Genetic Recombination and LINKED GENES (Chapter 15)

1. Genetic Recombination and LINKED GENES (Chapter 15)

2. Chromosome theory of inheritance (ch15): Genes have specific locations (loci) on chromosomes Chromosomes segregate and assort independently Chromosomes tagged to reveal a specific gene (yellow).

3. Genetic Recombination: production of offspring with new combo of genes from parents • If offspring look like parents  parental types • If different from parents  recombinants Genetic Recombination

4. Crosses with two traits • If genes are on different chromosomes, they sort independently

5. If results do NOT follow Mendel’s Law of Independent Assortment, then the genes are probably linked

6. Genes on the same chromosome tend to be inherited together • They are on the same chromosome. Considered to be “linked”.

7. Linked Genes • Alleles of linked genes do not always stay together • Homologous chromosomes often exchange pieces when they pair in meiosis. • New allele combinations greatly increase variation

8. Linked genes: located on same chromosome and tend to be inherited together during cell division. Usually travel together in meiosis

9. Crossing over: explains why some linked genes get separated during meiosis • the further apart 2 genes on same chromosome, the higher the probability of crossing over and the higher the recombination frequency

10. Recombination creates new combination of “linked” alleles • The farther away two genes are on a chromosome from each other, the more likely they will be exchanged during crossing over • The closer together two genes are on a chromosome, the more likely they will travel together

11. Calculating recombination frequency

12. Linkage Map: genetic map that is based on % of cross-over events • 1 map unit = 1% recombination frequency • Express relative distances along chromosome • 50% recombination = far apart on samechromosome or on 2 differentchromosomes

13. Figure 15.18 Some traits aren’t on chromosomes • 1. Extra Nuclear Genes Example: Mitochondria and chloroplasts inheritance- have their own chromosome, own genetic material . • Depends solely on the maternal parent b/c the zygote’s cytoplasm comes from the egg • Example of chloroplast inheritance: variegated four o’ clock plants

14. Some traits aren’t on chromosomes • Epigenetics inheritance refers to any heritable trait that is not determined by DNA Sequences • Example: Genomic Imprinting

15. Genomic Imprinting • Genomic imprinting: phenotypic effect of gene depends on whether from one parent or the other parent (autosome) • Methylation: Methyl groups (-CH3) are added to DNA to inactivate it. Silencing of certain genes that are “stampled with an imprint during gamete formation • Evidence suggest this methylation pattern may be uniquely heritable and affect phenotype only in immediately successive generations.

16. Not All Chromosomes are Created Equal Sex Chromosomes, and sex linked traits

17. Chromosome Number • Chromosomes are homologous ( same allelic genes with loci arranged in the same order)  You get one set from your mom and one set from your dad Total Human Chromosomes: 46 23 Chromosomes 23 Chromosomes

19. ? Do you remember.... Humans have 23 pairs of chromosomes, 46 total. 22 pairs are called autosomes and 1 pair are sex chromosomes. X X X Y = = Male Female It is the presence of a Y chromosome that determines if an individual will be male or not.

20. Sex determination • Male determines the gender in mammals • How so? • Birds are the opposite • Females ZZ, Males ZW

21. Sex determination varies between animals

22. XY XX X X genotype 2:4 = 50% XX X X X X X 2:4 = 50% XY DAD DETERMINES GENDER!!! Y X Y Y X

23. Human Karyotype What sex?

24. Sex chromosomes • Differ in appearance • Only small parts are homologous (carrying same genes) • Sex-linked genes • Found only on one of the sex chromosomes • Only 20 genes on Y • Related to male characteristics • 1500 genes on X • Related to a variety of traits (few are gender-related)

25. Human development • Y chromosome required for development of testes • Embryo gonads indifferent at 2 months • SRY gene: sex-determining region of Y • Codes for protein that regulates other genes

26. Facts about X and Y • Determine sex of individual • X is bigger than Y • They both have other genes • X has genes not found on Y • If a female has a recessive trait she can pass it on to her son

27. Sex-linked genes • Sex-linked gene on X or Y • Females (XX), male (XY) • Eggs = X, sperm = X or Y • All genes on the sex chromosomes are said to be sex-linked • Fathers pass X-linked genes to daughters, but not sons • Males express recessive trait on the single X (hemizygous) • Females can be affected or carrier

28. Sex Linked Traits Sex Linked Traits • Usually show up in males • If a male receives a single X-linked recessive allele from his mother, he will have the disorder; while a female has to receive the allele from both parents to be affected

