genetics fruit fly summary report

8/13/2019 Genetics Fruit Fly Summary Report

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Kathleen Swanson

BIO210L Th 9-12

September 28, 2013

Summary Report: Fruit Fly Labs 1-3

Introduction:

The Drosophila melanogaster, or fruit fly, is a model organism through which we are able to study

inheritance patterns, and single gene traits. Given their short life cycles, short reproductive periods,

smaller number of chromosomes, 8, and large amount of offspring produced with each mating, it is

advantageous to use the Drosophila for studying inheritance patterns (Mennella Lecture 2-2013). Three

virtual labs using Drosophila melanogaster were conducted over a period of two consecutive weeks to

gain practice and insight in formulating predictions of inheritance patterns when crossing (mating) a

mutant fly in possession of a single a mutation on a single gene with true-breeding (homozygous) wild

type flies (normal). Crossing both the parent generations and the resulting F1 generations can yield a great

deal of information about the genotype in each as they demonstrate observable phenotypic expressions

that allow us to determine the inheritance patterns of the mutations being observed, which trait is

dominant or recessive, whether there are heterozygotic or homozygotic alleles involved, and ascertain

whether a mutant allele is contained on a sex or autosomal chromosome. Some of mutations observed

include: body color, eye color, wing size/absence. The following notations are used throughout the

discussion.

Methods:

All three virtual labs were conducted using the StarGenetics software. Wild type flies from the parent

generation were said to be pure-breeding (homozygotic). These wild type flies were mated with mutant

flies possessing a mutation in the following: eye color, wings, vestigial (no wings) body color.

Exercise 1:

A true-breeding male was crossed with a mutant, grounded female to determine if, and 1. The

mutant allele is dominant or recessive, and 2. If the mutant fly is heterozygotic or homozygotic for

this trait. The information from this cross was used to predict the phenotypic outcome of crossing


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the F1 offspring with each other. The predicted and experimental outcomes were compared;

sample sizes were increased to attempt to resolve the perceived conflict in phenotypic ratios and

new hypothesis drawn to account for the confirmed conflict.

Exercise 2:

A true-breeding female was crossed with a mutant, orange eyed male to determine if the mutant,

orange eyed male was heterozygous dominant or homozygous recessive. The F1 progeny are later

mated with each other and predictions of the F2 progeny made. Due to experimental results that

conflicted with predictions of the F2 progeny new predictions were made as to whether the orange

eye mutant trait was carried on an autosomal chromosome or sex linked. A true-breeding white

eyed female, with an allele recessive to wild type was crossed with the resulting F2, orange eyed

male to determine whether or not the white allele and orange eye allele were found on the same

genes or different genes and if the mutation that causes white eyes is on the sex chromosomes, or

the autosomal chromosomes.

Exercise 3:

A blue eyed white body female is mated with a male red eyed, grey bodied male to determine

dominant and recessive alleles for both traits and also to determine of each trait, if they are located

on an autosome or one the X chromosome. Phenotypic ratios of each trait, eye color and body

color are evaluated to determine if these traits are linked on the same chromosome.

Results:

Exercise 1:

In crossing a mutant female, with a wild type male generating 50 progeny, a near 1:1: ration was

observed; 56% wild type and 46% mutant. These results show that the mutant fly must have alleles that

are heterozygotic dominant; otherwise all of the progeny would have been wild type if the mutant parent

fly was homozygous recessive. We can also see from this crass that the wild type fly was homozygotic

recessive. In subsequent crosses an F1 female was crossed with an F1 male and a 2:1 ratio in favor of the

mutant type was observed, 66% to 34%. These results were contrary to predictions of a 3:1 ratio. So

sample sizes were increased to 1500 offspring and yet this 2:1 ratio remained 100% true to the initial

sample size of 50. It was concluded that the only remaining explanation, in conjunction with the dead

embryos found in the vials, was that the homozygous dominant mutant fly is unviable. To review, the


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mutant parent was determined to be (Gg), the wild type parent ( gg), the resulting offspring was 34% wild

type (gg) and 66% (Gg) mutant. Any genotype of (GG), dominant homozygous mutant was not viable.

Exercise 2:

In Laboratory exercise #2 an orange eyed mutant male, was mated with a true-breeding wild type female.

The resulting progeny were 100% phenotypically red eyed. This showed that the allele for the mutant

orange eye must be homozygotic recessive to the wild type allele. It was predicted that the crossing of the

F1 generation heterozygotic dominant wild type would result in a phenotypic ration of 3:1; however when

the mating was complete the result were quite different than predicted. Out of the 50 offspring, female

offspring had no orange eyes, and a total of male and females with red eyes were counted and represented

72% of the sample. The Male progeny demonstrated 28% orange eyed. This ratio is consistent with an X-

linked recessive orange mutant allele. Genotypically this crossed would reveal a 2:1:1: ratio (red eyedfemales:red eyed males:orange eyed males).

Additional crosses were done between one of the male, orange eyed mutant flies with a true-breeding

white eyed female whose allele is recessive to wild type red allele, in order to determine whether these

mutations in the white and orange eye are on the same or different genes. The predictive crosses made

showed that the white eyed female, and an orange eyed male, produced 50 offspring, all of which had red

eyes. This showed that the W allele and the sex linked R allele for red eyed since it was previously

established that the allele for red and orange eyes was located on the X-chromosome and the masking ofthe white eyed gene was complete with was clear that all off spring had to have possessed a heterozygotic

Ww, which is not consistent with sex linked traits which showed a 50% : 50% ratio upon performing a

monohybrid cross. To investigate whether this white eyed allele was located on an autosomal

chromosome or a sex chromosome a cross was performed between a red eyed male, xRyww and a white

eyed female, XrX

rWW. The results, had the W (white allele) been sex linked should adhere to a 50/50

ratio, however experimental results showed that the F1 progeny were all red and the F2 82% red and 18%

female.

Exercise 3:

In this exercise we had a blue eyed, white bodied female XeX

ebb parent and a red eyed gray bodied male

XEY

BB. Gray is autosomal dominant over white bodied, and eyes are sex linked with red eye alleles

dominant over blue eyes. Upon crossing these all gray bodied flies were obtained both male and female

but all female F1 progeny were red eyed and F1 males were all blue eyes. This demonstrated that the eye

color was sex linked and the body color allele was located on an autosomal chromosome, showing they


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couldnt exist on the same chromosome. Monohybrid crosses of both the eye color and body color reveal

that a 3:1 phenotypic ratio exists for body color; however the eye color results show red and blue as

seen in sex linked eye color ratios.

genetics fruit fly summary report

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