Cell division & inheritance gcse qs
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Cell division & inheritance gcse qs Presentation Transcript

  • 1. Cell division & inheritance GCSE Questions
  • 2. genes gametes
  • 3. XX Y XY XX
  • 4. 50% or ½
  • 5. XX Female XY Male XY XX Male Female
  • 6. Meiosis 23 23 any two from (introduces) variation prevents the risk of all being the same and a disease wiping out population or prevent monoculture two parents to raise offspring
  • 7. both parents carry a recessive allele or gene or are heterozygous
  • 8. any two from: • other scientists not aware of his work • chromosomes / DNA / genes not seen / discovered / known do not accept there was no interest in genetics • other theories accepted at the time • not considered to be a scientist / not eminent / respected allow ‘he was just / only a monk’
  • 9. random selection 19:21 or about 1:1
  • 10. (genotype / gametes from P / father) D and d (*) 1 (genotype / gametes from Q / mother) d and d / accept d(*) 1 offspring genotypes correctly derived from correct gametes(*) 1 offspring phenotypes R and S identified 1 (*) eg may be in punnett square allow own upper and lower case symbols or allow any symbol correctly used with key
  • 11. For cystic fibrosis pros: • termination of pregnancies would reduce number of people with cystic fibrosis (in population) • reduce health-care costs • allows decision / emotional argument, eg allows people to make choices about termination cons: • possible damage / risk to embryo / fetus / baby • possible harm / risk to mother • (may) have to make ethical / moral / religious decisions For polydactyly: • detects possibility of ‘disfigurement’ in embryo • but condition not life threatening • so risks to fetus / mother unjustified
  • 12. Aa or aA allele / gene for vestigial wings / a is recessive or vestigial is recessive or A is dominant or A would override the effect of a or A present gives long wings
  • 13. (b) parental genotypes correct – both Aa NB can pick up chain of logic at any point correctly derived from candidate’s previous point 1 gametes correctly derived from P genotypes 1 offspring genotypes correctly derived from gametes 1 3:1 ratio recognised wrong cross and not 3:1 ratio = max 2
  • 14. eggs produced by meiosis therefore contain only half of mother’s DNA
  • 15. B (child has) mother’s 25 / 28 / 30 / 31 or child gets 17 / 19 / 22 / 24 from mother 1 (child has) man B’s 10 / 12 / 13 / 14 or child gets 18 / 20 / 21 / 23 from B no bars / DNA / lines from man A correspond to child 1 1
  • 16. twins have come from one (fertilised) egg Y sperm / Y chromosome produces boys D
  • 17. any two from: • (formed from) different egg / 2 eggs • (formed from) different sperm / 2 sperm • have different genes / alleles / chromosomes / DNA
  • 18. (medical) research / named eg growing organs or medical / patient treatment allow (embryo) cloning do not allow designer babies / more babies any one from: • ethical / moral / religious objections ignore cruel / not natural / playing God • potential harm to embryo allow deformed ignore harm to mother
  • 19. gametes i.e. B b and B b 1 correct combination of genotypes i.e. BB, Bb, Bb, bb 1 correct analysis of phenotypes i.e. 3 black fur 1 with brown fur award one mark for the recognition that it is down to chance (which two gametes fuse) and not simply ‘because it’s a prediction’ do not accept mutation
  • 20. (b) (i) B is dominant/ an allele is dominant if it is expressed in the heterozygous phenotype candidates are likely to use a variety of ways of expressing their ideas 1 b is recessive/ a recessive allele is not expressed in the presence of its contrasting allele do not accept powerful do not accept stronger 1 (ii) alleles are different forms of a gene controlling a characteristic and occupying the same site on homologous chromosomes (e.g. B or b) 1 genes are the units of DNA/sites on chromosomes carrying the information that determines characteristics (e.g. bB) 1
  • 21. white