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Chapter 14

Chapter 14. The Human Genome. 14.1: Human Heredity . Humans have 46 chromosomes (23 from each parent) 44 chromosomes are autosomes 2 chromosomes are sex chromosomes XX = female XY = male Probability of female or male offspring?

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Chapter 14

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  1. Chapter 14 The Human Genome

  2. 14.1: Human Heredity • Humans have 46 chromosomes (23 from each parent) • 44 chromosomes are autosomes • 2 chromosomes are sex chromosomes • XX = female XY = male • Probability of female or male offspring? • Karyotype: picture of chromosomes arranged by size.

  3. Human Karyotype: Male or Female?

  4. Pedigree • Biologists use pedigrees to study the inheritance of traits from generation to generation. Often used to track diseases.

  5. Blood Type • A and B are co-dominant • O is recessive • AB = Universal Receiver • O = Universal Donor • Phenotype: blood type

  6. Genetic Diseases: Recessive • Phenylketonuria (PKU): Accumulation of phenylalanine disrupts normal brain development; results in mental retardation • Tay-sachs disease: Nerve damage from accumulation of chemical (gangliosides); fatal by age 4 • Albinism: cannot produce melanin (skin pigment), lack of color in hair, skin, and eyes.

  7. Other animals can be albino too

  8. Genetic Diseases: Dominant • Achondroplasia(dwarfism): shortened bone growth • Huntington’s Disease: degeneration of neurons; loss of motor control and cognition

  9. Genetic Diseases: Co-dominant • Sickle cell anemia: Sickle/crescent shaped blood cells; carry less oxygen and can become trapped in small blood vessels

  10. 14.2 Human Chromosomes • What are genes? Where are genes located? • Remember, genes that are closer together are more likely to be inherited together. They are linked. • Sex-linked genes are located on the X and Y chromosomes. • All X-linked alleles are expressed in males, even if they are recessive. Why?

  11. Colorblind Test

  12. Colorblind Test

  13. Inheritance of Colorblindness • Make a cross between a colorblind man (XbY) and a woman with normal vision (XBXB) • Make a cross between a woman who carries the color blind allele (XBXb) and a man with normal vision (XBY). • 1/10 males affected vs. 1/100 females

  14. Other sex-linked disorders • Hemophilia: missing protein for blood clotting, 1/10000 males affected • Duchenne Muscular Dystrophy: weakening and loss of skeletal muscle due to defective gene coding for muscle protein, in U.S. 1/3000 males affected

  15. X-Chromosome Inactivation Coat color in cats:  Black, Orange,  Calico X B X B  = black, female X O X O = orange, female X B X O = calico, female X B Y  = black, male X O Y  = orange, male

  16. CROSSES X B X B(black female) xXO Y  (orange  male)  This explains why all calico cats are female! ALSO:  in any given cell, one of the X's becomes inactive, which randomizes the pattern of orange and black

  17. NONDISJUNCTION Failure of chromosomes to separate in meiosis – results in an egg (sperm) with too many or too few Down Syndrome (trisomy 21) Sex Chromosome Disorders Klinefelter Syndrome (XXY)—men are usually infertile Turner Syndrome (XO)—woman are sterile

  18. Nondisjunction during meiosis

  19. Down Syndrome

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