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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? - PowerPoint PPT Presentation
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The Human Genome
Chapter 14
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.
Human Karyotype: Male of Female?
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.
Other animals can be albino too
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
• 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?
14.2 Human Chromosomes
Colorblind Test
Colorblind Test
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 InactivationCoat 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) x X O 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
NONDISJUNCTIONFailure 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
Nondisjunction during meiosis
Down Syndrome
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