Drosophila Genetics predictions exercise-L113 (25 pts.) Part I. Meiosis and Punnett Squares Remember, whenever you use...

  
 

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Drosophila Genetics predictions exercise-L113 (25 pts.) Part I. Meiosis and Punnett Squares Remember, whenever you use Punnett Squares to solve genetics problems, be sure you are completing each of the following steps: 1) Identify the genotypes of the parents. 2) For the specific traits of interest, figure out what kinds of haploid gametes each parent can make. In each gamete, there should be one allele for each trait of interest. If there is more than one trait, make sure all possible combinations of alleles are represented in the resulting gametes. 3) For a Punnett square, write the gamete genotypes across the top (sperm) and down the left side (eggs). 4) Fill in the Punnett square, making sure all the genotypes are complete and diploid for all traits. 5) Determine the genotypic ratios and phenotypic ratios among the offspring. Citrus flies, like Drosophila, have 4 different chromosomes (haploid gamete cells are n = 4, and diploid somatic cells are 2n = 8) that might be represented as follows: BB Chromosome Pair #1 Chromosome Pair #2 Chromsome Pair 13 Chromosome Pair 14 (sex chromosomes) (autosomes) (autosomes) (autosomes) Chromosomes #2-4 are autosomes, which are the non-sex chromosomes. Chromosome #1 is the sex chromosome. The above individual has 2 "X" chromosomes and is thus a female. Sex determination in citrus flies is similar to that in humans: XX = female, XY = male. The chromosomes of a male would look like the following: Chromosome Pair #1 Chromosome Pair #2 Chromsome Pair #3 Chromosome Pair 4 (sex chromosomes) (autosomes) (autosomes) (autosomes) 1. Wild-type citrus flies have orange-colored eyes. A homozygous recessive mutation on chromosome #2 (genotype: y/y) results in lemon-yellow eyes. Another homozygous recessive mutation on chromosome #3 (genotype: r/t) results in red eyes. If a fly has two copies of the "y" allele and two copies of the " allele (genotype: y/y; r/t), it will phenotypically have white eyes. The chromosomes of a female white-eyed citrus flies would look like the following: a. With respect to the genes for these two traits, what kind of eggs would this individual produce? Remember, the process of meiosis results in the production of gametes, which contain the haploid (or "n") number of chromosomes. That is, they contain half the number of chromosomes (one of each pair of homologs) that are present in every cell of the adult. Draw the four chromosomes of an egg cell (i.e., a gamete) produced by the above female. b. What is the genotype the gamete drawn above? 2. A male citrus fly with orange-colored eyes (i.e., that is wild-type) is homozygous at both the "y" and "r" loci. The chromosomes of this individual would therefore look like the following: y+ r+ a. Draw the four chromosomes present in a sperm cell produced by this fly. b. What is the genotype of the gamete drawn above? 3. Suppose the female and male fies referred to above (in #1 and H2) were to mate. a. What would be the genotype(s) of their F1 offspring? b. What would be the phenotype(s) of their F1 offspring? c. Draw the chromosomes present in the cells from a female F1 offspring from this cross. 4. Now, assume that a F1 male and a F1 female offspring produced by the cross in #3 above mate with each other. a. List the possible gamete genotypes that will be produced by both the F1 male and the F1 female? b. Fill in the Punnett square for the trait of interest (i.e., eye color) based on the different sperm produced by the male and the different eggs produced by the female. c. What eye color phenotypes will be produced among the offspring of this cross? And what will be the expected ratio of these phenotypes? Drosophila Genetics predictions exercise-L113 (25 pts.) Part I. Meiosis and Punnett Squares Remember, whenever you use Punnett Squares to solve genetics problems, be sure you are completing each of the following steps: 1) Identify the genotypes of the parents. 2) For the specific traits of interest, figure out what kinds of haploid gametes each parent can make. In each gamete, there should be one allele for each trait of interest. If there is more than one trait, make sure all possible combinations of alleles are represented in the resulting gametes. 3) For a Punnett square, write the gamete genotypes across the top (sperm) and down the left side (eggs). 4) Fill in the Punnett square, making sure all the genotypes are complete and diploid for all traits. 5) Determine the genotypic ratios and phenotypic ratios among the offspring. Citrus flies, like Drosophila, have 4 different chromosomes (haploid gamete cells are n = 4, and diploid somatic cells are 2n = 8) that might be represented as follows: BB Chromosome Pair #1 Chromosome Pair #2 Chromsome Pair 13 Chromosome Pair 14 (sex chromosomes) (autosomes) (autosomes) (autosomes) Chromosomes #2-4 are autosomes, which are the non-sex chromosomes. Chromosome #1 is the sex chromosome. The above individual has 2 "X" chromosomes and is thus a female. Sex determination in citrus flies is similar to that in humans: XX = female, XY = male. The chromosomes of a male would look like the following: Chromosome Pair #1 Chromosome Pair #2 Chromsome Pair #3 Chromosome Pair 4 (sex chromosomes) (autosomes) (autosomes) (autosomes) 1. Wild-type citrus flies have orange-colored eyes. A homozygous recessive mutation on chromosome #2 (genotype: y/y) results in lemon-yellow eyes. Another homozygous recessive mutation on chromosome #3 (genotype: r/t) results in red eyes. If a fly has two copies of the "y" allele and two copies of the " allele (genotype: y/y; r/t), it will phenotypically have white eyes. The chromosomes of a female white-eyed citrus flies would look like the following: a. With respect to the genes for these two traits, what kind of eggs would this individual produce? Remember, the process of meiosis results in the production of gametes, which contain the haploid (or "n") number of chromosomes. That is, they contain half the number of chromosomes (one of each pair of homologs) that are present in every cell of the adult. Draw the four chromosomes of an egg cell (i.e., a gamete) produced by the above female. b. What is the genotype the gamete drawn above? 2. A male citrus fly with orange-colored eyes (i.e., that is wild-type) is homozygous at both the "y" and "r" loci. The chromosomes of this individual would therefore look like the following: y+ r+ a. Draw the four chromosomes present in a sperm cell produced by this fly. b. What is the genotype of the gamete drawn above? 3. Suppose the female and male fies referred to above (in #1 and H2) were to mate. a. What would be the genotype(s) of their F1 offspring? b. What would be the phenotype(s) of their F1 offspring? c. Draw the chromosomes present in the cells from a female F1 offspring from this cross. 4. Now, assume that a F1 male and a F1 female offspring produced by the cross in #3 above mate with each other. a. List the possible gamete genotypes that will be produced by both the F1 male and the F1 female? b. Fill in the Punnett square for the trait of interest (i.e., eye color) based on the different sperm produced by the male and the different eggs produced by the female. c. What eye color phenotypes will be produced among the offspring of this cross? And what will be the expected ratio of these phenotypes?

Answer rating: 100% (QA)

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