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Human Genetics

Human Genetics. Chapter 12. Human Genetic Traits. Do you think this trait is dominant or recessive?. Widow’s Peak?. DOMINANT. PTC Tasting. Can you taste the PTC???? DOMINANT. Earlobe Shape?. Is your earlobe attached? Do you think this trait is dominant or recessive?. RECESSIVE.

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Human Genetics

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  1. Human Genetics Chapter 12

  2. Human Genetic Traits • Do you think this trait is dominant or recessive?

  3. Widow’s Peak? DOMINANT

  4. PTC Tasting • Can you taste the PTC???? • DOMINANT

  5. Earlobe Shape? • Is your earlobe attached? • Do you think this trait is dominant or recessive? RECESSIVE

  6. Dimples? DOMINANT

  7. Human Inheritance • Humans - 23 pairs of chromosomes • These are made of about 100,000 genes • Scientists study disease causing genes because they can easily be traced • Pedigree – a family record that shows how a trait is inherited over several generations.

  8. Pedigree A Pedigree of Hemophilia in the Royal Families of Europe

  9. Pedigreepage 299 • Carriers – usually, Heterozygous -do not express the recessive allele, but pass it to their offspring Square = Male Circle = Female No shading = normal Shaded = displays trait Half/Half = Carrier

  10. Pedigree Practice • Construct a family pedigree of two unaffected parents with a child who suffers from cystic fibrosis.

  11. Pedigree Practice • Suppose both parents can roll their tongues but their son cannot. Draw a pedigree showing this trait, and label each symbol with the appropriate genotype.

  12. Pedigree Practice • Describe the pedigree of a boy who has galactosemia. His father has galactosemia, his paternal grandparents are phenotypically normal. His mother and maternal grandparents are both phenotypically normal.

  13. A boy is an albino. His mother is also an albino. His father is phenotypically normal. However, his paternal grandfather is an albino. The other 3 of his grandparents are phenotypically normal.

  14. A brother and a sister both are hemophilic. Neither parent shows this trait, however the maternal grandmother suffers from this disorder. The other grandparents are phenotypically normal.

  15. On Your Own • Page 300 • Mini Lab 11.1 – Investigate Human Pedigrees

  16. Simple Dominant Heredity • Many traits are inherited just as the rule of dominance predicts. • Remember, in Mendelian inheritance, a single dominant allele inherited from 1 parent is all that is needed for a person to show the dominant trait.

  17. Patterns of Inheritance • Traits controlled by a Single Allele • >200 traits are determined by a single dominant allele • Ex. Huntington’s Disease • >250 other traits are determined by homozygous recessive alleles • Ex. Cystic Fibrosis, PKU, blue people in Eastern Kentucky

  18. Sometimes Heredity Follows Different Rules 1. Incomplete Dominance: Appearance of a third phenotype 2. Sex-linked inheritance 3. Codominance: Expression of both alleles

  19. 1. Incomplete Dominance • Incomplete dominance - Cross between organisms with 2 different phenotypes -produces offspring with a 3rd phenotype that is a blending of the parental traits.  • RED Flower x WHITE Flower ---> PINK Flower

  20. R = allele for red flowers W = allele for white flowers red x white ---> pinkRR x WW ---> 100% RW

  21. 2. Sex determination • In humans, the diploid number of chromosomes = 46 (23 pairs) • There are 22 matching pairs of homologous chromosomes called autosomes. • The 23rd pair differs in males and females, they determine the sex of an individual (sex chromosomes) • X females (XX) • Y males (XY) *Complete a punnett square to determine the expected ratio of males to females produced given their possible gamete contribution

  22. Sex-linked inheritance • Traits controlled by genes located on sex chromosomes are called sex-linked traits • Sex-Linked Traits are found only on the X chromosome • Ex. Hemophilia (recessive) • Ex. Patterned Baldness • Homozygous baldness-both will lose hair • Heterozygous-men will lose hair but women will not • Ex. Colorblindness (recessive)

