Question

scan in the qr code or click the link below to read about gene linkage. then answer the questions below. for the fill in the blank statements in #1, 3, and 5, rewrite the statement in its entirety on your answer sheet.

https://learn.genetics.utah.edu/content/pigeons/sexlinkage/

1. sex linkage applies to genes that are located on the ____ ____.
2. explain the difference between sex chromosomes and other chromosomes.
3. in meiosis, female mammals make ____ which always have an __. male mammals make __ which can have either an __ or ____.
4. egg and sperm join in fertilization to make a zygote. which parent determines the gender of the offspring? how do you know?

(skip \sex chromosomes in pigeons\)

1. genes code for ____ and __ make ____.
2. give 3 examples of sex-linked disorders in humans. in which gender are they more common? why is that?
3. how many working copies of the colorblind gene do you need to be able to see red and green?
4. what are the odds of being colorblind in boys vs. girls?
5. which chromosomes do not usually go through genetic recombination? why is that?
6. gene linkage is different from sex-linked. based on the picture on this page, which 2 genes would most likely be inherited together? what about least likely?

Explanation:

Define sex linkage

Using the Sex Linkage knowledge point, we identify where sex-linked genes reside. Sex linkage refers specifically to genes located on the sex chromosomes (the X or Y chromosomes).

Compare chromosome types

We distinguish sex chromosomes from autosomes. Sex chromosomes determine an individual's biological sex, whereas autosomes carry genes for general somatic characteristics.

Analyze gamete production

Using the Sex Determination knowledge point, we examine mammalian meiosis. Female mammals (XX) produce eggs containing only X chromosomes. Male mammals (XY) produce sperm carrying either an X or a Y chromosome.

Determine offspring gender

We analyze which parent determines biological sex. Since eggs always carry an X chromosome, the sperm (carrying either X or Y) determines the offspring's gender.

Describe gene expression

We trace how genes determine traits. Genes code for proteins, and proteins make phenotypes (or physical traits).

Identify sex-linked disorders

We list common human X-linked recessive disorders: hemophilia, red-green colorblindness, and Duchenne muscular dystrophy. They are more common in males because males have only one X chromosome.

Determine colorblindness genetics

We find the required working copies of the colorblind gene. Since it is an X-linked recessive trait, you need at least one working copy to have normal vision.

Compare colorblindness odds

We compare the probability of colorblindness between genders. The odds are much higher in boys (about 1 in 12) than in girls (about 1 in 200).

Explain recombination limits

We identify chromosomes that do not recombine. The Y chromosome (specifically the non-homologous region) does not undergo recombination because it lacks a homologous partner in males.

Analyze gene linkage

We evaluate linkage based on physical distance. Genes located very close together on the same chromosome are most likely to be inherited together, while genes far apart are least likely.

Answer:

Question 1

Sex linkage applies to genes that are located on the sex chromosomes.

Question 2

Sex chromosomes (such as X and Y in mammals) determine the biological sex of an individual and carry sex-linked traits. Other chromosomes (autosomes) carry genes for general body characteristics and do not determine sex.

Question 3

In meiosis, female mammals make eggs which always have an X chromosome. Male mammals make sperm which can have either an X or a Y chromosome.

Question 4

The father (male parent) determines the gender of the offspring. This is because the mother's egg always contributes an X chromosome, while the father's sperm can contribute either an X chromosome (resulting in a female, XX) or a Y chromosome (resulting in a male, XY).

Question 5

Genes code for proteins and proteins make traits.

Question 6

Three examples of sex-linked disorders in humans are hemophilia, red-green colorblindness, and Duchenne muscular dystrophy. These disorders are more common in males because they are X-linked recessive traits; males only have one X chromosome, so a single mutated allele causes the disorder.

Question 7

You need at least one working copy of the colorblind gene to be able to see red and green normally.

Question 8

The odds of being colorblind are much higher in boys than in girls. Approximately 8% of boys (1 in 12) are colorblind, compared to only about 0.5% of girls (1 in 200).

Question 9

The Y chromosome (specifically the non-recombining region of the Y chromosome) does not usually undergo genetic recombination. This is because it does not have a homologous partner to pair and cross over with during male meiosis.

Question 10

Based on gene linkage, genes that are physically closest to each other on the same chromosome are most likely to be inherited together. Genes that are furthest apart on the same chromosome (or on different chromosomes) are least likely to be inherited together.