Populations

Question 1

Def of population

Answer 1

All individuals of same species, that live in same area ata same time, and can interbreed

Question 2

what do population genetics study

Answer 2

. interactions of alleles + genes in pop
. distribution of allele freq in pops
. change of allele frequency under influence of natural selection, mutation, gene flow + genetic drift

Question 3

define gene pool, natural selection, genetic drift, bottleneck effect, founder effect, gene flow, allele fixation

Answer 3

• gene pool - all alleles at all loci in pop
• NS - survival + reproduction of individuals in pop sue to differences in traits
• Genetic D - changes in gene pool of small pop due to chance eg tornado, earthquake,
  DRIFT CAUSES BOTTLENECK AND FOUNDER
• Bottleneck - pop undergoes drastic reduction in size due to chance ( cause of Genetic D)
• Founder - small group of individuals become separated from larger pop. (cause of genetic D)
• Gene flow - movement of genes btw pops. gain/loss of alleles from pop due to migration of individuals or transfer of gametes. gene flow is a result of migr.
• Allele F - when 1 allele of gene becomes the only allele, while alternatives eliminated from pop

Question 4

Phenotype frequency def
how to calculate

Answer 4

proportion of individuals in pop that has specific phenotype.

. num of individuals wth given genotype ÷ total invidualsin pop

AA+Aa/AA+Aa+aa or aa/AA+Aa+aa

Question 5

what is the sum of all phenotype freq for a trait.

Answer 5

1
PF is always btw 0-1

Question 6

Genotype Frequency def

Answer 6

proportion of individuals wth specific genotype in pop.

calculate: num of indiv wth phenotye ÷ total indi in pop

AA/AA+Aa+aa or Aa/…. or aa/…..

Question 7

how can GF be calculated directly

Answer 7

if genotype has its own phenotype (ie, incomplete dominance/ codominance)

MN blood group system - based on 2 Codominant alleles

Question 8

Allele frequency

Answer 8

proportion of copies of given gene in pop that is specific allele. shows how abundant particular allele is in pop.

calc: num of copies of given allele in pop ÷ total num copies of all alleles of this gene in pop.

( which is twice the num of individuals cos they diploid.)

Question 9

F(A) and F(a) calculations

Answer 9

F(A) = F(AA) + 0.5F(Aa)

F(a) = F(aa) + 0.5F(Aa)

Question 10

what do you do when 2 events are independant of eachother? then when an event occurs in 2 incompatible ways.

Answer 10

independant - probability that both occur is PRODUCT of their probs
Incompatible - probabiluty is SUM of their probs

Question 11

what is relative frequency of an event

Answer 11

number of times its occured ÷ total num it could hv occured

when a statistical event is repeated many times, its relative frequency approximates its theoretical probability.

Question 12

What is hardy weinberg law. what are the conditions

Answer 12

p^2 + 2pq + q^2 = 1
. large pop
. no mutations
. no migrations
. random mating

Question 13

Applicationn of HW

Answer 13

prediciting allele + genotype freq in cases of complete dominance, when its impossible to find directly

Question 14

what are the forces of evolutions ( changes balance of genotypes + breaks down HW rule)

Answer 14

mutations, migrations, non random mating, isolation, natural selection, genetric drift

Question 15

Gentetic drift

Answer 15

random fluctuations of allele freq due to chance events. Its an example of sampling error
. important in small pops as can eliminate alleles, and leave only 1.
. produces evolutionary change but not adoptive ( the poplation doesnt become more adapted due to it)

Question 16

what is bottleneck effect

Answer 16

pop is greatly reduced (ie hurricane kills most in a pop). who lives/dies is unrelated to phenotype

(humans) - when small group move to new teriiroty. the new pop differ from og as they share same genes but the balance of gene varients in each pop differ

Question 17

what is founder effect

Answer 17

few individuals leave their pop + found a new one (eg colonise an island). chnages in gene pool
. not representative of og pop
. most common = loss of alleles, but also possible for a rare mutant allele to increase its freq

example = amish community was founded by small num of colonists. these colonists had gene for polydactyly. since amish quite isolated and few outsiders join, polydactly much more common in amish.

Question 18

What is migration/ gene flow

Answer 18

. when individualsmove + breed in a new pop (+ gives their genes in that pop)
. also occurs by HYBRIDIZATION - individuals from 2 separate pops breed, their offspring carry genes from 1 pop to another.

increases variability of gene pool. Also unites pops, making a common gene pool of entire species.

Question 19

What is natural selection

Answer 19

when idividuals who hv certain genes are more fit to mature and reproduce than those without those genes, the freq of these genes will increase.

• only eolutanary force that can cause adaptive evo

Question 20

what does NS include

Answer 20

1. differential viability
2. differential fecundity (ability to produce an abundance of offspring)

eg, vit D synthisized in UV exposed human skin. over the years, this need to make Vit D was evo driver for skin lightening in humans.

Question 21

how to measure natural selection

Answer 21

. relative fitness (w) + selection coefficient (s)
. They characterize success of indiv with given phenotype
. success measured by avg num surviving offspring left by individual having the genotype. This lifetime reproductive success = absolute fitness
. AF dependant on changes to pop size tho

so we do:

af of each genotype ÷ af of best genotype
gets us relative fitness

. best genotype is w=1, genotype thats lethal/ 100% infertility is w=0

. s = 1 - w: selection coefficient measures how strongly selection acts against given genotype.
. higher s is worse. (s=1) best genotype s= 0

Question 22

how does selection change allele freq for dom + recces

Answer 22

dominant allele cant be hidden so selection against it is very effiecient + eleiminates fromm pop

selection against reccessive efficient at first, but slower after allele freq drops, due to larger prop of the recces allele is protected i herterozygotes.

this means NS alone cant eliminate R alleles, just reduces.

