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Human Genetics

Human Genetics. Chapter 12. Pedigrees. A pedigree is a graphic representation of human inheritance. Squares = males Circles = females Shaded circles/squares = individuals showing the trait being studied. Recessive Heredity.

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Human Genetics

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  1. Human Genetics Chapter 12

  2. Pedigrees • A pedigree is a graphic representation of human inheritance. Squares = males Circles = females Shaded circles/squares = individuals showing the trait being studied.

  3. Recessive Heredity • Most genetic disorders are caused by recessive alleles (must be inherited from both parents) • Traits with recessive alleles usually skip a generation. • Examples – cystic fibrosis, Tay-Sachs disease, phenylketonuria

  4. Simple Dominant Heredity • Only need to be inherited from one parent. • Examples – tongue rolling, attached earlobes, hitchhikers thumb, Huntington’s disease

  5. Incomplete Dominance • The phenotype of the heterozygous is intermediate. • Ex. Red flower (RR) x white flower (rr) = pink flower (Rr) • Ex. Curly Hair (HH) x straight hair (hh) = wavy hair (Hh)

  6. Codominance • Causes the phenotype of both homozygous parents to be produced in heterozygous offspring. • Example: black feather chicken (BB) + white feather chicken (bb) = black and white feather chicken (Bb)

  7. Other Genetic Patterns • Multiple Alleles – traits controlled by more than two alleles. • Sex determination: autosomes (44) – all the other chromosomes sex chromosomes (2) – determine sex XX = female XY = male

  8. Sex-linked traits – traits controlled by genes located on the sex chromosome. * usually occur more in males • Polygenic inheritance – traits controlled by two or more genes (Many alleles) ex. eye color and skin color

  9. CodominanceIn Humans • Sickle-cell Anemia: - most common in black Americans (1 in 12) - the presence of abnormal shaped red blood cells (sickle shaped or half moon) - slow blood flow, block small vesssels, and result in tissue damage - Individuals who are heterozygous, produce both normal and sickle shaped blood cells. (codominance)

  10. Multiple Alleles in Humans • Blood Type: - Gene I has three alleles: IA, IB, i - these three alleles produce four blood types A, B, AB, and O - blood typing is necessary before a person can get a blood transfusion. - blood typing can also help determine parents

  11. Sex-Linked Traits in Humans • Traits that are determined by genes that are carried on the sex chromosomes. • Most are located on the X-chromosome. • Males have these traits more than females • Ex. Colorblindness, hemophilia

  12. Polygenic Inheritance in Humans • Eye Color • Skin color

  13. Changes in Chromosome Numbers • Humans normally have 44 autosomes (22 pairs) - an extra chromosome is called trisomy - Trisomy 21 (extra 21st chromosome) = Down Syndrome • Changes in sex chromosomes: - If there is a Y chromosome, it is male. - If there is an X chromosome, it is female - Extra chromosomes usually mean they are sterile, but can lead normal lives

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