Transcript
Pre-Lab Questions You are observing a species of mice in which brown fur color is dominant to white fur color. When a brown mouse is crossed with a white mouse, all of their offspring have brown fur. Why did none of the offspring have white fur? The brown parent was homozygous dominant. The white parent was homozygous recessive. To express white fur you need a white allele from each parent. Can a person’s genotype be determined by their phenotype? Why or why not? No, a person's genotype cannot be determined solely by their phenotype as many genes in our genome do not get expressed. Are incomplete dominant and co-dominant patterns of inheritance found in human traits? If yes, give examples of each. Yes, codominance – ABO blood system. Incomplete dominance is observed in traits that occur on just one gene. In humans, however, traits are from multiple genes, and it is rare. An example is the disease familiar hypercholesterolemia. Consider the following genotype: Yy Ss Hh. How many different gamete combinations can be produced? 8 Many traits (phenotypes), like eye color, are controlled by multiple genes. If eye color were controlled by the number of genes indicated below, how many possible genotype combinations would there be in the following scenarios? 5 Eye Color Genes: 55 10 Eye Color Genes: 210 20 Eye Color Genes: 820 Experiment 1: Punnett Square Crosses Part 1: Post-Lab Questions Set up and complete Punnett squares for these crosses (remember Y = yellow, y = blue): YY and Yy YY and yy Answer these questions: What are the resulting phenotypes? 100% yellow Are there any blue kernels? No How can you tell whether or not there are blue kernels? All kernels are yellow because they yellow allele (Y) is dominant over blue allele (y) Set up and complete a Punnett square for a cross of two of the F1 from Step 1 (above). Answer these questions: What are the genotypes of the F2 generation? YY – 25% Yy – 50% yy – 25% What are their phenotypes? Yellow – 75% blue – 25% Are there more or fewer blue kernels than in the F1 generation? More Identify the four possible gametes produced by the following individuals (Y = yellow, y = blue, S = smooth, s = wrinkled): YY Ss: YS, Ys, YS, Ys Yy Ss: YS, yS, Ys, ys Create a Punnett square using these gametes as P1 and determine the genotypes of the F1. What are the phenotypes? What is the ratio of those phenotypes? Part 2: Data Tables Table 1: Parent Genotypes: Monohybrid Crosses Generation Genotype of Individual #1 Genotype of Individual #2 P Yy Yy P1 yY YY P2 yy Yy P3 Yy yy P4 YY yy Table 2: Generation Data Produced by Monohybrid Crosses Generation Possible Offspring Genotypes Possible Offspring Phenotypes Genotype Ratio Phenotype Ratio P YY, Yy, yy Yellow/blue 1:2:1 3:1 P1 Yy, YY yellow 1:1 1:1 P2 Yy,yy Yellow/blue 1:1 1:1 P3 Yy, yy Yellow/blue 1:1 1:1 P4 Yy, yy Yellow/blue 3:1 3:1 Part 2: Post-Lab Questions How much genotypic variation do you find in the randomly picked parents of your crosses? 4 How much in the offspring? 4 Pool all of the offspring from your five replicates. How much phenotypic variation do you find? 4 Is the ratio of observed phenotypes the same as the ratio of predicted phenotypes? Why or why not? What is the difference between genes and alleles? Genes are a long chain of nucleotide sequence which encode for a specific gene product whereas the allele is the alternative form of a gene that codes for the same function or protein which genes do. How might protein synthesis execute differently if a mutation occurs? Organisms heterozygous for a recessive trait are often called carriers of that trait. What does that mean? The individual does not express the condition but can pass it on to future generations. In peas, green pods (G) are dominant over yellow pods. If a homozygous dominant plant is crossed with a homozygous recessive plant, what will be the phenotype of the F1 generation? If two plants from the F1 generation are crossed, what will the phenotype of their offspring be? Green ; ¾ green and ¼ yellow Part 3: Data Tables Table 3: Parent Genotypes: Dihybrid Crosses Generation Genotype of Individual #1 Genotype of Individual #2 P yySS yyss P1 yySS yyss P2 YySs yySs P3 YySs YYss P4 yySs YYSS Table 4: Generation Data Produced by Dihybrid Crosses Generation Possible Offspring Genotypes Possible Offspring Phenotypes Genotype Ratio Phenotype Ratio P yySs Blue/smooth 16:0 16:0 P1 yySs Blue/smooth 16:0 16:0 P2 Yyss, YySS, YySs, yySS, yySs, yyss Yellow/wrinkled, yellow/smooth, blue/smooth, blue/wrinkled 1:1:2:1:2:1 1:3:3:1 P3 YySs, Yyss, YYSs, YYss Yellow/smooth, yellow/wrinkled 1:1:1:1 1:1 P4 YySS, YySs Yellow/smooth 1:1 16:0 Part 3: Post-Lab Questions How similar are the observed phenotypes in each replicate? All the replicates are similar with regards to their primary phenotype. How similar are they if you pool your data from each of the five replicates? Pooling the data will retain some similarities, while some differences will become obvious too. Is it closer or further from your prediction? Closer Did the results from the monohybrid or dihybrid cross most closely match your predicted ratio of phenotypes? The results from both crosses match the results predicted from ratios given by a theoretical cross. Based on these results, what would you expect if you were looking at a cross of 5, 10, or 20 independently sorted genes? The result obtained would vary from the experimental results due to the process of genetic selection. Over many generations, the recessive alleles will take place of the dominant alleles. Why is it so expensive to produce a hybrid plant seed? The experiment needs to be repeated several times before the desired characteristics are obtained. In certain bacteria, an oval shape (O) is dominant over round (o) and thick cell walls (T) are dominant over thin (t). Show a cross between a heterozygous oval, thick cell walled bacteria with a round, thin cell walled bacteria. What are the phenotypes of the F1 and F2 offspring? The range of F1 phenotypes would be oval and thick, oval and thin, round and thick, round and thin. F2 phenotypes: oval and thick, oval and thin, round and thick, round and thin.
