Genetics Flashcards
what is the null hypothesis always for chi-squared?
there is no significant difference between observed and expected results
when the chi-squared test is carried out, what is it carried out to compare?
how well observed and expected match results
to find out if there is a significant difference between your observed and expected results, what do you need to compare your chi-squared value to?
critical value
what is the critical value?
value of chi squared that corresponds to 0.05 probability level that the difference between observed and expected results is DUE TO CHANCE
if chi squared value is larger than / equal to critical value then…
- is significant difference
- between observed and expected
- null rejected
if chi-squared value smaller than critical value then…
- no sig difference
- between observed and expected
- null NOT rejected
male cats with tortoiseshell phenotypes dont occur.
why?
- Y chromsome doesnt carry allele
- cannot be hetero
the allele for polydactyly is dominant.
some cat breeders select for polydactyly.
describe how this would affect the frequences of the homozygous genotypes for this gene in their breeding populations over time?
- homo dominant inc
- homo recessive dec
in birds, males are XX and females are XY.
use this info to explain why recessive, sex linked characteristics are more common in female birds than male birds?
- females have one allele
- recessive allele always expressed
explain the advantage of presenting results as a ratio?
- able compare (valid)
- number / sample size may vary
gene/loci on same chromosome
how many antigen determining alleles will be present in a white blood cells?
give a reason for your answer?
- 2
- white blood cells = diploid
explain 2 reasons why the fruit fly is a useful organism for studying genetic crosses?
- large number of eggs - reduces sampling error
- simple nutrient medium - reduces cost
suggest why observed ratios are often not the same as expected ratios?
- fertilisation is random
- population sample small
male fruit flies are more likely than female fruit flies to show a phenotype produced by a recessive allele carried on the X chromosome.
explain why?
- males have one allele - only need 1 recessive allele
- females ned 2 recessive alleles
in an investigation, the numbers for tongue rolling and thumb characteristics do not add up to 200.
for each characteristic suggest one reason why the numbers do not add up to 200?
- tongue rolling - some people not willing to tell
- thumb - thumb bending subjective
- 4 and 3
- both 4 and 3 are carries / hetero
explain one piece of evidence from the diagram which proves that the allele for Tay-Sachs disease is not on the X chromosome?
- 11 affected, 3 not
- 3 doesnt have recessive allele on his chromsome
suggest why the actual percentage of heterozygotes is likely to be lower in future generations than the answer you would have calc?
affected individuals usually dont reproduce
suggest advantages of using island populations?
- can record all individuals on small islands
- less sampling error
- diff rates of mutation
- inbreeding more likely
- little gene flow
the geneticist concluded that arm-folding is NOT determined by a single gene with a dominant allele and a recessive allele.
use info from figure 2 to explain why she reached this conclusion?
- if R recessive, R x R parents cant produce L offpsring
- if L recessive, L x L parents cant produce R offspring
- R x R and L x L parents produce both types of offspring
both twins folded arms differently
- 1,2 and 5
- 1 must pass on recessive allele to 5
explain why scientists used the same restriction endonuclease enzyme on each DNA sample?
- cut DNA at same base sequence
- so get fragments with required gene
explain why cells in mitosis were used?
- chromosomes visible
- can see which chromosome DNA probe attaches to
- 2 is not colour blind and 4 is colour blind
- so 2 must be hetero
gene/loci on same chromsome
use your knowledge of gene linkage to explain these results?
- GgNn individuals produce mainly GN and gn gametes
- crossing over produces some Gn and gN gametes
- fewer Ggnn and ggNn individuals
- GN linked with gn
explain why the number of people showing LP would rapidly increase once selection for this condition had been established?
- domiant allele
- always expressed in phenotype
lactase persistence is caused by a mutation in DNA.
this mutation doesnt occur in the gene coding for lactase.
suggest and explain how this mutation causes LP?
- mutation in promoter gene for TF
- lactase gene continues to be transcribed
explain evidence that allele for white fur is recessive
parents are hetero
evidence from a diagram that muscular dystrophy is
sex linked
only seen in males
evidence that Li-Fraumeni syndrome caused by
dominant allele
C doesnt have condition = carrier
evidence that Li-Fraumeni syndrome
not sex linked
- father (A) would pass on X chromosome to daughter
- shes not affected
the families history of cancer was investigated when a person asked for genetic counselling.
at the time she was 25 years old
what advice could a genetic counsellor give about her prbability of developing cancer?
- dont know if cancer will develop
- dont know if father hetero
Li-Fraumeni syndrome is caused by a mutation affecting a tumour suppresor gene called TP53.
the gene codes for protein that initiated death of cells where damaged DNA cannot be repaired.
mutated TP53 gene leads to production of non-functional protein
suggest how non-functional protein may lead to cancer
- mutation changes DNA of cell
- damaged DNA not repaired
- mutation leads to loss of control of cell division
- cells carried to other parts of body
