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Answers to genetics test. One . Duroc – bbww Hampshire – BBWW F1 - BbWw. One . b) For achieved  Pure breeding means that the individual has a homozygous genotype / can produce only one type of allele.

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Duroc – bbww

Hampshire – BBWW

F1 - BbWw


b) For achieved  Pure breeding means that the individual has a homozygous genotype / can produce only one type of allele.

For Merit  Homozygous parent can pass on only one type of allele (for that trait) to its offspring (there is NO variation in the alleles) so offspring have same alleles and phenotype as the parent.


c) Someone draw on the board

(Gametes correct for A, whole punnet correct for M)


d) For achieved  One of bbWWor bbWw

For Merit  Both (above) and no other genotype given.


e) For achieved  3/16 or 3:15 or correct decimal or correct %


f) For achieved  Gives genotypes as bbWW and describes breeding suspect pigs with recessive genotype (bbww) pigs and check whether offspring have white bands or are solid red only.

For M  As for A, and also:

  • Solid red offspring indicates suspect pig is bbWw, all white banded offspring indicates suspect pig (may be) bbWW.

f) cont…

For E  Need M + explanation of the need for several breedings. Eg. If no solid red (bbww) pigs occur in the large numbers of offspring, then the suspect pig is (almost certainly) bbWW so pure breeding.

Answer must be supported with correct punnet squares (bbWw x bbww) and (bbWW x bbww)

  • Describes two of: (For achieved)
  • Mutations in DNA creates new alleles.
  • Independent assortment of homologous chromosomes produces genetically varied gametes.
  • Crossing over and recombination between non sister chromatids in meiosis produces new allele combo’s in gametes.

b) For A  Mutation must occur in gamete producing cells for it to enter the gene pool.

For M  If the gamete with the mutation is fertilised and the offspring produced is viable, then the mutation will enter the gene pool of the population.


c) For A  Describes natural selection as causing:

  • Mutations that are helpful/favourable to become established in the gene pool

For M Explains one of:

  • Selection pressures will cause individuals with favourable allels to survive and reproduce so establishing and increasing the frequency of these alleles in the gene pool
  • Selection pressures will cause individuals with unfavourable alleles to not survive/ have reduced chance of survival, so these alleles will not get established in the gene pool.
  • For A  Any 3 of:
  • Bottleneck effect – eg numbers of robins were greatly reduced so likely loss / reduction in allele frequency with likely reduction in genetic diversity.
  • Founder effect – eg only 6 breeding pairs intro’d to Ulva so alleles present in their gene pool not likely to be representative of the mainland.
  • Genetic drift – loss /reduction in specific alleles due to chance which is likely to be more pronounced in the small robin pop’ so corresponding loss of genetic diversity.
  • For A cont
  • Mutation – changes to genetic code creating new alleles. If occuring in gamete producing cells, will enter gene pool as inherited.
  • Natural selection – changes in the environment cause change in selection pressures on robins so favourable alleles will be selected for and increase in frequency in gene pool.

b) For A  Describes inbreeding:

  • Eg the breeding of closely related individuals in the robin pop.
  • AND it’s effect on one evolutionary process
  • Inbreeding in the small robin pop’ is likely to further reduce the genetic diversity of the population that has occurred in bottleneck effect/founder effect/genetic drift.
  • Mutations that are favourable will become established / increase in frequency in the gene pool more rapidly with inbreeding.

b) For M  Explains inbreeding:

  • The small size of the pop increases the occurrence of inbreeding occurring by chance so that the degree of relatedness between all members of the population is high. This increases the chances of harmful recessive alleles coming together in any individual so reducing its fitness.
  • AND explains its effects on one evolutionary process

b) Cont…

  • Inbreeding will reduce the genetic diversity of the small pop that has already occurred in bottleneck/founder/genetic drift as the breeding of closely related individuals increases the chances of the loss of alleles from the gene pool.
  • Closely related individuals have alleles in common. A mutation that creates a new allele will be more common in related individuals. Inbreeding will therefore increase the chances of a mutation spreading through the pop’ and so becoming established/increasing in frequency in small gene pool.