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Chapter 14 delves into the complexities of human heredity, explaining the structure and function of chromosomes with 46 total (23 from each parent). It covers genetic inheritance through karyotypes and pedigrees, highlighting the role of sex chromosomes and the probability of offspring gender. The chapter explores various genetic diseases, including recessive disorders like PKU and dominant disorders like Huntington's. It discusses co-dominance using sickle cell anemia and examines sex-linked traits, using examples like colorblindness and hemophilia, while addressing issues like nondisjunction and associated syndromes.
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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? • Karyotype: picture of chromosomes arranged by size.
Pedigree • Biologists use pedigrees to study the inheritance of traits from generation to generation. Often used to track diseases.
Blood Type • A and B are co-dominant • O is recessive • AB = Universal Receiver • O = Universal Donor • Phenotype: blood type
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.
Genetic Diseases: Dominant • Achondroplasia(dwarfism): shortened bone growth • Huntington’s Disease: degeneration of neurons; loss of motor control and cognition
Genetic Diseases: Co-dominant • Sickle cell anemia: Sickle/crescent shaped blood cells; carry less oxygen and can become trapped in small blood vessels
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?
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
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
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
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
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
