biol139-lecture13-2011 - Next topic Next Chromosomes...

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Unformatted text preview: Next topic Next Chromosomes Chapter 4 Chapter pp 83 - 88 pp pp 39 - 66 iGenetics pp Chromosomes and reproduction Chromosomes Earliest indications : 1667 studies showing semen contains spermatozoa 1854 studies with frogs and sea urchins showing union of male and female gametes. Equal contribution. 1879 observation of threadlike structures in the nuclei of salamander cells during cell division 1880s, advances in microscopic techniques, 1880s, use of dyes for differential staining of cytoplasm, nucleus and nuclear structures, including nucleus chromosomes chromosomes Early 1900s, linking chromosomes to the Mendelian principles of segregation and independent assortment. • Proposed each egg or sperm contains only ONE of each chromosome of a pair each This work inspired the chromosomal theory of inheritance This chromosomal This theory states that hereditary information is on genes and that genes are located on chromosomes genes Also that egg and sperm contribute equally to the Also egg to genetic endowment of offspring • through their nuclei through 1901 – found the X and Y chromosomes determine sex in grasshoppers (they have a total of 24 chromosomes in their cells.. Excluding those of gametes egg and sperm) Chromosomes in the cells of grasshopper: • 22 of these occur in 11 matched pairs (autosomal) • 2 of these were unmatched (sex chromosomes) • called the larger one X and smaller one Y Gametes on the other hand had ½ the # of chromosomes • sperm had 11 chromosomes (autosomes) and either an X or a Y (sex chromosome) • eggs had 11 chromosomes and an X only When fertilization occurs a female carries two of the same sex chromosomes (XX), and males carry one of each (XY) Sutton concluded the X and Y determine gender and soon others confirmed presence of separate sex chromosomes in other species If certain chromosomes have information to determine gender, then why can’t other chromosomes in the body carry information also? This is a chromosome! Matched pair of chromosomes Like grasshopper with 12 chromosomes (11 chromosomes (1 of each matched pair + 1 sex chromosome) in gametes They are haploid state Like grasshopper with 24 chromosomes (11 matched pairs + sex chromosomes) in cells of body They are diploid state Metaphase chromosomes Metaphase Thickened, condensed, duplicated chromosomes Homologous chromosomes: Homologous • members of a chromosome pair chromosome • contain same genes (one mother, one father) genes • vary in alleles of gene between homologs alleles • pair at meiosis pair • called homologs called Sister Chromatids • identical alleles Nonhomologous chromosomes: • contain different genes contain • do not pair at meiosis do Electron micrograph of a metaphase chromosome Electron Sister chromatids Duplicated sister chromatids, ready for mitosis (DNA replication has occurred) Karyotype Karyotype Homologous chromosomes • match in size, shape • banding pattern 2n = 46 n = 23 The visual description of a complete set of chromosomes in one cell of an organism. Always uses metaphase chromosomes. How many chromatids? (23 x 4) = 92 (23 How How many chromosomes? (23 x 2) = 46 (2n) (23 How How many non-homologous chomosomes? 23 (n) (X and Y are a pair) Detecting chromosomes with fluorescent probes Detecting Chromosomes and reproduction Chromosomes How are genes transmitted from organism to organism and how do their numbers remain consistent? Two major processes: Mitosis: nuclear division that results in 2 daughter cells Mitosis: nuclear each containing identical numbers of chromosomes of as the parent cell Meiosis: division that results in each egg and sperm division cells containing 1/2 the number of chromosomes found cells 1/2 found in other cells (somatic) Diploid versus haploid cells Diploid 2N = diploid Somatic Cells (soma = body) Mitosis: 2N = 8 Remains constant from cell to cell Meiosis: 2N = 8 goes to N = 4 N = haploid Gamete Cells (egg and sperm) One Chromosome Pair Determines an Individuals One 46 chromosomes or 23 pairs Sex Diploid 2n= 46 22 autosomal pairs + XX (sex) 22 autosomal pairs + XY (sex) meiosis meiosis 22 +X 22 + X Haploid 22 +X 22 +Y n = 23 22 chromosomes + one sex Chromosome pairs ID size and shape, EXCEPT for sex X and Y determine gender in a 1:1 ratio Organism with 2 pairs of autosomal chromosomes + one pair sex One of each chromosome 3 chromosomes 1 complete set sex N=3 #1 #2 3 pairs 6 chromosomes 2 complete sets 2N = 6 X and Y chromosomes Sex Determination Humans vs Drosophila Sex In humans, presence of Y chromosome determines maleness: in In Drosophila, it does not - rather, sex is determined by ratio of X Drosophila it chromosomes to autosomes chromosomes e.g. XX e.g. XX X x 2:autosomes x 2 = normal female XY XY X x 1: autosomes x 2 = male 1: ...
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This note was uploaded on 10/04/2011 for the course BIOL 139 taught by Professor Christinedupont during the Spring '10 term at Waterloo.

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