Question

Nameindulia Los Drosophila Genetics Predictions-L113 (20 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. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIII 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 8888 Chromosome Pair #1 (sex chromosomes) Chromosome Pair #2 Chromosome Pair #3 Chromosome Pair #4 (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 Drosophila flies is similar to that in humans in that: XX = female, XY = male. The chromosomes of a male would look like the following: Chromosome #1 +Y chromosome (smaller! Chromosome Pair #2 Chromosome Pair #3 Chromosome Pair #4 (autosomes) (autosomes) (autosomes)

Answer 1

ANSWER 1.A :-

1. First of all, the characters of fire breathing and laser projection are encoded by the autosome or the non-sex chromosomes. The germ cells are the ones which undergo the process of meiosis in order to produce the gametes and in this case the egg cells.
2. So, the autosomal characters won't be segregated as a part of meiotic division but is restricted to mitotic division.
3. So, the entire individual is able to produce all the cells which may be able to display the desired traits encoded by the autosomal genes. The eggs that will be produced will be having all X-chromosomes although there will be production of polar bodies thereby restricting the chromosome to only a single egg cell as the polar bodies are reutilized by the organism. Still, the representation of segregation of chromosome into gametes is as follow :-

ANSWER 1.B :-

The genotype of this gamete will be (3 + X) in which three represents the number of autosome and X indicates the sex chromosome. (b/d) should be the correct representation for the autosomes.

ANSWER 2.A :-

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1. Taking into consideration, the male drosophila will get segregated forming 4 sperm cells and will show presence of either X-chromosome or Y-chromosome along with the dominant form of the alleles according to the condition mentioned in the question.

ANSWER 2.B :-

The genotype of the male drosophila should be (3 + X/Y) in which three represents the number of autosomes and X/Y indicates the sex chromosomes. (D/B) should be the genotype for the autosomes in consideration.

ANSWER 3.A :-

The autosomal genotype which is considered here should be (Dd/Bb) which indicates that the combination will be heterozygous. This will be the condition for both the males and the females.

ANSWER 3.B :-

The offsprings would not be having the mutated form of the genes in homozygous recessive condition and hence the normal wild-type phenotype will be seen.

ANSWER 3.C :-

If the offsprings are self-crossed, a Mendelian ratio of 9:3:3:1 for the autosomal genes will be obtained. There will be 9 wild type individuals, 3 will show mutated gene for fire breathing and wild type/unmutated laser shooting gene, 3 will be show wild type/unmutated fire breathing gene and mutated laser shooting gene and 1 will show both the mutated forms.

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