Dragon Genetics -- Independent Assortment and Genetic Linkage This activity, by Dr. Ingrid Waldron and Jennifer Doherty, Department of Biology, University of Pennsylvania, © 2008, incorporates ideas from Dragon Genetics Lab, 2002, Bob Farber, Central High School, Philadelphia, PA and Dragon Genetics by Dr. Pamela Esprivalo Harrell, in the January 1997 issue of Science Scope, 20:4, 33-37. 1 In this activity you will study the patterns of inheritance of multiple genes in (imaginary) dragons. These dragons have two pairs of homologous chromosomes in each cell. You will see that, since genes are carried on chromosomes, the patterns of inheritance are determined by the behavior of chromosomes during meiosis and fertilization. The Law of Independent Assortment -- Inheritance of Genes on Different Chromosomes For this activity, we will only consider one gene on each chromosome. These genes are described in the following table. Dominant Alleles Recessive Alleles Chromosome 1 W = has wings w = no wings Chromosome 2 H = big horns h = small horns The mother dragon is heterozygous for the wing gene ( Ww ) and the horn gene ( Hh ). The father is homozygous recessive for the wing gene ( ww ) and the horn gene ( hh ). What phenotypic traits will each parent have? (Phenotypic traits are the observable bodily characteristics.) Draw the appropriate characteristics for each parent. Mother Father Has wings, big horns no wings, small horns Review of Inheritance of Single Genes Draw a Punnett Square to show the inheritance of the horn alleles for a mating between this mother and father. H h h Hh hh h Hh hh 1 1
On average, what fraction of the baby dragons will have big horns? 50% Predictions of Inheritance of Two Genes on Different Chromosomes To predict the inheritance of the wing and horn genes, you first need to determine the genotypes of the eggs produced by the heterozygous ( WwHh ) mother dragon and the sperm produced by the homozygous ( wwhh ) father dragon. Considering both the wing and horn genes, what different genotypes of eggs could the heterozygous mother dragon produce? Use the figure below to answer this question. WWHH, wwhh, WWhh, wwHH Notice that, in a cell that is prepared for meiosis 1, the homologous chromosomes are always paired with each other, but the specific arrangement of the chromosomes can differ. Describe this difference and the effect that this has on the genotypes of the eggs produced. It affects what phenotypes will be presented with the other. What genotypes or genotype of sperm can the homozygous ( wwhh ) father dragon produce? Draw a diagram to show how meiosis would occur in the father, starting with a diploid cell ready to undergo meiosis 1 and ending with four haploid sperm. Look on paper turned in. Two equally probable chromoso me arrangem ents in Meiosis I: or Meiosis II: or Gametes or with Genotype s: or 2
The next step in predicting the inheritance of the wing and horn genes is to predict the outcome of fertilization between these eggs and sperm. In the following chart, label the
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