X-Linked Eye Color Inheritance in Fruit Flies - HS - BIOLOGY - Inheritance and Variation

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6 Nsɛmmisa

Hyɛ no nsow a efi ɔkyerɛwfo no hɔ:

Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.

Akwankyerɛ

Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.

Ɛhia

DOK 1

HS-LS3-1

Ɛhia

DOK 2

HS-LS3-2

Ɛhia

DOK 2

HS-LS3-1

Ɛhia

DOK 3

HS-LS3-1

Ɛhia

DOK 1

HS-LS1-1

Ɛhia

DOK 2

HS-LS3-1

X-Linked Eye Color Inheritance in Fruit Flies

Fruit flies ($Drosophila melanogaster$) are widely used in genetics because they reproduce quickly and show clear, observable traits. One classic trait is eye color. The “wild type” eye color is red, but scientists have identified mutations that produce white eyes. Early experiments by Thomas Hunt Morgan and others showed that the gene controlling this trait is located on the X chromosome, making eye color an example of sex-linked inheritance. This system clearly illustrates how DNA and chromosomes code for traits passed from parents to offspring.

In many animals, including fruit flies, females have two X chromosomes ($XX$) and males have one X and one Y ($XY$). Genes located on the X chromosome show special inheritance patterns because males have only one copy of X-linked genes. For the eye color gene, the normal red-eye allele can be written as $X^R$, and the white-eye allele as $X^r$. Females can be $X^R X^R$, $X^R X^r$, or $X^r X^r$, while males are $X^R Y$ or $X^r Y$.

When a red-eyed female ($X^R X^R$) is crossed with a white-eyed male ($X^r Y$), all $F_1$ offspring receive at least one $X^R$ allele. The female offspring become $X^R X^r$ (red-eyed carriers), and the male offspring become $X^R Y$ (red-eyed). As a result, all $F_1$ flies have red eyes, even though some carry the white allele. However, if $F_1$ flies are crossed with each other - $X^R X^r$ females with $X^R Y$ males - the $F_2$ generation includes both red-eyed and white-eyed flies. Importantly, white eyes appear more often in males, because a male with $X^r Y$ has no second X chromosome to mask the recessive allele.

These patterns reveal the relationship between DNA, chromosomes, and traits. The eye color gene is a DNA sequence on the X chromosome that provides instructions for a pigment-related protein. The red allele produces functional pigment, while the white allele does not. Because males inherit their single X chromosome from their mothers and a Y chromosome from their fathers, they express whichever X-linked allele they receive. Females, with two X chromosomes, can carry a recessive allele without showing the trait.

Diagram 1.

Sex-linked inheritance diagram showing crosses between white-eyed and red-eyed male and female Drosophila, and resulting F1 and F2 offspring phenotypes and genotypes. Source:

https://www.alamy.com/stock-photo-sex-linked-inheritance-of-white-eyes-in-drosophila-flies-24373102.html

Table 1.

Offspring Sex	Eye Color	Number of Offspring
Female	Red	52
Male	Red	48

Graph of Information - Figure 1.

Graph of F1 offspring eye color (all red) by offspring sex

Table 2.

Offspring Sex	Genotype	Eye Color	Number of Offspring
Female	X+X+	Red	25
Female	X+Xw	Red	27
Male	X+Y	Red	23
Male	XwY	White	21

Graph of Information - Figure 2.

Graph of F2 offspring eye color distribution by phenotype

Ɛhia

Which statement best explains why male fruit flies are more likely than females to express the white-eye phenotype?

Males receive two X chromosomes, so mutations appear twice as often.

Males have only one X chromosome, so any recessive allele is expressed.

Males inherit their eye color allele only from their fathers.

Males cannot carry recessive alleles.

DOK 1

HS-LS3-1

Ɛhia

Based on the F1 and F2 data tables, explain how the appearance of white-eyed males in the F2 generation demonstrates the role of allele combinations in trait expression.

DOK 2

HS-LS3-2

Ɛhia

Using Table 2, compare the number of red-eyed females and white-eyed males in the F2 generation. What pattern do you observe, and how does this pattern support X-linked inheritance?

