exam questions

Question 1

in fruit flies, a gene for eye colour is carried on the X chromosome. the allele for red eyes (R) is dominant to the allele for white eyes (r). why are male fruit flies more likely to have white eyes than females? (2)

Answer 1

• females can be heterozygous
• females have 2 alleles
• males only have 1

Question 2

explain why most of the offspring look like the parents (3)

Answer 2

• autosomal linkage
• crossing over results in recombinants
• offspring with phenotypes same as parent are more likely

Question 3

what does it mean if genes for body colour and wing length are linked? (1)

Answer 3

genes/loci are on same chromosome

Question 4

if genes are not linked what ratio of phenotypes would be expected? (1)

Answer 4

1:1:1:1

Question 5

why would a chi square test be used? (2)

Answer 5

• nominal data
• test of difference

Question 6

give a piece of evidence that suggests an allele is dominant (1)

Answer 6

2 parents with this trait can produce offspring with other trait
- so parents must be heterozygous

Question 7

give a piece of evidence that suggests an allele is not sex linked (1)

Answer 7

father would pass X chromosome to daughter

Question 8

what is meant by a sex linked gene (1)

Answer 8

gene is on X or Y chromosome

Question 9

describe crossing over (1)

Answer 9

bivalents exchange genetic information

Question 10

describe anaphase (2)

Answer 10

homologous chromosomes pulled apart at centromere by spindle fibres

Question 11

what factor is necessary to ensure that the effect of chance variations in gene frequencies are minimised (1)

Answer 11

large gene pool

Question 12

what events are involved in the formation of a new species? (3)

Answer 12

• gene mutation
• selection pressure
• change in environment

Question 13

describe how genetic variation is achieved during meiosis (4)

Answer 13

prophase 1 = crossing over of non sister chromatids
metaphase 1 = independent assortment of homologous chromosomes
metaphase 2 = independent assortment of chromatids
anaphase 2 = random segregation of chromatids

Question 14

what type of variation is controlled by few genes and unaffected by the environment? (1)

Answer 14

discontinuous

Question 15

what type of variation is controlled by only genetic factors? (1)

Answer 15

continuous

Question 16

why do scientists predict that bananas will become extinct within a few years? (3)

Answer 16

• no sexual reproduction
• little genetic variation
• susceptible to disease

Question 17

how may a phenotypic ratio differ if genes are autosomally linked? (1)

Answer 17

higher proportion of heterozygous offspring

Question 18

why may observed results not match expected? (1)

Answer 18

random fertilisation

Question 19

on an inheritance pattern flow chart, what would suggest that an allele is sex linked?

Answer 19

if only males inherit the trait

Question 20

on an inheritance pattern flow chart, what would suggest that an allele is recessive?

Answer 20

healthy parents produce offspring with the trait

Question 21

describe how one allele might inhibit the expression of another (2)

Answer 21

• the allele produces an enzyme
• the product of this inhibits the enzyme encoded by the other allele

Question 22

on an inheritance pattern flow chart, what would suggest that a sex linked allele is dominant?

Answer 22

daughters inherit it from affected fathers

Question 23

outline how a fossa could have evolved from a mongoose (4)

Answer 23

• allopatric speciation
• random mutations
• different selection pressures on each population as they adapt to different environments
• advantageous alleles passed on
• example of directional selection

Question 24

what conditions must be present in order for speciation to occur? (3)

Answer 24

• large gene pool
• natural selection
• time

Question 25

state 2 reasons why it may be inappropriate to use the hardy weinberg principle (2)

Answer 25

• small sample
• mutations

Question 26

describe how DNA can be used to provide evidence to support theory of evolution (2)

Answer 26

• compare DNA base sequences
• similar base sequence = recent common ancestor

Question 27

what type of isolation is different diets?

Answer 27

behavioural