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By Lisa Marie Meffert, PhD Rice University

BioEd Online. Heredity: Pedigrees- Working Out Inheritance Patterns. By Lisa Marie Meffert, PhD Rice University. Genology - Lee Family of Virginia and Maryland c1886 Apr. 26. Prints and Photographs Division, Library of Congress (LC-USZ62-90145). How is gender determined? (text p 318).

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By Lisa Marie Meffert, PhD Rice University

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  1. BioEd Online Heredity: Pedigrees- Working Out Inheritance Patterns By Lisa Marie Meffert, PhD Rice University Genology - Lee Family of Virginia and Maryland c1886 Apr. 26.Prints and Photographs Division,Library of Congress (LC-USZ62-90145)

  2. How is gender determined? (text p 318) • Recall that in humans the diploid # of chromosomes is 46 (23 pairs) • There are 22 pairs of homologous chromosomes called autosomes • The 23rd pair of chromosomes are different in males and females

  3. How is gender determined? (text p 318) • These two x’mes are called the sex chromosomes. • Indicated by the letters X and Y • Females are homozygous XX • Males are heterozygous XY

  4. Gender determination (cont’d) • Which chromosomes will determine the gender? • The male determines gender • Why? • What is the expected ratio of males to females? • Complete a punnett square (XX x XY)

  5. XX x XY X Y X X XX XY XX XY

  6. Sex Linked Traits • Traits controlled by genes located on the sex chromosomes are called sex linked traits (most often the X chromosome) • Y can’t cover up the effects • Males either have it or not

  7. Sex Linked Traits • Females can have it, not have it or be carriers • Carriers can pass the gene, but do not exhibit the characteristics of the gene • More about this when we talk about pedigrees

  8. Sex Linked Traits

  9. Nondisjunction (p 271) • The events of meiosis usually proceed accurately • Sometimes homologous chromosomes fail to separate properly • Anaphase I – chromosome pairs separate (1 to each daughter cell)

  10. Nondisjunction (p 271) • Nondisjunction – both chromosomes of a homologous pair move to the same pole. • One gamete has an extra chromosome • (n+1) • The other is short one chromosome • (n-1)

  11. Meiotic Nondisjunction at Meiosis I AnimationTokyo Medical University Genetics Animations http://www.ccs.k12.in.us/chsteachers/Amayhew/Biology%20Notes/mutations%20notes_files/image006.jpg

  12. Levels of Genetic Disorders • What are Genetic Disorders? • List of disorders with info

  13. Trisomy • Zygote with one normal gamete and one gamete with extra x’me • 47 x’mes – Down Syndrome • AKA – Trisomy 21 • Organism with an extra chromosome often survives

  14. Monosomy • Organisms are one or more chromosomes short – usually don’t survive • Cause of most chromosomal miscarriages • E.g. Turner syndrome • Tetraploid

  15. Changes in Chromosome Size Fragile –X • Results from a faulty crossover event that results in a longer X chromatid. • A child receiving this chromosome can be male or female but mostly boys because it is a recessive trait to a normal X. • Their faces are longer, • have trouble with gait, • many have learning differences or disabilities and autism-like mannerisms.

  16. http://learn.genetics.utah.edu/content/disorders/whataregd/cdc/http://learn.genetics.utah.edu/content/disorders/whataregd/cdc/ Cri du Chat • 1/20 000 live births, mostly girls • Deletion of chromosome 5

  17. http://learn.genetics.utah.edu/content/disorders/whataregd/williams/index.htmlhttp://learn.genetics.utah.edu/content/disorders/whataregd/williams/index.html William’s Syndrome • 1/7500 births • Deletion of genes on chromosome 7 • Elfin, perfect pitch, trouble spacial relationships, cognitive processing difficulties, aortic defects

  18. Syndromes • Trisomy 21 – Down syndrome • Trisomy 13 – Patau’s syndrome • XO – Turner’s syndrome • XXX – Trisomy X (metafemales) • XXY – Klinefelter’s syndrome • XYY – Jacob’s syndrome • OY – lethal

  19. Turner syndrome – XO monosomy. Dwarfism • Webbed neck • Valgus of elbow. • Amenorrhea

  20. Klinefelter’s Syndrome - Trisomy XXY • testicular atrophy • increase in gonadotropins in urine.

  21. Jacob’s syndrome • Jacob's syndrome is a rare chromosomal disorder that affects males. • It is caused by the presence of an extra Y chromosome. • Males normally have one X and one Y chromosome.

