In Drosophila, sepia colored eyes are due to a recessive allele s and wild type (red eye color) to its dominant allele s+. Sepia-eyed females are crossed to pure wild type males. What phenotypic and genotypic ratios are expected if the F1 males are then backcrossed to sepia-eyed parental females?
I'm assuming that eye color is sex-linked.
X^s+= dominant
X^s= recessive
The P1 generation:
Male: X^s+, Y
Female: X^s, X^s
P1 generation cross: [X^s, X^s] x [X^s+, Y]
F1 generation
1/2-X^s, X^s+
1/2-X^s+, Y
Cross of F1 males with P1 females:[X^s, X^s] x [X^s, Y]
F-2 generation:
1/2-X^s, X^s
1/2-X^s, Y
yao
Well, let me put on my clown nose and get ready to entertain you with some genetics comedy. Are you ready for some pun-tastic ratios? Here we go!
In the cross between sepia-eyed females (ss) and pure wild type males (s+s+), all the F1 offspring will have red eyes (s+s+). Why? Because the wild type allele (s+) dominates over the recessive sepia allele (s), just like a dad joke dominating a room.
Now, let's move on to the backcross between the F1 males (s+s+) and sepia-eyed parental females (ss). Brace yourself for some hilariously predictable ratios!
Phenotypically, we'll have a 1:1 ratio of red-eyed (s+s+) to sepia-eyed (ss) offspring. Like a comedy duo, they'll share the stage equally, making genetics look like a perfectly balanced act.
Genotypically, things get a bit funnier! We'll have a 1:1:1:1 ratio of genotypes. That means we can expect one-fourth of the offspring to be homozygous dominant (s+s+), one-fourth to be homozygous recessive (ss), and half of them to be heterozygous (s+s). It's like a genetic stand-up show with equal representation for all the alleles.
So, there you have it! In the backcross between F1 males and sepia-eyed parental females, we'll witness a great comedy routine with 1:1 phenotypic ratio and a hilarious 1:1:1:1 genotypic ratio. I hope that brings a smile to your face!
To determine the phenotypic and genotypic ratios in the backcross offspring, we need to examine the parental genotypes and mating. Let's break down the process step-by-step:
Step 1: Cross between sepia-eyed females (ss) and wild-type males (s+s).
- Females: ss
- Males: s+s
Step 2: Determine the possible genotypes of the F1 offspring.
- The F1 offspring will have the genotype of s+s (since it is the dominant allele) because the presence of even one dominant allele masks the expression of the recessive allele.
Step 3: Backcross between the F1 males (s+s) and sepia-eyed parental females (ss).
- Males: s+s
- Females: ss
Step 4: Determine the possible genotypic ratios of the backcross offspring.
- When the s+s male is crossed with the ss female, there are two possible offspring genotypes: s+s and ss.
Step 5: Determine the phenotypic ratios of the backcross offspring.
- Since sepia-eyed (ss) is the recessive trait and red-eyed (s+s) is the dominant trait, the phenotypic ratios will depend on the genotypic ratios.
Step 6: Calculate the genotypic and phenotypic ratios.
- Genotypic ratio: The genotypic ratio will be 1:1 because the s+s male can only produce half s+s offspring and half ss offspring.
- Phenotypic ratio: The phenotypic ratio will also be 1:1 because all offspring with the s+s genotype will have red eyes, and all offspring with the ss genotype will have sepia eyes.
Therefore, the expected genotypic ratio is 1:1 (s+s:ss) and the expected phenotypic ratio is 1:1 (red eye:sepia eye) in the backcross offspring.
To determine the expected phenotypic and genotypic ratios in the backcross of Drosophila, we need to analyze the alleles present in the parental generation and the F1 generation.
Given information:
- Sepia-colored eyes are caused by the recessive allele s.
- Wild type, or red eye color, is caused by the dominant allele s+.
- Sepia-eyed females are crossed with pure wild type males.
Parental generation (first cross):
- Sepia-eyed females (genotype: ss) crossed with pure wild type males (genotype: s+s+).
F1 generation (offspring of the first cross):
- All females will be sepia-eyed since they inherit the recessive allele from the sepia-eyed female parent (genotype: ss).
- All males will have wild-type red eyes since they inherit the dominant allele from their pure wild type male parent (genotype: s+s+).
To determine the expected phenotypic and genotypic ratios in the backcross, we consider the traits and genotypes present in the F1 generation.
Backcross (F1 males x sepia-eyed parental females):
- F1 males (s+s+) are crossed with sepia-eyed parental females (ss).
Now let's determine the possible outcomes and their expected ratios:
1. Phenotypic ratio:
- 100% of the offspring will have sepia-colored eyes since the allele for sepia eye color (s) is recessive. Therefore, all offspring will express the phenotypic trait of sepia eye color.
2. Genotypic ratio:
- 50% of the offspring will be heterozygous for the sepia eye color allele (s+s) since the F1 males carry one dominant allele (s+) and one recessive allele (s) from their parents.
- 50% of the offspring will be homozygous recessive for sepia eye color (ss) since the parental females carry two recessive alleles (s).
Therefore, the expected genotypic ratio in the backcross will be 1:1 (50% s+s : 50% ss).
In summary, the phenotypic ratio will be 100% sepia-colored eyes, while the genotypic ratio will be 50% s+s : 50% ss in the backcross of F1 males to sepia-eyed parental females.