Topic 8 Origins Of Genetic Variation

Question 1

what are three genetic reasons for genetic variation?

Answer 1

• mutations
• random independent assortment
• random fertilisation
• crossing over in meiosis

Question 2

what are two types of mutations?

Answer 2

• point mutation (change in bases)
• chromosome mutation

Question 3

what are 3 types of point mutations?

Answer 3

• deletion
• insertion
• substitution

Question 4

why do point mutations happen?

Answer 4

• random
• mutagens increase rate of mutations (eg chemicals, radiation)

Question 5

who is affected by somatic cell mutations?

Answer 5

only the individual

Question 6

who is affected by gamete mutations?

Answer 6

generations to come, passed onto offspring

Question 7

when does independent assortment happen during meiosis?

Answer 7

metaphase I and II

Question 8

when does crossing over happen during meiosis?

Answer 8

prophase I

Question 9

what are two types of chromosome mutations?

Answer 9

• translocation
• non disjunction

Question 10

what is translocation mutation?

Answer 10

when a chromosome breaks off and joins a non-homologous chromosome

Question 11

what is non-disjunction mutation?

Answer 11

when a homologous pair fail to separate correctly, some gametes have abnormal number of chromosomes

Question 12

what are two types of non-disjunction?

Answer 12

monosomy and polysomy

Question 13

what is an example syndrome of monosomy?

Answer 13

Turner’s syndrome

Question 14

what is an example syndrome of polysomy?

Answer 14

Down’s syndrome

Question 15

what is the chi squared equation?

Answer 15

(O-E)^2
———– (divide by)
2

Question 16

What is the definition of polygenic? 2 marks

Answer 16

• A characteristic influenced by 2 or more genes (1)
• in different loci (1)
• common to see variation in traits (eg hair colour)

Question 17

Justify why xxx is a recessive condition - 3 marks

Answer 17

• 2 recessive alleles are needed to have X condition
• individuals A and B do not have X but some of their children do
• therefore A and B must be heterozygous

Question 18

What is the definition of a gene pool

Answer 18

total number of genes of every individual in a population

Question 19

what are allele frequencies?

Answer 19

proportion of each allele within a gene pool

Question 20

what are 2 types of selection?

Answer 20

• stabilising
• disruptive
  (- directional)

Question 21

what is transient polymorphism?

Answer 21

selective advantages changes overtime (disruptive selection)

Question 22

3 factors that can influence allele frequencies in a population:

Answer 22

• founder effect
• genetic bottlenecks
• genetic drift

Question 23

what is a genetic drift?

Answer 23

changes in gene pool bcs of random selection of alleles

Question 24

what is the founder effect?

Answer 24

when small groups of individuals leave a larger pop and develop new isolated pop
- alleles in offspring are determined by the founders

Question 25

what are population bottlenecks?

Answer 25

when entire species are wiped out except for a small group of survivors so numbers and diversity fall dramatically

Question 26

what is the hardy weinberg equation and what do they stand for?

Answer 26

p^2 + 2pq + q^2 = 1 p^2 = homozygous dominant q^2 = homozygous recessive 2pq = heterozygous p + q = 1 p= dominant ALLELE q= recessive ALLELE

Question 27

in chi squared hypothesis testing, when do we accept or reject H0?

Answer 27

when calculated chi2 value > value on table (n-1, 0.05), reject H0.

Question 28

How does inbreeding cause genetic defects? (2 marks)

Answer 28

Reduced gene pool Increasing chance of homologous recessive genotypes for genetic defects

Question 29

What is a gene locus? 2 marks

Answer 29

Where the allele is located on a chromosome

Question 30

What are conditions for the Hardy-Weinberg equation?

Answer 30

- no mutations - random mating - large population - no selection pressures

Question 31

Do alleles mutate due to selection pressure?

Answer 31

NO!!! They mutate randomly Not 'due to' selection pressure

Question 32

Explain HOW breeding programs in zoos can maximise genetic variation in populations before reintroduction to their natural habitat. (2 marks)

Answer 32

- stud book to log mating between individuals - so prevents closely related individuals mating - exchange alleles between zoos

Question 33

Explain why a person who is heterozygous does not show the symptom of XYZ (that is recessive). (2 marks)

Answer 33

- heterozygotes have one dominant copy of the allele, so it’s expressed - so protein can still be made

Question 34

Compare and contrast stabilising selection with disruptive selection. (3 marks)

Answer 34

- both change the frequency of alleles / change genetic diversity - both select against less advantageous phenotypes - disruptive selects against median phenotypes, stabilising selects against extreme phenotypes - disruptive leads to 2 distinct population, stabilising maintains one

Question 35

Why offspring of genetic bottleneck population have higher chance of health problems?

Answer 35

- reduced genetic diversity and gene pool - chances of inheriting two harmful recessive alleles increases