIVE – positive traits are preferably reproduced (selective breeding of animals, plants)
NEGATIVE - elimination of unwanted genotypes (preimplantation/prenatal screening + abortion)

• reduces the selectivity and eases the inheritance of negative alleles to next generations (in other words – treatment
  works against selection; it does not improve the gene pool of population as it allows the reproduction of some diseases to next generations)

Question 25

DEFINE SELECTION

Answer 25

mechanism which ensures that the mutation in not inherited and passed through generations
→ mutated allele is lethal (leads to death or sterility)

Question 26

WHAT IS THE RELATIONSHIP BETWEEN ALLELE FREQUENCY, MUTATION FREQUENCY AND SELECTIVE PRESSURE IN A POPULATION?

Answer 26

allele frequency in population = mutation frequency + selective pressure

Question 27

DEFINE FITNESS

Answer 27

reproductive success
-> how well an organism is adapted to its environment

EG: ACHRONDOPLASIA

f = 0,2 (only 20% of effected have offspring – hard for them to find a partner)
s = 0,8 = 80 % forms as a new mutation (mutation in gametes of unaffected parents -> this maintains the stability of mutation in population)

Question 28

EXPLAIN LETHAL AD MUTATION

Answer 28

high selective pressure (fast selection), because homozygotes and heterozygotes die

Question 29

EXPLAIN LETHAL AR MUTATION

Answer 29

hidden mutation of heterozygotes – slow selection

Question 30

EXPLAIN LETHAL XR MUTATION

Answer 30

1/3 of men lost in each generation
→ frequency of alleles maintained by new mutations

Question 31

EXPLAIN THE HETEROZYGOTE ADVANTAGE

Answer 31

• sickle cell anaemia (malaria resistance)
• half haemoglobin is normal, half is abnormal
  → balanced polymorphism = selection in both directions (AA suffer from malaria, aa suffer from SCA)

Question 31

WHAT IS A LETHAL ALLELE?

Answer 31

cause the death of the organism that carries them
-> they are usually a result of mutations in genes that are essential for growth or development
-> not transmitted to the next generation