IF S=1 DOMINANT ALLELE ELIMINATED IN NEXT GEN
IF S=1 RECESSIVE ALLELE NEVER ELIMINATED AS PROTECTED IN HETEROZYGOTES

Question 23

eg of selection = Duffy null. explain

Answer 23

Duffy gene encodes cytokine receptor used by plasmodium vivax to invade erythrocytes.

duffy null mutations give resistance to vivax malaria. Its fixed in sub Saharan Africans where malaria is common (like in madagasgar) + absent in others.

frequency of duffy null of madagascans is >0.7 usually its 0.5.

its selection = 0.066. protects against the malaria

Question 24

What is importance of mutations

Answer 24

evolution depends onit as it makes new alleles.
allows for natural selection.

. they rare but occurs each generation. along wth genetic drift, non coding seq evolve faster than coding, and not needed genes accumulate mutations + turn into PSEUDOGENE.

Question 25

what is mutation rate

Answer 25

μ - freq of norm allele to turn into mutant allele per gamete. (longer genes mutate more often)

. too many mutations can lead to disease/ birth defects
. mutation rate increases when DNA replic or repair is disturbed.
. smaller pops less able to compensate for genetic change that increase μ.

Question 26

what are some mutation rates of diseases

Answer 26

hemophilia A = 2.5 x 10^4
duchenne muscular dystrophy = 1 x 10^4
. avg rate of nucleotide substitutions is 10^-8 to 10^-9 per generation

Question 27

what happens when mutation is deleterious

Answer 27

the 2 processes will act against each other. Each gen, selection will reject some mutant alleles, but mutation will produce new ones.

overtime the mutant allele reaches equlibrium freq

Question 28

what is the cause of ore prevelent deleterious recessive alleles.

Answer 28

selective adv of heterozy over homozy for the normal allele
- eg sickle cell anemia (s = 0.76). but in some parts allele F = 18% (μ >2%).
- heterozygotes turn out to be resistant to falciparum malaria

Question 29

Non random mating and its types

Answer 29

indivi hv mating prefrences so dont randomly mate in pop. changes genotype frequencies.

1. ASSORTATIVE mating - individuals choose partners based on phenotype similarity. can be positive or negative (similar/disimilar). positive increases homozygosity, negative heterozygosity.
2. INBREEDING - mating btw individuals related by ancestry (common in small isolated pops)

Question 30

example of positive assortive mating

Answer 30

Deafness - deaf people communicate by sign lang instead of speech.
deafness phenotype has frequncy higher than q^2 as more homozygotes.

connexin gene cause of hereditary deafness

Question 31

mating with a relative - what does it do

Answer 31

. affects many loci cos partners share many genes from common ancestors
. extreme - self fertimlisation in hermaphrodites (produces gametes by meiosis). Partner wth SAME GENOTYPE AT EVERY LOCUS. heterozygosity decreases (50% reduct per gen)

. inbreeding increases reccessive alleles in homo. it often diminishes fitness = inbreeding depression

Question 32

examples of preventing inbreeding

Answer 32

• lions push male cubs out of pride when they mature so they dont breed with their sisters.
• self incompatibility in some plants

Question 33

Relatedness coefficient ( coeff of relationships)

Answer 33

r - meausres how related 2 individuals are. if unrelated r = 0

. calculated by the fact that the prob for each allele transferred from parent to child = 0.5.
. pedigree diagram used (pg 39)

Question 34

Inbreeding coefficien

F= 1/2 x rleatedness coeffivient

Answer 34

F- prob that any locus of individual has 2 identical alleles by descent.
F only measured if parents are relatives. if unrelated, F of progeny = 0

in isolated pop, at some point individuals run out of unrelated mating partners so everyone acquires some inbreeding coefficient.

Question 35

Inbreeding coefficient

F=0.5x2

Answer 35

consanguineous = related

Full sibls hv relatedness r = 1/2, + their offspring hv an inbreeding coefficient F =1/4. This means they are identical by descent at one-quarter of their loci.

If any of these loci involve recessive mutant allele that affects pre- or perinatal health, mortality of children will be higher
reduced health of inbred children = inbreeding depressions

• prevelent in spanish kings habsburg dynasty

Question 36

what are quantative traits

Answer 36

. determined by interaction + additive effects of multiple
genes + environmental factors. Also called polygenic /
multifactorial.
. doesnt follow mendelian inheritance pattern
. example of this trait = height, weight, skin colour, predisposition to heart diseases.

Often, trait which is quantitative in the normal population has a pathology which is
qualitative (e.g. normal height vs. dwarfism, normal skin color vs. albinism).

Question 37

Model of inheritance of quanitative traits pg 57

Answer 37

normal distribution wth intermediate phenotype the most common.
. Cos more intermediate the phenotype, the greater the number of genotypes that can cause it.
. The more genes involved, more phenotypic classes occurs.
. The more genes involved, the less the distinction between classes.

Question 38

Normal distrubution

Answer 38

The spread ND controlled by the standard deviation, σ
(s.d.). The smaller the sd the more concentrated the
data. For some traits, the entire range
of the normal curve is normal. For
others (e.g. weight), one /both
extremes are abnormal (pathological).
For many quantitative traits, the
distribution is “skew-normal”, i.e. more
or less asymmetrical.