Dihybrid Crosses - Learnexams

Dihybrid Crosses – Problem 2 THIS ONE ISN’T REAL (DOG EARS / COLORING ISN’T CONTROLLED BY A SINGLE GENE!) The allele for floppy ears (F) is dominant over the allele for pointed ears. The allele for grey markings (G) is dominant over the allele for brown markings. STEP 2 Parent 1 is homozygous recessive for ear type and homozygous dominant for fur markings. Parent 2 is heterozygous for both traits. Work out the possible offspring genotypes and phenotypes and give the expected probability of each phenotype. WORK OUT THE PARENT GENOTYPES AND GAMETE ALLELES. FOIL reminder! Outer STEP 1 Parent 1 genotype: Parent 1 gametes: FG, F4,FG Parent 2 genotype: Fr Parent 2 gametes

The Correct Answer and Explanation is :

Let’s work through this Dihybrid cross problem step by step.

STEP 1: Determining the Parent Genotypes

Parent 1

Ear type: Parent 1 is homozygous recessive for ear type, meaning their genotype is ff (for pointed ears).
Markings: Parent 1 is homozygous dominant for fur markings, meaning their genotype is GG (for grey markings).

So, Parent 1 genotype = ffGG.

Parent 2

Ear type: Parent 2 is heterozygous for ear type, meaning their genotype is Ff (for floppy ears).
Markings: Parent 2 is also heterozygous for fur markings, meaning their genotype is Gg (for grey markings).

So, Parent 2 genotype = FfGg.

STEP 2: Gametes

The gametes for each parent are determined by their genotypes. Each gamete carries one allele for each gene (ear type and fur markings). We can use the FOIL method to break down the gametes.

Parent 1 gametes
Since Parent 1 is homozygous ffGG, all their gametes will have the same alleles for each trait:

For ear type: f
For markings: G

So, Parent 1 gametes = fG.

Parent 2 gametes
Parent 2 has the genotype FfGg. Using FOIL:

For ear type: F and f
For markings: G and g

So, Parent 2 gametes = FG, Fg, fG, fg.

STEP 3: Punnett Square

Now we’ll set up the Punnett square to determine the possible offspring genotypes. Parent 1 contributes fG, and Parent 2 contributes FG, Fg, fG, or fg.

	FG	Fg	fG	fg
fG	FfGG	FfGg	ffGG	ffGg

Step 4: Genotypes of Offspring

From the Punnett square, we get the following genotypes for the offspring:

FfGG (Floppy ears, Grey markings)
FfGg (Floppy ears, Grey markings)
ffGG (Pointed ears, Grey markings)
ffGg (Pointed ears, Grey markings)

Step 5: Phenotypic Ratio

Now, let’s determine the phenotypes based on the genotypes:

Floppy ears (dominant F) will appear in any offspring that have at least one F allele. So, the FfGG and FfGg offspring will have floppy ears.
Pointed ears (recessive f) will only appear in offspring that have two f alleles. So, the ffGG and ffGg offspring will have pointed ears.
Grey markings (dominant G) will appear in any offspring with at least one G allele. All offspring in this case will have grey markings, because all combinations have at least one G.

Thus, the phenotypic ratio is:

2 Floppy ears, Grey markings (FfGG, FfGg)
2 Pointed ears, Grey markings (ffGG, ffGg)

Expected Probability:

Probability of Floppy ears, Grey markings = 2/4 = 50%
Probability of Pointed ears, Grey markings = 2/4 = 50%

Summary Explanation:

In this dihybrid cross, the possible genotypes of the offspring result from combining the alleles from each parent. The alleles for ear type and fur markings are inherited independently, following Mendelian inheritance patterns. Since the ear type and fur markings are determined by dominant and recessive alleles, the expected phenotypic ratio for the offspring is 50% with floppy ears and grey markings, and 50% with pointed ears and grey markings.