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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

Sex-linked Genes & Genetic Disorders

Unit 5: Genetics

Ch. 11-3 & Parts of Ch. 14


Learning goals
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
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



Color blindness
Color-Blindness X like women

  • 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 X like women

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

    • 2) Answer must include male or female


Predict gender phenotypes
Predict Gender & Phenotypes X like women

  • 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
Pedigree Charts X like women

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


Genetic disorders
Genetic Disorders X like women

  • Some genes code for nonfunctional proteins.

  • These cause hereditary diseases.


Dominant disorders
Dominant Disorders X like women

  • 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
Huntington’s Disease X like women

  • 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
Recessive Disorders X like women

  • Can remain hidden and skip generations

  • Heterozygous individuals (Rr) are called “carriers”

    • Albinism, cystic fibrosis, Tay-Sachs, phenylketonuria


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


Chromosomal disorders
Chromosomal Disorders X like women

  • 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
During Meiosis X like women


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

    • Down syndrome is caused by trisomy of chromosome 21




  • Monosomy X like women: 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 X like women

    • 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
Deletion: Cri du chat X like women



Translocation
Translocation X like women


Learning goals1
Learning Goals X like women

  • 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
Whiteboard Practice X like women

  • Legend & Parents

  • Punnett Square & Answers




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