Biology 106 Epistasis, Sex-Linked Traits Answer Each Questio ✓ Solved

Biology 106 Epistasissex Linked Traitsanswer Each Question

Marfan syndrome is a dominant disorder. In the cross Mm x mm, what percentage of the children are expected to inherit the disorder? Explain your answer.

How does non-disjunction cause Down syndrome? What is specifically happening in which process to cause this disorder?

Labrador retrievers coat color is controlled by two genes. For the cross bbEe x BbEe, list the gametes produced by each parent.

What color puppies will this cross produce?

List the percentage for each color from this cross.

Why are there more males with red/green colorblindness than females?

If Xc denotes the colorblindness allele and X denotes the normal vision allele; From the cross XcX x XY What percentage of boys will be colorblind? What percentage of girls will be colorblind?

From the information provided determine the genotypes and phenotypes for all individuals in a pedigree for color blindness within a family.

Using your textbook, notes and this website to answer the pre lab questions.

Define the term sex linked in your own words. List 3 common human sex linked traits. What is the most common sex linked trait in fruit flies? What is the genotype of a colorblind female? Define the genetic usage of the term “carrier”. Can a male be a carrier of an X linked sex linked trait? Why or why not?

Complete all answers in the space provided. Remember to add your last name and first initial to the file name when you save it prior to submitting through Canvas.

Paper For Above Instructions

Understanding Genetic Traits

Marfan syndrome is a genetic disorder caused by mutations in the FBN1 gene that encodes the connective protein fibrillin-1. This disorder follows an autosomal dominant inheritance pattern, meaning that an offspring only needs to inherit one copy of the mutated gene from an affected parent to exhibit the characteristics of the disorder. In the case of a cross between a heterozygous individual (Mm) for Marfan syndrome and a homozygous recessive individual (mm), the potential genotypes of their offspring can be represented as follows:

1. Mm (with Marfan syndrome) - 50%

2. mm (without Marfan syndrome) - 50%

Thus, 50% of the children are expected to inherit Marfan syndrome.

Non-Disjunction and Down Syndrome

Down syndrome is primarily caused by an error in chromosome separation called non-disjunction, which occurs during meiosis. Normally, chromosomes are supposed to separate evenly into gametes; however, during non-disjunction, one gamete receives an extra copy of a chromosome while the other gamete does not receive any copy. This results in a zygote with an abnormal number of chromosomes. Specifically, Down syndrome is typically caused by an extra copy of chromosome 21, leading to the condition known as trisomy 21. This abnormality occurs due to the failure of chromosome 21 to segregate properly, resulting in a total of three copies instead of the usual two in the individual's cells.

Labrador Retriever Coat Color Genetics

In the case of Labrador retrievers, coat color is influenced by two genes: B (black) and E (extension). For the cross bbEe x BbEe, the gametes produced by each parent can be calculated. The male (BbEe) can produce the following gametes: BE, Be, bE, be. The female (bbEe) produces: bE, be.

This results in a possible combination of offspring that could be as follows:

• BBEE - Black
• BBEe - Black
• BbEE - Black
• BbEe - Black
• bbEE - Chocolate
• bbEe - Chocolate
• bbEe - Yellow
• bbEE - Yellow

Based on this cross, we expect the offspring to exhibit coat colors predominantly of black and chocolate, consistent with the dominant traits inherited from the black labrador parent.

Colorblindness and Sex-Linked Traits

The prevalence of red-green colorblindness among males as opposed to females can be attributed to the X-linked inheritance pattern of this trait. Males have only one X chromosome (XY), whereas females have two (XX). This means that if a male inherits the colorblind allele (Xc) from his mother, he will express the trait, whereas females would need to inherit two copies of the colorblind allele (XcXc) to express the same trait. Therefore, in the cross of XcX (carrier female) and XY (normal male), 50% of the sons (XcY) would be colorblind, and 50% of the daughters (XcX) would be carriers (but not colorblind).

Pedigree Analysis for Colorblindness

Pedigrees can be used to identify colorblind genotypes and phenotypes within a family. Males who are affected must carry the colorblind allele on their single X chromosome. Females can either express the trait (XcXc) or be carriers (XcX). Each individual's genotype can be concluded based on their phenotype and their parents' respective traits. We can infer carriers if they pass on the trait to sons without showing symptoms themselves.

Sex-Linked Inheritance Response

Sex-linked traits refer to traits that are associated with genes located on sex chromosomes, typically the X chromosome. Examples of common human sex-linked traits include hemophilia, Duchenne muscular dystrophy, and color vision deficiency. In fruit flies (Drosophila melanogaster), the most common sex-linked trait is the white eye mutation.

A colorblind female must carry the genotype (XcXc), both alleles being for colorblindness. Regarding the term "carrier," it refers to an individual who possesses one recessive allele for a trait but does not exhibit the trait themselves due to the presence of a dominant allele. Unfortunately, males cannot be carriers of X-linked traits since they only have one X chromosome, meaning they express any trait present on it.

References

• Griffiths, A. J. F., et al. (2015). Introduction to Genetic Analysis. W.H. Freeman.
• Hartl, D. L., & Jones, E. W. (2011). Genetics: Analysis of Genes and Genomes. Jones & Bartlett Publishers.
• Snustad, D. P., & Simmons, M. J. (2016). Principles of Genetics. Wiley.
• Hartl, D. L. (2016). Genetics. Jones & Bartlett Learning.
• Klug, W. S., Cummings, M. R., & Spencer, C. A. (2010). Concepts of Genetics. Pearson.
• Bowen, R., & O'Reilly, T. (2017). Sex-linked Traits. Genetic Science Learning Center.
• American Society of Human Genetics. (2020). Genetics Home Reference.
• Cleveland Clinic. (2021). Marfan Syndrome. Retrieved from https://my.clevelandclinic.org/health/diseases/9734-marfan-syndrome
• National Down Syndrome Society. (2020). Understanding Down Syndrome. Retrieved from https://www.ndss.org
• NCBI Bookshelf. (2019). Genetics of Color Vision Deficiency. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK11791/