Sex linked genes genetic disorders
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Sex-linked Genes & Genetic Disorders. Unit 5: Genetics Ch. 11-3 & Parts of Ch. 14. Learning Goals. 1. Describe where sex-linked traits are located and and why these traits generally affect men more than women. Give an example of a sex-linked trait.

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Sex-linked Genes & Genetic Disorders

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Sex-linked Genes & Genetic Disorders

Unit 5: Genetics

Ch. 11-3 & Parts of Ch. 14


Learning Goals

  • 1. Describe where sex-linked traits are located and and why these traits generally affect men more than women. Give an example of a sex-linked trait.

  • 2. Describe dominant and recessive disorders and give an example of each.

  • 3. Explain nondisjunction and how it leads to trisomy and monosomy.


Sex-Linked Genes

X Chromosome

  • Some genes are carried on the sex chromosomes (X & Y)

    • XX = female, XY = male

  • Several disorders are carried on the X chromosome

Y Chromosome


  • Because men have only 1 X, they don’t have a “backup” X like women

  • If the X is bad, men have the disease

    • EX: Colorblindness, hemophilia, muscular dystrophy


Color-Blindness

  • Three genes for color vision are located on the X chromosome.

  • In males, a defective version of any one of these genes produces colorblindness.


  • Sex-linked Crosses

    • 1) Must show sex chromosomes for each parent & alleles for each X chromosome

    • 2) Answer must include male or female


Predict Gender & Phenotypes

  • Colorblindness is a recessive trait

  • Geno: Pheno:

    • XCXC

    • XcXc

    • XCXc

    • XCY

    • XcY

Normal Female

Colorblind Female

Normal / Carrier Female

Normal Male

Colorblind Male


Pedigree Charts

  • A chart used to examine the appearance of traits, especially diseases, over several generations.


Genetic Disorders

  • Some genes code for nonfunctional proteins.

  • These cause hereditary diseases.


Dominant Disorders

  • If you have the gene, you have the disease

    • May not show up until later in life, after you’ve had kids and passed it on

    • Huntington disease, Dwarfism


Huntington’s Disease

  • Results in the early death of some neurons in the brain. People loose the ability to control their movements.

  • Symptoms usually don’t start until the 20s to early 30s.

  • The disease is fatal, usually by the late 30s or early 40s.


Recessive Disorders

  • Can remain hidden and skip generations

  • Heterozygous individuals (Rr) are called “carriers”

    • Albinism, cystic fibrosis, Tay-Sachs, phenylketonuria


  • Cystic Fibrosis- Protein does not fold properly. Causes a build up of mucus in the lungs


Chromosomal Disorders

  • 1) Nondisjunction: chromosomes do not separate properly during meiosis

  • The results are cells with abnormal numbers of chromosomes.

    • Cells end up with extra chromosomes (47) or fewer chromosomes (45).


During Meiosis


  • Trisomy: If there are three homologous chromosomes instead of two

    • Down syndrome is caused by trisomy of chromosome 21


Where is the mutation?


Where is the mutation?


  • Monosomy: the cell is missing one chromosome

    • Turner’s syndrome is a female with one “X” chromosome not 2 “X” chromosomes.


  • 2) Alterations in Chromosome Structure

    • Deletion: portion of chromosome is deleted

      • EX: Cri du chat (Cry of the cat)

    • Duplication: piece of chromosome is repeated

      • Ex: Fragile X Syndrome

    • Translocation: piece of chromosome is deleted from one homologous pair and reattached to another homologous pair


Deletion: Cri du chat


Duplication: Fragile X


Translocation


Learning Goals

  • 1. Describe where sex-linked traits are located and why these traits generally affect men more than women. Give an example of a sex-linked trait.

  • 2. Describe dominant and recessive disorders and give an example of each.

  • 3. Explain nondisjunction and how it leads to trisomy and monosomy.


Whiteboard Practice

  • Legend & Parents

  • Punnett Square & Answers


  • Queen Victoria was a carrier of hemophilia (h), a recessive, sex-linked disease. King Edward was normal (H).

    • 1. Make a legend

    • 2. Genotypes of parents?

    • 3 & 4. Show the cross.

    • 5. Give probabilities for both sons and daughters


  • Muscular Dystrophy (d), is a recessive, sex-linked disease. A man who has muscular dystrophy marries a woman who is homozygous normal

    • 1. Make a legend

    • 2. Genotypes of parents?

    • 3 & 4. Show the cross.

    • 5. Give probabilities for both sons and daughters


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