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Human Genetics

Chapter 12. Human Genetics. Humans have 46 chromosomes 44 are autosomes 22 pairs of homologous chromosomes 2 are sex chromosomes: X and Y Females have two X chromosomes Males have one X and one Y. Review. Karyotypes : Male and Female.

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Human Genetics

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  1. Chapter 12 Human Genetics

  2. Humans have 46 chromosomes • 44 are autosomes • 22 pairs of homologous chromosomes • 2 are sex chromosomes: X and Y • Females have two X chromosomes • Males have one X and one Y Review

  3. Karyotypes: Male and Female

  4. Many genes not related to sex are on the X chromosome They are called sex-linked traits Example: Drosophila (Fruit fly) eye color Sex-linked traits

  5. Red eyes ( XR ) is dominant White eyes ( Xr ) is recessive Drosophila Eye Color XRXR XrY XRXr XRY XRXr XrY XR Xr XR XR XR Xr Y XRXr XRXR XRXr Y Y Xr Xr XRY XrXR XRY XrXr XRY XrY XrY R = red-eye allele r = white-eye allele

  6. Human sex-linked disorders • Most sex-linked human disorders are due to recessive alleles • Examples: hemophilia, red-green color blindness • These are mostly seen in males • Why??? Figure 9.23A

  7. A male receives a single X-linked allele from his mother, and will have the disorder (XcY) • A female has to receive the allele from both parents to be affected (XcXc) • A female with the gene for the trait on one of her X chromosomes is called a carrier (XcX). • A carrier may not know she carries the gene for the trait until she has a son with the trait. Sex – Linked Inheritance

  8. Hemophilia is a deadly disease in which the individual’s blood does not clot properly. It is caused by a recessive gene on the X chromosome. (Xh) Women can be XX, XXh (carrier), or XhXh (affected). Men can be XY or XhY (affected). Hemophilia

  9. A pedigree is a diagram that shows how a trait is inherited over several generations. Circles represent women, squares are men Solid (dark) is affected (with disease, etc.) Empty (white) is not affected Half filled is a carrier (heterozygous) pedigrees

  10. A high incidence of hemophilia has plagued the royal families of Europe QueenVictoria Albert Alice Louis Alexandra CzarNicholas IIof Russia Alexis Figure 9.23B

  11. Problems • A female has the genotype XX and she marries a man who is color blind (XcY). What is the probability that they will have a child who is color blind?

  12. A female who is not color blind, but whose father was color blind marries a color blind male. What is the probability that they will have a child who is colorblind?

  13. Sex-linked disorders • Affected allele is usually on X chromosome • Autosomal disorders • Can affect men and women equally • Chromosome number disorders • Chromosomes don’t separate evenly in meiosis Human Genetic Disorders

  14. Sex-linked disorders • Colorblindness – Cannot distinguish between red & green • Hemophilia – Blood clotting disorder • Muscular Dystrophy – Muscles weaken and eventually break down.

  15. Autosomaldisorders • Albinism • no hair or skin pigment • Cystic Fibrosis • mucus clogs lungs • Tay-Sachs disease • breaks down nervous system

  16. Sickle-cell anemia • abnormal protein causes RBCs to sickle and clump together • PKU (Phenylketonuria) • Body can’t break down a certain amino acid so toxic substance accumulates • nerve damage, retardation Autosomal disorders

  17. Huntington’s Disease • Autosomal Dominant • Weakness and deterioration of brain • No symptoms appear until middle age • A person might not know he or she had the gene until after having children.

  18. Chromosome Number Disorders • Turner’s Syndrome • X0 (sterile females) • Klinefelter’sSyndrome • XXY (mentally retarded, boy, underdeveloped female characteristics) • Down’s Syndrome • Trisomy 21

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