  23. Color Blindness Activty • http://colorvisiontesting.com/ishihara.htm • http://colorvisiontesting.com/online%20test.htm • Draw your family pedigree for color blindness! • Predict what your children genotype could be if: • Boys – you married a woman who carried the trait for being color blind on her X chromosome • Girls – you married a man who was color blind

  24. Patterns of Inheritance • Complete a punnett square to show how the allele for red eye color is a sex-linked trait

  25. 3. Codominance • Codominance - the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms. • Example: red x white ---> red & white spotted

  26. R = allele for red flowers W = allele for white flowers red x white ---> red & white spotted RR x WW ---> 100% RW

  27. Examples of Codominance 1. Roan fur in cattle • Cattle can be: 1. red (RR = all red hairs) 2. white (WW = all white hairs) 3. roan (RW = red & white hairs together)

  28. 2. Human blood type: AB-2 types of protein ("A" & "B") appear together on the surface of blood cells • How to determine Blood Types: • 4 possible blood types (in order from most common to most rare): O, A, B and AB. • O blood type = individual who is homozygous recessive (ii) and does not have an allele for A or B.

  29. Blood types A and B are codominant alleles. • Recessive allele i (for blood type O) is only expressed when 2 recessive alleles are present. • Individuals who have blood type A: • Genotype = IAIA or IAi • Individuals who have blood type B: • Genotype = IBIB or Ibi • Individual who has blood type AB: • Genotype = IAIB • Individual who has blood type O: • Genotype = ii

  30. Human Blood Types

  31. **IMPORTANCE in Real-Life** • Blood transfusion can only take place between 2 people who have compatible types of blood. • Human blood is separated into different classifications because of the varying proteins on the surface of blood cells. • These proteins are there to identify whether or not the blood in the individual's body is it's own and not something the immunity system should destroy.

  32. What is the chance that the couple from question 1 will have a child with type AB blood? *Show me your answers when you are finished. Keep these in your notes! Blood type practiceUse a Punnett Square! • A woman has type A blood. Her father has type O blood. The woman marries a man with type O blood. What is the chance that they will have a child with type A blood?

  33. Sickle Cell Anemia • Read about Codominance on pg. 302-303 • Define Codominance. • Explain Sickle-cell Disease in ½ page. • Complete Data Analysis Lab 11.1 on the bottom ½ of the page.

  34. Sickle Cell Anemia Cont. • A Mutation Story: http://www.teachersdomain.org/resource/tdc02.sci.life.gen.lp_disorder/

  35. Nondisjunction • Nondisjunction is the failure of homologous chromosome pairs to separate properly during meiosis. The result of this error is a cell with an abnormal (too few or too many) number of chromosomes.

  36. Nondisjunction

  37. Activity: Human Karyotype

  38. Patterns of Inheritance • Disorders due toNondisjunction • Monosomy (45 Chromosomes) • Trisomy (47 Chromosomes) • Trisomy-21 (Down Syndrome) • Trisomy-18 (Edwards Syndrome) • Trisomy-13 (Patau) Child with Trisomy 21

  39. Disorders due to Nondisjunction Cont. • Klinefelter’s (XXY)-male w/ some female traits • Turner’s (XO)-female appearance • Single Y chromosome do not survive • Typically Sterile

  40. Environmental Effects • Genes are inherited from parents, but sometimes their expression is modified by environmental factors. • An example is the snowshoe hare we discussed earlier in the year-these hares have dark fur in the summer and white fur in the winter.

  41. Snowshoe Hare

  42. Detecting Human Genetic Disorders • Genetic Screening – examination of genetic makeup • Karyotype: a picture of chromosomes grouped in pairs and arranged in sequence. • Screening of Blood: look for certain proteins • Genetic Counseling-medical guidance informing of problems that could affect their offspring.

  43. Detecting HumanGenetic Disorders • Amniocentesis: removal of small amount of amnionic fluid surrounding the fetus • Chorionic Villi Sampling: tissue that grows between the mother’s uterus and the placenta (between the 8th and 10th week) • Screening Immediately after Birth: • Ex PKU (Phenylketonuria)-body cannot metabolize the amino acid phenylalanine • Special diet lacking phenylalanine

  44. Karyotyping • http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html

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