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Download Assessment Schedule 2010 AS 90459 (Biology 2.3) Describe
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Assessment Schedule 2010 AS 90459 (Biology 2.3) Describe Genetic variation and change Question ONE (a) Achievement Merit Sufficiency: Describes any As for Achieved and four of (a), (b), (c), (d), (e), explains two of (b), (c), (f). (d), (f). Duroc : bbww Hampshire : BBWW F1 : BbWw (b) Pure breeding means that the individual has a homozygous geneotype / can produce only one type of allele (c) 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 parent. BW Bw bW bw BW BBWW BBWw BbWW BbWw Bw BBWw BBww BbWw Bbww bW BbWW BbWw bbWW bbWw bw BbWw Bbww bbWw bbww Gametes correct (A):whole Punett Square correct (M) (d) One of bbWW; bbWw (e) 3/16 or 3 : 15 or correct decimal or correct %. Both bbWW and bbWw and no other genotype given. Excellence Discusses (f); explains (b) and (c); describes (a) and (e). (f) TWO (a) Gives genotype as bbWW and describes breeding suspect pigs with recessive genotype (bbww) pigs and check whether offspring have white bands or are solid red only. Sufficiency: Describes mutation and one other source of variation in (a) and describes (b) and (c). Describes TWO of eg Mutation(s) 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 combinations in As for Achieved and explains that Solid red offspring indicates suspect pig is bbWw; all white banded offspring indicates suspect pig (may be) bbWW. if any offspring do not have white band / are solid red (bbww) then adult is heterozygous (bbWw) and not pure breeding for white banded offspring. As for Achieved and explains ONE of (b) of (c). As for Merit and includes 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 supported with correct Punnet Squares of crosses (bbWw x bbww and bbWW x bbww) to show the probability of getting white banded and solid red offspring. As for Merit and explains both (b) and (c) gametes. (b) Mutation must occur in gamete producing cells [not somatic cells] for it to enter gene pool. If the gamete with the mutation is fertilized and the offspring produced is viable, then the mutation will enter the gene pool of the population. (c) Describes Natural selection as causing : Explains ONE of ; mutations that are helpful / favourable to become established in the gene pool mutations that are helpful / unfavourable to not become established in the gene pool Selection pressures will cause individuals with favourable alleles to survive and reproduce (increased fitness) 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 surviving (reduced fitness) so these alleles will not get established in the gene pool or be present in low frequencies in the gene pool Discussion explains the role of NS in determining the presence of both favourable and unfavourable alleles in the gene pool linked into a comprehensive answer. THREE (a) Sufficiency : Describes three evolutionary processes in (a) and describe inbreeding and its effect on one of these evolutionary process in (b). Any three of : Bottleneck effect – eg numbers of robins were greatly reduced so likely loss / reduction in allele frequency with likele reduction in genetic diversity. Founder effect – eg only 6 breeding pairs introduced to Ulva so alleles present in their gene pool not liely to be representative of the mainland / ancestral population so likely reduced gentic diversity. Genetic drift – loss / reduction in specific alleles due to chance which is likely to be more pronounced in the small robin population so corresponding [increased] loss of genetic diversity. As for Achieved and explains inbreeding and its effect on one evolutionary process. As for Merit and explains the effect of inbreeding on three evolutionary processes linked to the decrease of diversity in the gene pool and the rapid increase in frequency of favourable alleles in the gene pool of the robins on Ulva island. (b) Mutation – changes to genetic code creating new alleles. If occurring 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. Describes inbreeding eg Explains inbreeding eg the breeding of closely related individuals eg siblings, children to parents; grand children to grandparents in the robin population. and its effect on one evolutionary process eg Inbreeding in the small robin population is likely to further reduce the genetic diversity of the population that has occurred in bottleneck effect / founder effect / genetic drift The small size of the population 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 effect on one evolutionary process eg Mutations that are favourable will become established / increase in Inbreeding will reduce the genetic Explains inbreeding and its effect on three evolutionary processes linked to the decrease of diversity in the gene pool and the rapid increase in frequency of favourable alleles in the gene pool. frequency in the gene pool more rapidly with inbreeding. diversity of the small population that has already occurred in bottleneck effect / founder effect / genetic drift as the breeding of closely related individuals increases the chances of the loss of alleles from the gene pool. Favourable alleles selected for in NS will increase in frequency more rapidly with inbreeding. 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 population and so becoming established / increasing in frequency in small gene pool. Favourable alleles are selected for so increases in frequency in the gene pool. Inbreeding will increase the spread of these favourable alleles through the small gene pool so further increasing their frequency. Judgement Statement Achievement Two questions answered correctly. Minimum of 2 x A. Achievement with Merit Achievement with Excellence All questions answered correctly including TWO at Merit level. All questions answered correctly including TWO at Excellence level. Minimum 2 x M + 1 x A Minimum 2 x E + 1 x A