  22. Jacob’s syndrome • However, individuals with Jacob's syndrome have one X and two Y chromosome. • Males with Jacob's syndrome, also called XYY males

  23. Patau’s syndrome

  24. Fig 12.2 - Pedigree Chart • Family history that shows how a trait is inherited over several generations. • Carriers: those heterozygous for a trait. • Can determine if • autosomal (occurs equally both sexes) • sex-linked (usually seen in males) • heterozygous (dominant phenotype) • homozygous (dominantdominant phenotype, recessive recessive phenotype)

  25. Pedigree Symbols (see worksheet 103)

  26. Dominant Pedigree • affected individuals have at least one affected parent • the phenotype generally appears every generation • two unaffected parents only have unaffected offspring

  27. Recessive Pedigree • unaffected parents can have affected offspring • affected progeny are both male and female

  28. Factors to Consider in Pedigrees • Is the trait located on a sex chromosome or an autosome? • Autosomal – not on a sex chromosome • Sex Linkage – located on one of the sex chromosomes • Y-linked - only males carry the trait. • X-linked (recessive) - sons inherit the disease from normal parents • How is the trait expressed? • Dominant - the trait is expressed in every generation. • Recessive - expression of the trait may skip generations.

  29. Pedigree Diagrams: I • Basic Symbols

  30. Pedigree Diagrams: II • Basic Symbols for offspring and the expression of a trait. • The offspring are depicted below the parents. • Filling the symbol with black indicates the expression of the studied trait.

  31. Marfan’s Syndrome: An Example • Expressed in both sexes. • Thus, autosomal. • Expressed in every generation. • Thus, dominant.

  32. Marfan’s: Genotype the Normal Individuals • Assign codes for the alleles. • Code “m” for the recessive normal allele. • Code “M” for the dominant allele for Marfan’s syndrome. • Normal individuals must be “mm.”

  33. Marfan’s: Genotype the Affected Individuals • Affected individuals must have at least one “M.”

  34. Marfan’s: Parent-Offspring Relationships • Possibilities for #1 and #2: Heterozygote (Mm) or homozygous for “M?” • If “MM,” all offspring from a normal mate should be affected. • Therefore, both must be heterozygotes.

  35. Marfan’s: Parental Genotypes Known • “M” must have come from the mother. • The father can contribute only “m.” • Thus, the remaining genotypes are “Mm.”

  36. Albinism: An Example • Expressed in both sexes at approximately equal frequency. • Thus, autosomal. • Not expressed in every generation. • Thus, recessive.

  37. Albinism: Genotype the Affected Individuals • Assign codes for the alleles. • Code “A” for the dominant normal allele. • Code “a” for the recessive allele for albinism. • Affected individuals must be homozygous for “a.” • First generation parents must be “Aa” because they have normal phenotypes, but affected offspring.

  38. Albinism: Genotype the Normal Individuals • Normal individuals must have at least one “A.”

  39. Albinism: Parent-Offspring Relationships • #1 must transmit “a” to each offspring. • The “A” in the offspring must come from the father. • Normal father could be either heterozygous or homozygous for an “A.” **

  40. Albinism: Parental Genotypes are Known • Both parents are heterozygous. • Normal offspring could have received an “A” from either parent, or from both.

  41. Albinism: One Parental Genotype is Known • Only the genotype of the offspring expressing albinism are known. • Normal offspring must have received an “a” from their affected father.

  42. Hairy Ears: An Example • Only males are affected. • All sons of an affected father have hairy ears. • Thus, hairy ears is Y-linked.

  43. Hairy Ears: Female Sex Determination • All females are XX.

  44. Hairy Ears: Male Sex Determination • All males are XY.

  45. Hairy Ears: Gene on the Y Chromosome • Code “H” indicates the allele on the Y chromosome for hairy ears.

  46. Hairy Ears: Wild-Type Allele for Normal Ears • Code “+” indicates the allele on the Y chromosome for normal ears.

  47. Hemophilia: An Example • In this pedigree, only males are affected, and sons do not share the phenotypes of their fathers. • Thus, hemophilia is linked to a sex chromosome–the X. • Expression of hemophilia skips generations. • Thus, it is recessive. Extensive bruising of the left forearm and hand in a patient with hemophilia.

  48. Hemophilia: Expression of the Female Sex Chromosomes • All females are XX.

  49. Hemophilia: Expression of Male Sex Chromosomes • All males are XY.

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