topic 8 : origins of genetic variaiton

Question 1

what are the sources of new genetic variation

Answer 1

• mutations
• crossing over (metaphase/anaphase 1)
• independant assortment (metaphase/anaphase 1 & 2)
• random fertilisation

Question 2

what is an allele

Answer 2

an alternative form of a gene

Question 3

what does it mean if an allele is dominant

Answer 3

an allele that is always expressed the phenotype, even if only one of them is present (heterozygous) - present in homoxygous and heterozygous

Question 4

what does it mean if an allele is recessive

Answer 4

an allele that is only expressed in the phenotype if two copies are present (homozygous) or if there is only one of the allele

Question 5

what does phenotype mean

Answer 5

the observable characteristics of an organism

Question 6

what does genotype mean

Answer 6

all the alleles present in a cell of an organism

Question 7

what does codominance mean

Answer 7

both of the alleles contribute to the phenotype without mixing

Question 8

what are multiple alleles

Answer 8

more than 2 possible versions of an allele

Question 9

what are chi squared tests used for

Answer 9

used when both variables are categorical (eg. height gourps at short/average/tall and gender male /female)

also normally used to check for autosomal gene linkage

Question 10

what does autosomal gene linkage mean

Answer 10

when 2 genes on the same chromosome are linked and inherited as if they were the same gene (eg. brown eyes and brown hair), not sex-linked

Question 11

what happens if the closer the 2 genes in autosomal link are located

Answer 11

then they are less likely to be separated during crossing over (the characteristic will be carried out)

Question 12

what does sex linked mean

Answer 12

they are on the X chromosome (this is why some health conditions are more common in men because they don’t have two X chromosomes -> only need one copy for it to be expressed

Question 13

what are two examples of sex linked conditions

Answer 13

haemophilia (absence of clotting factors)
red-green colourblindness

Question 14

why do frequencies of alleles change over time?

Answer 14

this is due to natural selection, which drives evolution

Question 15

why does natural selection occur

Answer 15

it occurs due to various seleciton pressures

Question 16

what is natual selection

Answer 16

process through which population of living organisms change and adapt

Question 17

what are the three types of natural selection

Answer 17

stabilizing, disruptive and directional

Question 18

what is stabilising natural selection

Answer 18

conserves phenotypes already existing in the population and hence reduces variation. selection is agains the extreme (more of the average features)

Question 19

what is disruptive natural selection

Answer 19

increased diversity in a population. common when conditions are varied and small sub population evolve different phenotypes based on these conditions. Selection is for extreme phenotype (completely opposite)

Question 20

what is directonal natural selection

Answer 20

normal natural selection which shows change from one phenotype to another which happens to be more advantageous for the envrionment

Question 21

what is a population bottle neck

Answer 21

a serious event that causes the population to reduce by at least 50% resulting in a dramtic change to the gene pool and allele frequencies and hence genetic diversity.

Question 22

what is genetic bottle neck?

Answer 22

sharp reduction in the size of a population due to environmental catastrophes like earthquakes, floods or diseases or human destruction like habitat destruction, overhunting or genocide

Question 23

what is the main difference between genetic bottlenecking and natural selection

Answer 23

genetic bottlenecking is like natural selection, but it happens much quicker and it is much more extreme
natural selection favours more advantageous characteristics and the population is bigger.

Question 24

what happens if there is less genetic diversity in a population

Answer 24

they are less likely to survive when met with different diseases or environmental conditions

Question 25

what is founder effect

Answer 25

loss of genetic variaitonw hen a small gorup of individuals are isolated and they form a new population- . they evolve n have allele frequencies tthat are not representative of the original pop.

Question 26

what is genetic drift

Answer 26

the allele frequencies are changing due to chance and not be a specific selection pressure.

Question 27

compare and contrast stabilising selection with disruptive selection

Answer 27

differences :
-n stabilising selection selects against the extreme phenotypes/disruptive selection selects against the mean/median phenotypes
- stabilising selection maintains 1 population/disruptive selection results in 2 distinct populations

similarities ;
- both change the frequency of alleles
- both select against phenotypes (reduces the variation)

Question 28

In 1994, there were only 20 gilbert’s potoroo individuals, 12 of which were in a captive colony.
a captive breeding programme was set up using :
- four adult females and one young female
- one adult male, two young males and one young male sill in its mother’s pouch.

explain why allele frequencies may cause problems in this population of potoroos

Answer 28

• population size is small due to the genetic bottle/founders effect
• gene pool is very small/genetic variation is reduced
• there is an increased likelihood of interbreeding which can cause problems.

Question 29

state what is meant by the term biodiversity

Answer 29

the variation of alleles in a gene pool

Question 30

explain why, in 2016, the genetic biodiversity of the lynx population in the area where they had been reintroduced was much lower than in the protected area

Answer 30

• only a small number was reintroduced so there is more interbreeding
• casuing a limited gene pool

Question 31

what are the conditions for the hardy weinberg equation

Answer 31

• no mutation
• random mating
• large population
• no migration (in or out))
• no selection pressure