Genetics Exam Questions with correct Answers

Explain what causes the sperms of one kind to have 3% more DNA than sperms of the other kind. - Answer- some sperm have X chromosome; X is larger / has more genes than Y How do multiple alleles of a gene arise? - Answer- mutations; at different positions in the gene Explain why colour blindness is more common in men than in women. - Answer- males are XY and females XX / males have one X chromosome and females two X chromosomes; males only have one allele (of the gene) present therefore the recessive allele always expressed; colour blindness is masked in heterozygote / female needs 2 recessive alleles to be colour blind; Define phenotype - Answer- .(Expression/appearance/characteristic due to) genetic constitution/genotype/allele(s); The shape of the comb is controlled by two alleles of one gene. The allele for pea comb, A, is dominant to the allele for single comb, a. The colour of chicken eggs is controlled by two alleles of a different gene. The allele for blue eggs, B, is dominant to the allele for white eggs, b. The genes for comb shape and egg colour are situated on the same chromosome. A farmer crossed a male chicken with the genotype AaBb with a female chicken that had a single comb and produced white eggs. Explain how the farmer could know which of the female chickens produced through this cross would eventually produce blue eggs. - Answer- Those with pea combs would produce blue eggs because the dominant alleles for both characteristics will be inherited together from the same chromosome in the diploid sperm cell The shape of the comb is controlled by two alleles of one gene. The allele for pea comb, A, is dominant to the allele for single comb, a. The colour of chicken eggs is controlled by two alleles of a different gene. The allele for blue eggs, B, is dominant to the allele for white eggs, b. The genes for comb shape and egg colour are situated on the same chromosome. A farmer crossed a male chicken with the genotype AaBb with a female chicken that had a single comb and produced white eggs. Genes A and B are close together on the chromosome. This is important when trying to identify which of the female offspring would produce blue eggs. Explain why. - Answer- Reference to crossing over; Reduce chance of genes being separated (by crossing over); If crossing over occurred some gametes will contain alleles A and b, and so expressing the phenotype for one sex linked gene wouldn't be indicative of the organism also having the other allele Explain why a statistical test should be applied to the data obtained in genetic investigations - Answer- To determine the probability; [Accept: Likelihood] Of the results being due to chance; [Accept: Coincidence] The breeder had expected equal numbers of chocolate and cinnamon kittens from the cross between the chocolate male and black female. Explain why the actual numbers were different from those expected. - Answer- 1. Offspring ratios are a probability / not fixed / arise by chance / 2. gametes may not be produced in equal numbers / 3. fertilisation / fusion of gametes is random / 4. small sample; Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. - Answer- Homologous chromosomes pair up / bivalents form; 2. Crossing over / chiasmata form; 3. Produces new combination of alleles; 4. Chromosomes separate; 5. At random; 6. Produces varying combinations of chromosomes / genes / alleles (not twice) ; 7. Chromatids separated at meiosis II / later; Explain how meiosis results in this plant producing gametes with these genotypes. - Answer- Meiosis separates alleles / homologous chromosomes / pairs of chromosomes; Independent assortment / means either of A / a can go with either of L / l; Accept "random segregation" but cancel if reference to crossing-over What are sex-linked traits? - Answer- gene located on X / Y/ one sex chromosome; (allow gene on X or Y chromosome, not X and Y explain what is meant by dominant allele - Answer- is always expressed(in the phenotype) / produces (functional) proteins Suggest why the frequency of a s