exam questions Flashcards
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)
- females can be heterozygous
- females have 2 alleles
- males only have 1
explain why most of the offspring look like the parents (3)
- autosomal linkage
- crossing over results in recombinants
- offspring with phenotypes same as parent are more likely
what does it mean if genes for body colour and wing length are linked? (1)
genes/loci are on same chromosome
if genes are not linked what ratio of phenotypes would be expected? (1)
1:1:1:1
why would a chi square test be used? (2)
- nominal data
- test of difference
give a piece of evidence that suggests an allele is dominant (1)
2 parents with this trait can produce offspring with other trait
- so parents must be heterozygous
give a piece of evidence that suggests an allele is not sex linked (1)
father would pass X chromosome to daughter
what is meant by a sex linked gene (1)
gene is on X or Y chromosome
describe crossing over (1)
bivalents exchange genetic information
describe anaphase (2)
homologous chromosomes pulled apart at centromere by spindle fibres
what factor is necessary to ensure that the effect of chance variations in gene frequencies are minimised (1)
large gene pool
what events are involved in the formation of a new species? (3)
- gene mutation
- selection pressure
- change in environment
describe how genetic variation is achieved during meiosis (4)
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
what type of variation is controlled by few genes and unaffected by the environment? (1)
discontinuous
what type of variation is controlled by only genetic factors? (1)
continuous
why do scientists predict that bananas will become extinct within a few years? (3)
- no sexual reproduction
- little genetic variation
- susceptible to disease
how may a phenotypic ratio differ if genes are autosomally linked? (1)
higher proportion of heterozygous offspring
why may observed results not match expected? (1)
random fertilisation
on an inheritance pattern flow chart, what would suggest that an allele is sex linked?
if only males inherit the trait
on an inheritance pattern flow chart, what would suggest that an allele is recessive?
healthy parents produce offspring with the trait
describe how one allele might inhibit the expression of another (2)
- the allele produces an enzyme
- the product of this inhibits the enzyme encoded by the other allele
on an inheritance pattern flow chart, what would suggest that a sex linked allele is dominant?
daughters inherit it from affected fathers
outline how a fossa could have evolved from a mongoose (4)
- allopatric speciation
- random mutations
- different selection pressures on each population as they adapt to different environments
- advantageous alleles passed on
- example of directional selection
what conditions must be present in order for speciation to occur? (3)
- large gene pool
- natural selection
- time
state 2 reasons why it may be inappropriate to use the hardy weinberg principle (2)
- small sample
- mutations
describe how DNA can be used to provide evidence to support theory of evolution (2)
- compare DNA base sequences
- similar base sequence = recent common ancestor
what type of isolation is different diets?
behavioural
