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Complex Inheritance and Human Heredity

Complex Inheritance and Human Heredity. Unit 8.2. 8. 2 Objectives. Distinguish between various complex inheritance patterns. Analyze sex-linked inheritance patterns. Explain how the environment can influence the phenotype of an organism. Incomplete Dominance.

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Complex Inheritance and Human Heredity

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  1. Complex Inheritance and Human Heredity Unit 8.2

  2. 8. 2 Objectives • Distinguish between various complex inheritance patterns. • Analyze sex-linked inheritance patterns. • Explain how the environment can influence the phenotype of an organism.

  3. Incomplete Dominance • For some traits, the dominant allele does not hide the presence of the recessive in heterozygous individuals. • In snapdragons; Red flowers x white flowers = pink flowers

  4. Codominance • No dominant allele • No recessive allele • Both alleles are shown equally • In horses and cows: • Red coat x white coat = ROAN (red and white coat)

  5. Codominance • Sickle-cell disease • Common in people of African descent • Affects red blood cells and their ability to carry oxygen • Normal – disc-shaped red blood cells • Diseased – crescent-moon-shaped red blood cells • Heterozygous – both shapes (no symptoms of the disease) • Also immune to malaria

  6. Codominance • Sickle shaped cells do not last as long, causing anemia • They also do not carry oxygen as efficiently • Sickle shaped cells do not flow well through capillaries, causing clots, pain, fever, etc.

  7. Multiple Alleles • Human blood type is determined by three alleles • IA • IB • I • Blood type determines who you can give blood to or receive blood from

  8. Multiple Alleles

  9. Multiple Alleles • Coat color in rabbits • Multiple alleles can demonstrate different levels of dominance. • In rabbits, four alleles code for coat color: • C,cch,ch,and c. Himalayan (chchorchc) Chinchilla (cchcch or cchch or cchc) Albino (cc) Full color (C_)

  10. Epistasis • Allele of one characteristic hides the effects of an allele for another characteristic. • Example: coat color in Labrador retrievers. • E – fur has dark pigment; e – no dark pigment in fur • B – black pigment; b = brown pigment eebb eeB_ E_bb E_B_ Dark pigment present in fur No dark pigment present in fur

  11. Epistasis • So what happens if two black Labs with the genotypes EeBb have puppies? 9/16 or 56.25% Black 3/16 or 18.75% Chocolate 4/16 or 25% Golden

  12. Sex Determination • Sex chromosomes (homologous pair #23) determine an individual’s gender. • Females = XX • Males = XY (father determines child’s gender) • Autosomes – all other chromosomes (pairs #1-22) X Y

  13. Dosage Compensation • Females technically have more DNA because they have two X chromosomes • X chromosome is larger than Y chromosome • X chromosome carries many genes necessary for the development of males and females. Y chromosome genes relate to male development • To create a balance, one X chromosome stops working in each cell of a female (sometimes called X-inactivation) • Which X chromosome stops working is random • Some “inactivated genes” continue to work anyway

  14. Dosage Compensation • Calico cats • Heterozygous females have genes for black fur and orange fur. • If X chromosome with black gene is inactive, then fur patches will be orange • If X chromosome with orange gene is inactive, then fur patches will be black • Sweat glands in human females

  15. Dosage Compensation • Barr Bodies • Inactivated X chromosome • Condensed, dark masses attached to the inside of the nucleus • A woman can inherit several extra X chromosomes with no affect to her genetics • All extra X chromosomes become inactive and form Barr bodies

  16. Sex-Linked Traits • Traits controlled by genes on the X chromosome • Since males only have one X chromosome, they only need to inherit one allele to receive a recessive trait • Example – Red-green colorblindness • XBY = Normal vision male • XbY = Colorblind male • XBXB = Normal vision female • XBXb = Carrier female with normal vision • XbXb = Colorblind female

  17. Sex-Linked Traits • Red-green colorblindness • 8% of U.S. males Normal vision Colorblind What number do you see?

  18. Sex-Linked Traits • Hemophilia • Delayed clotting of the blood • Cuts continue to bleed • Bruises continue to spread • Must receive an injection of the necessary proteins in order to stop bleeding • Spread through the family of Queen Victoria of England (1819 – 1901), who was a carrier herself

  19. Sex-Linked Traits

  20. Polygenic Traits • Multiple pairs of genes determine the phenotype, resulting in a range of traits. • Examples: skin color, hair color, hair curliness, eye color, etc.

  21. Environmental Influence • Heart disease is genetic, but diet and exercise can reduce the risk. • Sunlight and water can influence a plant’s ability to produce flowers. • Temperature determines gender of some reptiles. • Nile crocodile eggs • Female - < 31.7C • Male – 31.8 C – 34.4 C • Female - > 34.4C

  22. Twin Studies • Helps scientists distinguish between genetic contributions and environmental contributions. • Traits that appear frequently in identical twins are at least partially controlled by heredity. • Traits expressed differently by identical twins are strongly influenced by environment. • MZ = identical twins • DZ = fraternal twins

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