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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

slide4

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
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.
slide7
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
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
Pedigree Charts
  • A chart used to examine the appearance of traits, especially diseases, over several generations.
genetic disorders
Genetic Disorders
  • Some genes code for nonfunctional proteins.
  • These cause hereditary diseases.
dominant disorders
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
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
Recessive Disorders
  • Can remain hidden and skip generations
  • Heterozygous individuals (Rr) are called “carriers”
    • Albinism, cystic fibrosis, Tay-Sachs, phenylketonuria
chromosomal disorders
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).
slide20

Trisomy: If there are three homologous chromosomes instead of two

    • Down syndrome is caused by trisomy of chromosome 21
slide24

Monosomy: the cell is missing one chromosome

    • Turner’s syndrome is a female with one “X” chromosome not 2 “X” chromosomes.
slide26

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
learning goals1
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
Whiteboard Practice
  • Legend & Parents
  • Punnett Square & Answers
slide32

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
slide33

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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