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Human Genetics

Human Genetics. Review – What is a GENE ?. A gene is the unit that controls traits Genes are passed from parents to offspring Genes are located on our chromosomes. KARYOTYPE: A SET OF PHOTOGRAPHS OF CHROMOSOMES GROUPED IN ORDER OF PAIRS.

henry-bernard
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Human Genetics

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  1. Human Genetics

  2. Review – What is a GENE? • A gene is the unit that controls traits • Genes are passed from parents to offspring • Genes are located on our chromosomes

  3. KARYOTYPE: A SET OF PHOTOGRAPHS OF CHROMOSOMES GROUPED IN ORDER OF PAIRS. Karyotypes are used to detect chromosomal disorders and to determine the sex of an unborn child

  4. The first 44 chromosomes (22 pairs) are called autosomes. The 23rd pair of chromosomes are the sex chromosomes which determine an individual’s sex. XX – Female or XY - Male

  5. At least 1 (X) chromosome MUST be present for survival The presence OR absence of the (Y) chromosome determines sex of offspring

  6. Normal Female Karyotype This karyotype would be labeled as: 46,XX

  7. Normal Male Karyotype This karyotype would be labeled as: 46,XY

  8. Chromosome Number Disorders Nondisjunction - Failure of chromosomes to separate during meiosis. • Abnormal offspring • Monosomy: one copy of a chromosome • Trisomy: three copies of a chromosome • Polyploidy: multiple copies of chromosomes

  9. Nondisjunction in Anaphase I

  10. Trisomy 21 (Down Syndrome)

  11. Turner’s Syndrome: 45XO

  12. Klinefelter’s Syndrome: 47XXY

  13. CHROMOSOMAL MUTATIONS Deletion-piece breaks off and is lost.

  14. Duplication- piece breaks off and attaches to a homologous chromosome

  15. Translocation - piece breaks off and attaches to non-homologous chromosome.

  16. Inversion- piece breaks off and reattaches upside-down.

  17. What are Sex-Linked Traits? Trait determined by a gene on a sex chromosome (usually X chromosome). • Females must receive 2 affected X’s in order to have the trait. • Females with only 1 affected X are carriers. • Males will always show a recessive trait located on the X chromosome because he only has 1 X. • Examples: • Colorblindness, Hemophilia, Duchenne’s Muscular Dystrophy

  18. Sex-Linked Disorders • Genotypes for sex-linked traits are written using the X and Y chromosomes to show path of inheritance. C = normal vision c = colorblindness Colorblind male = XcY Colorblind female = XcXc Carrier female = XCXc **Remember males CANNOT be carriers**

  19. Colorblindness

  20. Sex-linked traits: Color blind father x carrier mother ? ? ?

  21. Sex-Linked Punnett Squares • In sex-linked traits, probabilities for male and female offspring must be calculated separately because traits are inherited differently.

  22. Sex-Linked Punnett Square Practice • A colorblind female marries a man with normal vision. What is the probability of them having colorblind children? Key: ________________________________________ Cross: _______________________________________ Probability of having a colorblind daughter = ___________ Probability of having a colorblind son = ____________

  23. Sex-Linked Punnett Square Practice 2. A genetics counselor interviews a couple with a family history of hemophilia to evaluate the possibility of having offspring with the disorder. The wife does not have hemophilia, but states that her father had the disorder. The husband is normal. Key: ________________________________________ Cross: _______________________________________ Probability of having a daughter with hemophilia = ___________ Probability of having a son with hemophilia = ____________

  24. Predictions and People • What is a Pedigree - chart that shows how a trait and the genes that control it are inherited within a family.

  25. How to Read a Pedigree Circle = female Shaded figure = Individuals who are affectedby the trait Square = male Non-shaded = individuals who are unaffected ***Carriers are half shaded*** Horizontal lines connect siblings or spouses Vertical lines connect parents and children **When illustrated in a pedigree, children are placed in birth order from left to right (Oldest to youngest).

  26. What is a Carrier? - an individual who carries a recessive trait (heterozygous) that is not expressed and can pass on genetic disorders to offspring. • Has normal phenotype

  27. How many generations are shown? • How many children did Parents of Generation 1 have? • How many were boys? • How many were girls? • How many children did Parents of Generation II have? • How many were boys? • How many were girls? • 4. Use the key to determine the genotypes of each person in this pedigree. (Hint: label all homozygous recessives first) Practice The following pedigree shows the inheritance of a recessive trait. Key: R = Non-affected; r = affected

  28. I Generation 1 2 II Generation 6 3 5 4 III Generation 7 8 9 10

  29. Widow’s Peak is dominant over no widow’s peak W = dominant w = recessive Ww ww

  30. Many genetic disorders caused by AUTOSOMAL RECESSIVE GENES. Examples: PKU (an inability to break down the amino acid Phenylalanine (can cause mental retardation) Tay-Sachs (results in a nervous system breakdown and death)

  31. ALBINISM - a lack of pigment in hair, skin and eyes. CYSTIC FIBROSIS - caused by a recessive allele on chromosome #7 - causes excess mucous in lungs and digestive tract, increased susceptibility to infections.

  32. Tay-Sachs Recessive Trait Disorder T = normal t = tay-sachs Tt Tt TT tt Tt Tt Tt

  33. Autosomal Dominant Disorders • Dominant allele disorders are less common (typically a homozygous person (HH) dies therefore the trait can't carry on to offspring). • Ex. Huntington Disease

  34. Huntington’s Disease - dominance (H) hh Hh Hh hh AffectedNormal a. No symptoms until 30’s or 40’s b. Nerve damage: loss of muscle control & mental function until death

  35. Huntington’s Disease (dominant trait disorder) H = affected w/disease h = normal Hh Hh HH hh hh Hh Hh

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