POPULATION GENETICS Flashcards
WHAT IS THE BASIS OF THE GENETIC DIFFERENCES?
mutations, selection, degree of reproductive isolation
DEFINE POPULATION
a group of individuals of the same species, which contribute to a common population gene pool
FREQUENCY OF A TRAIT FORMULA
Frequency = number of individuals with trait (or disease) / total number of individuals in a population
HOW MANY RACES IS THE HUMAN POPULATION DIVIDED INTO?
in 3 races → they are genetically and phenotypically different
EG: negroid, caucasoid, mongoloid
-> divided into ethnic subgroups
NAME SOME EXAMPLES FOR DIFFERENCES AMONG POPULATIONS
- 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
WHAT DOES THE HARDY WEINBERG LAW SAY?
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
WHAT IS THE RELATIONSHIP BETWEEN THE HARDY WEINBERG FREQUENCIES?
p + q = 1
WHAT IS THE FREQUENCY OF THE GENOTYPES OF THE HARDY WEINBERG?
p^2 + 2pq + q^2 = 1
HOW THE HARDY WEINBERG IS CALCULATED
WHAT IS THE FREQUENCY OF THE AUTOSOMAL RECESSIVE DISORDER?
q^2
WHAT IS THE FREQUENCY OF THE AUTOSOMAL DOMINANT DISORDER?
p^2 + 2pq
EXPLAIN THE HARDY WEINBERG THEORY FOR X-LINKED GENES
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
EXPLAIN THE HARDY WEINBERG THEORY FOR 3 ALLELES.
P + Q + R = 1
(P + Q + R)^2 = 1
WHAT ARE THE CONDITIONS NECESSARY FOR HARDY WEINBERG EQUILIBRIUM?
-random mating
-no migration
-balance between mutation and selection
-large population
WHAT ARE THE DISTURBANCES OF THE HARDY WEINBERG EQUILIBIRUM?
-non random mating
-eugenics
-migrations
-mutations & selections
-small populations
GIVE 3 EXAMPLES OF NON-RANDOM MATING.
-consanquinity
-stratification of population
-assortative mating
EXPLAIN ASSORTATIVE MATING
free to choose mate
-> based on phenotype and preferences
-> share the same allele
EXPLAIN STRATIFICATION OF POPULATIONS
mating limited to a pool of certain individuals within a subgroup -> ethnic groups
EXPLAIN CONSANQUINITY
the fact of being descended from the same ancestor
-> selective pairing
-> increased risk of autosomal recessive diseases
-> decrease of heterozygotes and increase of homozygotes
WHAT DOES F * Q MEAN?
- F * q = risk of being affected by AR disease in a marriage btw relatives
- F = interbreeding coefficient
- q = frequency of alleles in population
EXPLAIN MIGRATION
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)
EXPLAIN FOUNDER EFFECT
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
EXPLAIN GENETIC DRIFT
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)
EXPLAIN THE CONCEPT OF EUGENICS
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)
DEFINE SELECTION
mechanism which ensures that the mutation in not inherited and passed through generations
→ mutated allele is lethal (leads to death or sterility)
WHAT IS THE RELATIONSHIP BETWEEN ALLELE FREQUENCY, MUTATION FREQUENCY AND SELECTIVE PRESSURE IN A POPULATION?
allele frequency in population = mutation frequency + selective pressure
DEFINE FITNESS
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)
EXPLAIN LETHAL AD MUTATION
high selective pressure (fast selection), because homozygotes and heterozygotes die
EXPLAIN LETHAL AR MUTATION
hidden mutation of heterozygotes – slow selection
EXPLAIN LETHAL XR MUTATION
1/3 of men lost in each generation
→ frequency of alleles maintained by new mutations
EXPLAIN THE HETEROZYGOTE ADVANTAGE
- 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)
WHAT IS A LETHAL ALLELE?
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
