2011 Slide Set VIII&IX

2011 Slide Set VIII&IX - UNIT II: SLIDE SET VIII I....

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UNIT II: SLIDE SET VIII I. Extensions of Mendel’s Rules (continued) E. Sex Linked Inheritance 1. Sex chromosomes 2. Systems of sex determination a. XY system b. X0 systems c. ZW systems d. Haplo-diploid systems e. Non-chromosomal sex determination 3. X-linked inheritance 4. Y-linked inheritance 5. Effects of sex on autosomal traits
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Exceptions to Mendel’s rules (cont’d): 4. Individuals have 2 versions (alleles) for each gene (i.e., alleles occur on homologous pairs of chr’somes) Exception: genes on the ________ chromosomes (= “ _________ ” genes: genes “linked” to or found on one of the sex chromosomes)
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Y chromosome (replicated) in humans and many other species, the composition of the sex chromosomes varies between males and females. females ______ , males _____ these X and Y chromosomes can have some same genes but the X and Y act like ___________ during meiosis because of “pseudoautosomal” regions (regions in common) Fig. 15.5 (7 th : p. 282) X chromosome (replicated)
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Human copyright © 1994 David Adler http://www.pathology.washington.edu/research/cytopages/idiograms/human/ http://www.pathology.washington.edu/galleries/Cytogallery/main.php?file=human%20karyotypes RECALL: human male and female karyotypes male female no “Y”
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humans: XX (female) x XY (male) male gametes: 1/2 X 1/2 Y female 1/1 X gametes (only X is possible) 1/2 XX 1/2 XY Therefore: in humans, gender of offspring is “determined” by __________ _______________ (sperm) Punnett square explains the ________ of males to females observed in the human population
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A closer look at the human Y-chromosome: ______ locus/gene = s ex-determining r egion on ___ * SRY gene is “activated”/expressed in an _________________ - gonad cells in embryo start to produce H-Y antigen on cell surfaces so the gonads develop into _______ (= so the embryo develops as a “male”). XX female embryos have no SRY gene, so no H-Y antigens are made - so embryonic gonads continue to develop into _______ (= “female”)
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Figure 7.19 Human Heredity, 4th edition, Michael R. Cummings Human gonad development depends on presence OR absence of the Y chromosome (& its SRY gene) Embryos are “sexually indifferent” up to 7 weeks; then if Y chromosome is present, the ____ gene is activated & gonads differentiate into ____ (left side of figure).
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Various Chromosomal Systems of Sex Determination in Animals Humans: males are “ ________ gametic ” (XY) females are “ _______ gametic ”(XX) Birds: males are “homogametic” (ZZ) females are “heterogametic” (ZW) Fig. 15.6 (7 th : 15.9) Grasshoppers: the numbe r of X chromosomes determines gender (i.e., no “Y”) Some flies (& some other insects): whether zygote was haploid or diploid determines gender…
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Haplo-diploid sex determination: - social insects (ants, bees) - no sex chr’somes involved - fertilized egg = ________ female - unfertilized egg = ________ male
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determination is also seen in
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2011 Slide Set VIII&IX - UNIT II: SLIDE SET VIII I....

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