1 / 22

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.

donnel
Download Presentation

Complex Inheritance and Human Heredity

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related