Genetics Biology Worksheet ANSWERS

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QUESTION TWO: SEXUAL REPRODUCTION Meiosis is a particular form of cell division that produces male and female gametes. (a) Describe what gametes are and explain why they are needed for sexual reproduction. ANSWER TWO: SEXUAL REPRODUCTION (a) For Achievement you need TWO statements describing gametes. E.g. A gamete is a sex cell (e.g. an egg or sperm), A gamete has half the normal number of chromosomes as body cells. For Merit you need a correct explanation of the need for gametes: It is required in sexual reproduction to ensure that when a sperm fuses with an egg, the resulting first cell of the new organism has the correct number of chromosomes. Meiosis contributes to genetic variation. (b) Discuss how meiosis contributes to genetic variation, and why genetic variation is important in a population. In your answer, you should: describe what is meant by genetic variation explain how the process of meiosis leads to genetic variation explain why genetic variation is of benefit to a population You could draw labelled diagrams to support your answer. (b) For Achievement you need TWO statements describing genetic variation. E.g. Description of genetic variation: Genetic variation refers to a variety of different genotypes for a particular trait within a population. That the separation of alleles/ chromosomes during meiosis results in new combinations of alleles That variation aids survival when conditions change. For Merit you need a correct explanation of the need for gametes: E.g. meiosis produces genetic variation in a population by the separation of alleles which then allows new combinations of alleles to occur at fertilisation (this could include a labelled diagram of the meiosis process variations in a population might allow individuals to survive in changing conditions (and to pass on the ability to their offspring) For Excellence your answer needs to link the explanation of why genetic variation within a population is important for the survival of the species with the explanation of how inherited variation is constantly being generated by the process of meiosis, through the reshuffling of alleles. E.g. Meiosis produces gametes with half the number of chromosomes. This means that pairs of alleles are separated at meiosis. At fertilisation, which sperm fertilise which egg is due to chance and this results in new combinations of alleles. These new combinations of alleles cause variation The advantage of variation to a species is that it may enable some individuals to survive if some threatening event occurs. For example, if a new disease arrives, not all individuals will be wiped out.
QUESTION THREE: MONOHYBRID CROSSES The allele for a cleft chin (D) is dominant over the allele for a smooth chin (d). ANSWER THREE: MONOHYBRID CROSSES For Achievement you need THREE statements (from of a), b), and c) E.g. In (a) describes what a dominant allele OR relevant punnet square linked to pedigree diagram in (b), gives a reason for the presence of one of the alleles of the genotype in (c), completes the Punnett Square correctly D d D DD Dd The pedigree diagram below shows the chin types in a family. d Dd dd in (c), gives the correct probabilities for cleft chin and smooth chin. Probability of cleft chin = ¾ or 75% or 3 out of 4 Probability of smooth chin = ¼ or 25% or 1 out of four (a) (b) Explain how evidence in the pedigree diagram shows that the cleft chin allele (D) is dominant over the smooth chin allele (d). In your answer, you should: Describe what the term dominant allele means draw a Punnett square(s) to show your reasoning. Explain why the genotype of male A in generation 2 of the pedigree diagram must have the genotype Dd. For Merit you need TWO explanations in (a), explains the evidence that shows that cleft chin allele is dominant. E.g. A and B who both have a cleft chin produce a smooth chin child. If the cleft chin allele was recessive (d) they would not be able to produce a child with a smooth allele (as they would both have to be dd and would have no D allele to pass on), so the cleft chin allele must be dominant OR other correct evidence from chart. In (b), explains why individual A must have a dominant and a recessive allele using evidence from the pedigree diagram. E.g. As male A has a cleft chin this must mean that he carries at least one cleft chin allele (D). Male A and female B have a smooth chin boy, which means that A must have passed on a smooth chin allele (d) to the boy as to be smooth chinned the boy must have two recessive alleles, one from each parent. In (c), gives the correct probabilities based on the completed Punnet square parent alleles AND indicates that these can’t be used to predict what an individual will be. E.g. Probability of cleft chin = ¾ or 75% or 3 out of 4 Probability of smooth chin = ¼ or 25% or 1 out of four However these are only probabilities and cannot be used to predict the genotype of individuals
Page 1: QUESTION ONE: DNA AND VARIATION Gen
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Genetics Biology Worksheet ANSWERS

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