Topic 8

Question 1

allele

Answer 1

different forms of the same gene

Question 2

why are ratio of offspring phenotypes not as we expect

Answer 2

small sample size
random process
genes are linked (autosomal linkage)
organisms escape/ die

Question 3

crossover value

Answer 3

cov = (number of recombinant offspring )/(total number of offspring) x 100

Question 4

gene pool

Answer 4

all the alleles of all the genes of all the individuals in a population at any one time

Question 5

allele frequency

Answer 5

proportion of a particular allele out of the total number of alleles in the population

Question 6

genetic diversity

Answer 6

biodiversity within a species, total number of different alleles in a population

Question 7

selection

Answer 7

organisms better adapted to their environment have advantageous alleles which become more common in the population so change in allele frequencies

Question 8

adaptive radiation

Answer 8

different selection pressures cause adaptation to environment e.g. lack of food, water, predation, antibiotic

Question 9

stabilising selection

Answer 9

favours the mean, maintains continuity in a population by reducing variation/ preserving phenotypes in a population due to stable conditions
E.g. mortality of babies due to their birth weights

Question 10

directional selection

Answer 10

favours organisms that vary in one direction from the mean due to environmental pressure, changes the phenotype of the population and allele frequency
E.g. resistance to bacteria to penicillin

Question 11

disruption selection

Answer 11

favours organisms on both ends of the mean, increasing genetic diversity in the population due to diverse conditions resulting in evolution of a new species
E.g. salmon size and competition for food/ predation

Question 12

genetic drift

Answer 12

random changes to gene pool of a population by chance of random selection of alleles available to be passed onto offspring, not due to alleles being (dis)advantageous

in a small population random selection can result in some alleles are entirely lost and genetic diversity is reduced

Question 13

population bottlenecks

Answer 13

effect of a (series of) events that dramatically reduces the size of the population, decreasing the gene pool, resulting in large changes in allele frequencies and reduction in genetic diversity

Ecological events e.g. earthquakes, fires, floods

E.g. Northern elephant seals almost hunted to extinction, reducing genetic diversity, small surviving populations contain allele frequency unrepresentative to original population, so some alleles are over represented and some are removed completely

Question 14

Founder effect

Answer 14

loss of genetic diversity when a small group of the population are isolated, forming a new population (founder population) with unrepresentative allele frequencies to original population

mutation may occur in founder population or a different more common allele to original due to different environment results in different allele frequencies

Question 15

Hardy-Weinberg equation

Answer 15

p^2+2pq+ q^2=1
p+q=1 = total number of alleles

The proportion of dominant and recessive alleles of any gene in a population remains the same, as long as certain conditions are met
o No mutations
o No immigration or emigration (isolated)
o All alleles are equally likely to be passed on (no selection pressure)
o Large population
o Mating is random