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Chromosomal Basis of Inheritance Chapter 15. Most genetics work done on fruit flies (little time to observe many generations) Thomas Morgan - fruit fly.

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Presentation on theme: "Chromosomal Basis of Inheritance Chapter 15. Most genetics work done on fruit flies (little time to observe many generations) Thomas Morgan - fruit fly."— Presentation transcript:

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.

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

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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.

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10 http://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.

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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.

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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.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.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.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.jpg

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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.

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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.

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30 http://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.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.

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

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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.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.jpg

43 http://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.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


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