29. Thomas Hunt Morgan • Drosophila melanogaster – fruit fly • Fast breeding, hundreds of offsprings, 4 pairs of chromosomes (XX/XY) • Sex-linked gene: located on X or Y chromosome • Ex: Fruit fly eye color • Red-eyes called wild-type; white-eyes called mutant • Specific gene carried on specific chromosome

30. Sex-linked inheritance: Eye color in fruit flies PUNNETT SQUARE PRACTICE

31. Eye color for fruit flies • XR = allele for red eyes carried on the X chromosome • Xr = allele for white eyes carried on the X chromosome • Y = the lack of any allele influencing of eye color on the Y chromosome

32. XRXR = female with red eyes (homozygous dominant) • XRXr = female has red eyes (heterozygous) • XrXr= female with white eyes (homozygous recessive) • XRY = male with red eyes • XrY = male with white eyes

33. A red eye heterozygous female is crossed with a red eye male. What are their possible offsprings?

34. XRXr = female has red eyes (heterozygous) XRY = male with red eyes Test cross is XRXr (female) x XRY (male)

35. Set up Punnett Square FEMALE Ma L e Set up Mom and Dad’s sex chromosomes Show mom has heterozygous for colorblindness Fill in offspring

36. Set up Punnett Square FEMALE Ma L e What are the possible genotypes: What are the possible phenotypes

37. Set up Punnett Square FEMALE Ma L e What are the possible genotypes and phenotypes: XRXR :female with red eyes XRXr : female with red eyes XRY : male with red eyes XrY : male with white eyes

38. Sex-linked inheritance: Eye color in fruit flies

39. Transmission of sex-linked recessive traits

40. Example: Cats’ Coat Color The genetic coding for displaying orange coat color (codominant XR) or black color (recessive XB) is found on the X chromosome. The coding for white is a completely separate gene. Since males have only one X chromosome, they can only be orange OR black. GENETICS- Sex linked trait

41. X chromosome inactivation Calico cats (XBXR) are always female 3 colors must be present: black, white and and orange X chromosomes are needed for varying X- inactivation red- and black-based colors, depending on which of its two X chromosomes has been inactivated. tortoiseshell

42. X-Inactivation Barr body= inactive X chromosome; regulate gene dosage in females during embryonic development • Cats: allele for fur color is on X • Only female cats can be tortoiseshell or calico.

43. A woman’s somatic cells have two X chromosomes, while a man's carry only one. If both X chromosomes and all of their genes were to be active in women, they would have twice as many copies of the proteins that they produce in men. This would consequently result in a disequilibrium that would disrupt the finely balanced biochemistry of the human body.Nature ensures this does not happen: one of the X chromosomes is completely and permanently inactivated during a female's early development in the womb. The mechanism responsible for this inactivation is not yet fully understood. However, research into mice has shown that a ribonucleic acid (RNA) molecule called Xist plays a pivotal role in the process. Several hundred copies of this molecule attach themselves to one of the two X chromosomes. Scientists believe that these RNA molecules dock onto other molecules which then inactivate the chromosome. A team of researchers lead by Anton Wutz, Professor of Genetics at ETH Zurich, have now discovered several of these inactivation molecules.

44. Sex Linked Disorders: 1. Duchenne muscular dystrophy-weakening of muscles and loss of coordination 2. Hemophilia 3. Color Blindness http://www.youtube.com/watch?v=w6ccBwnc5KU http://www.youtube.com/watch?v=Pt3wGMcTG2E http://www.youtube.com/watch?v=l3do-AjQA3s

45. Hemophilia • is a rare bleeding disorder that prevents the blood from clotting properly, so a person who has it bleeds more than someone without hemophilia does.

46. A high incidence of hemophilia has plagued the royal families of Europe QueenVictoria Albert Alice Louis Alexandra CzarNicholas IIof Russia Alexis Figure 9.23B

47. Hemophilia-Punnett Practice • XH= normal allele carried on the X chromosome • Xh = hemophilia allele carried on the X chromosome • Y = the lack of any allele influencing hemophilia on the Y chromosome

48. Possible genotypes and their respective phenotypes: • XHXH = female with normal health (homozygous) • XHXh = female is a carrier for the recessive hemophilia allele (heterozygous) • XhXh= female with hemophilia allele (homozygous recessive) • XHY = male with normal health • XhY = male with hemophilia Female symbol Male symbol

49. Hemophilia is an X-Linked Recessive Disorder Hemophiliac Girl x Normal Boy h h H Normal X X X Y H H H h X X h X Y X X H h h h H H X X H X X X X X Hemophilia h h h h h Y X Y X Y X X X Y

50. Boys always get Mom’s X!If Mom has X-linked disorder, boy will get it too! h h X X h h H H H X X X X X h h Y X Y X Y