DOK 2

HS-LS3-1

Ɛhia

How does the location of the eye-color gene on the X chromosome explain the distribution of red- and white-eyed offspring in the F2 generation?
Respond using a Claim, Evidence, and Reasoning (CER) structure.

DOK 3

HS-LS3-1

Ɛhia

Which statement best describes how the DNA sequence of the eye-color gene leads to the differences between the red and white phenotypes?

The DNA sequence determines which chromosome the allele attaches to.

The DNA sequence provides instructions for a pigment-producing protein.

The DNA sequence changes depending on the sex of the fly.

The DNA sequence is identical in all flies, regardless of phenotype.

DOK 1

HS-LS1-1

Ɛhia

Refer to Table 1 and Figure 1. Explain why all F1 offspring show red eyes, even though the white-eye allele is present in the cross.

DOK 2

HS-LS3-1

X-Linked Eye Color Inheritance in Fruit Flies

Diagram 1.

Sex-linked inheritance diagram showing crosses between white-eyed and red-eyed male and female Drosophila, and resulting F1 and F2 offspring phenotypes and genotypes. Source:

https://www.alamy.com/stock-photo-sex-linked-inheritance-of-white-eyes-in-drosophila-flies-24373102.html

Table 1.

Offspring Sex	Eye Color	Number of Offspring
Female	Red	52
Male	Red	48

Graph of Information - Figure 1.

Graph of F1 offspring eye color (all red) by offspring sex

Table 2.

Offspring Sex	Genotype	Eye Color	Number of Offspring
Female	X+X+	Red	25
Female	X+Xw	Red	27
Male	X+Y	Red	23
Male	XwY	White	21

Graph of Information - Figure 2.

Graph of F2 offspring eye color distribution by phenotype

X-Linked Eye Color Inheritance in Fruit Flies - HS - BIOLOGY - Inheritance and Variation

X-Linked Eye Color Inheritance in Fruit Flies

Which statement best explains why male fruit flies are more likely than females to express the white-eye phenotype?

Based on the F1 and F2 data tables, explain how the appearance of white-eyed males in the F2 generation demonstrates the role of allele combinations in trait expression.

Using Table 2, compare the number of red-eyed females and white-eyed males in the F2 generation. What pattern do you observe, and how does this pattern support X-linked inheritance?

How does the location of the eye-color gene on the X chromosome explain the distribution of red- and white-eyed offspring in the F2 generation?Respond using a Claim, Evidence, and Reasoning (CER) structure.

Which statement best describes how the DNA sequence of the eye-color gene leads to the differences between the red and white phenotypes?

Refer to Table 1 and Figure 1. Explain why all F1 offspring show red eyes, even though the white-eye allele is present in the cross.

X-Linked Eye Color Inheritance in Fruit Flies

Which statement best explains why male fruit flies are more likely than females to express the white-eye phenotype?

Based on the F1 and F2 data tables, explain how the appearance of white-eyed males in the F2 generation demonstrates the role of allele combinations in trait expression.

Using Table 2, compare the number of red-eyed females and white-eyed males in the F2 generation. What pattern do you observe, and how does this pattern support X-linked inheritance?

How does the location of the eye-color gene on the X chromosome explain the distribution of red- and white-eyed offspring in the F2 generation?Respond using a Claim, Evidence, and Reasoning (CER) structure.

Which statement best describes how the DNA sequence of the eye-color gene leads to the differences between the red and white phenotypes?

Refer to Table 1 and Figure 1. Explain why all F1 offspring show red eyes, even though the white-eye allele is present in the cross.

How does the location of the eye-color gene on the X chromosome explain the distribution of red- and white-eyed offspring in the F2 generation?
Respond using a Claim, Evidence, and Reasoning (CER) structure.

How does the location of the eye-color gene on the X chromosome explain the distribution of red- and white-eyed offspring in the F2 generation?
Respond using a Claim, Evidence, and Reasoning (CER) structure.