1 / 66

Chapter 15 The Chromosomal Basis of Inheritance

Chapter 15 The Chromosomal Basis of Inheritance. Timeline. 1866- Mendel's Paper 1875- Mitosis worked out 1890's- Meiosis worked out 1902- Sutton, Boveri et. al . connect chromosomes to Meiosis. Sutton. Developed the “Chromosome Theory of Inheritance”.

dorit
Download Presentation

Chapter 15 The Chromosomal Basis of Inheritance

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. Chapter 15 The Chromosomal Basis of Inheritance

  2. Timeline • 1866- Mendel's Paper • 1875- Mitosis worked out • 1890's- Meiosis worked out • 1902- Sutton, Boveri et. al. connect chromosomes to Meiosis.

  3. Sutton • Developed the “Chromosome Theory of Inheritance”. • Mendelian factors or alleles are located on chromosomes. • Chromosomes segregate and show independent assortment.

  4. Morgan • Chose to use fruit flies as a test organism in genetics. • Allowed the first tracing of traits to specific chromosomes.

  5. Fruit Fly • Drosophila melanogaster • Early test organism for genetic studies.

  6. Reasons • Small • Cheap to house and feed • Short generation time • Many offspring • Few chromosomes

  7. Genetic Symbols • Mendel - use of uppercase or lowercase letters. T = tall t = short • Morgan: symbol from the mutant phenotype. + = wild phenotype

  8. Examples • Recessive mutation: • w = white eyes • w+ = red eyes • Dominant Mutation • Cy = Curly wings • Cy+ = Normal wings

  9. Morgan Observed: • A male fly with a mutation for white eyes.

  10. Morgan crossed • The white eye male with a normal red eye female.

  11. The F1 offspring: • All had red eyes. • This suggests that white eyes is a genetic _________? • Recessive.

  12. F1 X F1 = F2 • Morgan expected the F2 to have a 3:1 ratio of red:white • He got this ratio, however, all of the white eyed flies were MALE. • Therefore, the eye color trait appeared to be linked to sex.

  13. Morgan discovered: • Sex linked traits. • Genetic traits whose expression are dependent on the sex of the individual.

  14. Fruit Fly Chromosomes

  15. Sex linked traits • Sex linked traits in humans will be covered in a few minutes.

  16. Morgan Discovered • There are many genes, but only a few chromosomes. • Therefore, each chromosome must carry a number of genes together as a “package”.

  17. Linked Genes • Traits that are located on the same chromosome. • Result: • Failure of Mendel's Law of Independent Assortment. • Ratios mimic monohybrid crosses.

  18. Body Color and Wing type

  19. Example b+b vg+vg X bb vgvg (b+ linked to vg+) (b linked to vg) If unlinked: 1:1:1:1 ratio. If linked: ratio will be altered.

  20. Crossing-Over • Breaks up linkages and creates new ones. • Recombinant offspring formed that doesn't match the parental types.

  21. If Genes are Linked: • Independent Assortment of traits fails. • Linkage may be “strong” or “weak”.

  22. Linkage Strength • Degree of strength related to how close the traits are on the chromosome. • Weak - farther apart • Strong - closer together

  23. Genetic Maps • Constructed from crossing-over frequencies. • 1 map unit = 1% recombination frequency.

  24. Comment - only good for genes that are within 50 map units of each other. Why?

  25. Genetic Maps • Have been constructed for many traits in fruit flies, humans and other organisms.

  26. Sex Linkage in Biology • Several systems are known: • Mammals – XY and XX • Diploid insects – X and XX • Birds – ZZ and ZW • Social insects – haploid and diploid

  27. Homework • Read parts of Chapter 15 • Lab – Genetics of Organisms • Chapter 48 – part II • Chapter 15 Homework • Due in by Dec. 12th noon

  28. Chromosomal Basis of Sex in Humans • X chromosome - medium sized chromosome with a large number of traits. • Y chromosome - much smaller chromosome with only a few traits.

  29. Human Chromosome Sex • Males - XYFemales - XX • Comment - The X and Y chromosomes are a homologous pair, but only for a small region at one tip.

  30. SRY • Sex-determining Region Y chromosome gene. • If present - male • If absent - female • SRY codes for a cell surface receptor.

  31. Sex Linkage • Inheritance of traits on the sex chromosomes. • X- Linkage (common) • Y- Linkage (very rare if exists at all)

  32. Males • Hemizygous - 1 copy of X chromosome. • Show ALL X traits (dominant or recessive). • More likely to show X recessive gene problems than females.

  33. X-linked Disorders • Color blindness • Duchenne's Muscular Dystrophy • Hemophilia (types a and b)

  34. Samples of X-linked patterns:

  35. X-linked Patterns • Trait is usually passed from a carrier mother to 1/2 of sons. • Affected father has no affected children, but passes the trait on to all daughters who will be carriers for the trait.

  36. Comment • Watch how questions with sex linkage are phrased: • Chance of children? • Chance of males?

  37. Can Females be color-blind? • Yes, if their mother was a carrier and their father is affected.

  38. Y-linkage • Hairy ear pinnae. • Comment - new techniques have found a number of Y-linked markers that can be shown to run in the males of a family. • Ex: Jewish priests

  39. Sex Limited Traits • Traits that are only expressed in one sex. • Ex – prostate gland

  40. Sex Influenced Traits • Traits whose expression differs because of the hormones of the sex. • These are NOT on the sex chromosomes. • Ex. – beards, mammary gland development, baldness

  41. Baldness • Testosterone – the trait act as a dominant. • No testosterone – the trait act as a recessive. • Males – have gene = bald • Females – must be homozygous to have thin hair.

More Related