Chromosomal Basis of Inheritance

1. Chromosomal Basis of Inheritance Chapter 15

2. Most genetics work done on fruit flies (little time to observe many generations) • Thomas Morgan - fruit fly eye color. • Wild type (normal) eye color - red. • Mutant - white.

4. Discovered mutant eye color appeared more often in males - some traits sex-linked (carried on sex chromosomes).

6. Chromosomes have hundreds or thousands of genes. • Genes located on same chromosome, linked genes, inherited together - chromosome passed as unit.

7. "A" and "B" are linked due to their occurrence in the same chromosome.  Similarly, "a" and "b" are linked in the other chromosome. http://anthro.palomar.edu/biobasis/images/linked_genes.gif

8. Production of offspring with new combinations of traits inherited from 2 parents - genetic recombination. • Can occur during crossing over - sections of homologous chromosomes exchanged during meiosis I.

10. http://www.genomenewsnetwork.org/gnn_images/whats_a_genome/crossing_over.jpghttp://www.genomenewsnetwork.org/gnn_images/whats_a_genome/crossing_over.jpg

11. Genetic map - list of the loci along the chromosomes. • Further apart genes are, higher probability they will switch places.

13. Sex chromosomes • 2 sex chromosomes - X and Y. • Males – XY, females - XX. • Other species - X-0 system, Z-W system, haplo-diploid system. • Humans - X-Y system like normal chromosomes - 50/50 chance of having male or female.

15. Until embryo is 2 months old - fetus female. • If fetus XY - SRY gene turned on making fetus male.

16. http://www.expectalipil.com/images/fetal_dev_2.jpg

17. Sex chromosomes, have genes for traits other than sex. • Trait recessive - female will only inherit it if both parents pass it on. • Males - 50% chance of inheriting it (only have 1 X chromosome) • Males have higher rate of sex-linked diseases than females.

18. http://www.emc.maricopa.edu/faculty/farabee/biobk/hemophb.gifhttp://www.emc.maricopa.edu/faculty/farabee/biobk/hemophb.gif

19. Muscular dystrophy - sex-linked disease. • Affects far more males than females. • Hemophilia (excessive bleeding) - sex-linked.

20. http://upload.wikimedia.org/wikipedia/en/a/a3/XlinkRecessive.jpghttp://upload.wikimedia.org/wikipedia/en/a/a3/XlinkRecessive.jpg

21. Only 1 X in females turned on. • Other - Barr body - reactivated in ovaries during egg production (to pass genes on). • Females exhibit characteristics from mother, some from father (sex chromosomes only).

22. http://www.columbia.edu/cu/biology/courses/c2005/images/barr_body.19.gifhttp://www.columbia.edu/cu/biology/courses/c2005/images/barr_body.19.gif Barr body replicated, not transcribed

23. Pattern responsible for mosaic of effects (tortoiseshell cats) • Due to patches of cells expressing orange allele, others have nonorange allele.

24. http://www.cas.muohio.edu/~wilsonkg/gene2005/images/f3p27.jpghttp://www.cas.muohio.edu/~wilsonkg/gene2005/images/f3p27.jpg

26. Errors • Errors can occur both in DNA and in chromosomes. • Nondisjunction - homologous chromosomes fail to separate during meiosis I, or chromatids - during meiosis II. • Some gametes receive 2 of same type of chromosome; another gamete receives no copy.

28. Abnormal # of chromosomes - aneuploidy. • Trisomy - gamete receives 3 of same chromosomes (2n + 1). • Monosomy - gamete receives 1 of same chromosome (2n – 1). • Earlier in development - more profound effect - those cells go through mitosis.

30. http://www.musckids.com/health_library/genetics/images/chromosome_j.gifhttp://www.musckids.com/health_library/genetics/images/chromosome_j.gif

31. Organisms with more than 2 complete sets of chromosomes - polyploidy. • Happens more often in plants than animals. • Species with polyploidy usually more normal than aneuploidy (no missing chromosomes)

32. http://emedia.leeward.hawaii.edu/millen/bot130/learning_objectives/lo15/15b_p37b.gifhttp://emedia.leeward.hawaii.edu/millen/bot130/learning_objectives/lo15/15b_p37b.gif

33. A rodent species that is the result of polyploidy

34. Deletion - piece of chromosome broken off during cell division. • Duplication - fragment becomes attached as extra segment to sister chromatid. • Inversion - piece breaks off, turns around, reattaches (backwards). • Translocation - chromosomal fragment joins nonhomologous chromosome.

36. Down syndrome - trisomy (Trisomy 21). • Chromosome 21 - smallest chromosome - individual can survive.

38. Aneuploidy – can occur in sex chromosomes. • Klinefelter’s syndrome - male XXY (nondisjunction) • Trisomy X (XXX) can occur in females. • Monosomy X - Turner syndrome - nondisjunction.

39. http://www.biology.iupui.edu/biocourses/N100/images/klinefelter.gifhttp://www.biology.iupui.edu/biocourses/N100/images/klinefelter.gif

40. http://www.tokyo-med.ac.jp/genet/kry/xok.jpg

41. Deletion disease - cri-du-chat - chromosome 5. • Chronic myologenous leukemia - example of translocation between chromosome 9 and chromosome 22.

42. http://learn.genetics.utah.edu/units/disorders/karyotype/images/criduchat_karyotype.jpghttp://learn.genetics.utah.edu/units/disorders/karyotype/images/criduchat_karyotype.jpg

43. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Ph1Karyotype.gifhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Ph1Karyotype.gif

44. Some traits dependent on who passes alleles (mother or father) • Prader-Willi syndrome caused by deletion on chromosome 15 (father) • Deletion from mother - Angelman syndrome. • Due to genomic imprinting - gene on 1 homologous chromosome silenced, allele on homologous chromosome expressed.

45. http://www.cytopix.com/ImageResizeCache/723578_t2001.5.25.11.38.0_q50_600x450.jpghttp://www.cytopix.com/ImageResizeCache/723578_t2001.5.25.11.38.0_q50_600x450.jpg

46. Some eukaryotic genes located in mitochondria. • These genes all passed from mother to offspring; none of father’s mitochondrial genes passed on.

47. Coloration due to mitochondrial genes