03-ch9-Mendel2 - Review • Is this pea homozygous or...

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Unformatted text preview: Review • Is this pea homozygous or heterozygous for color? • How would you discover which is true? test cross • Unknown is crossed with homozygous recessive: • What are the expected outcomes for F1 phenotype ratio? Yy x yy ... What is the expected offspring phenotype ratio? yy What is the expected offspring genotype ratio for this cross? y Y y y recall the dihibrid cross... law of segregation – the two alleles for a given gene separate during gamete production, so each gamete receives only one copy law of independent assortment – characters segregate of independent assortment segregate independently during the formation of gametes Mendel observed this for the traits he quantified... thi th Is it always true? • characters associated with alleles on different chromosomes chromosomes segregate independently independently law of independent assortment (recall meiosis...) SSss SSss YYyy yyYY SS SS ss YY SY ss yy yy YY SY sy sy Sy Sy sY sY a (recessive) genetic form of deafness in a human pedigree Joshua's phenotype? genotype? Abigail Linnel's phenotype? phenotype? Elizabeth's phenotype? genotype? genotype? Abigail Lambert's phenotype? genotype? Jonathan's phenotype? genotype? probability calculations • if an event is certain, probability is 1 P=1 • If an event cannot happen, probability is 0 P=0 • All other events have probability between 0 and 1. 0<P<1 2 independent events happening together • coin toss: P(heads) = 1/2 • joint probability of penny and dime toss = both heads? probability of penny and toss both heads • 1/2 of 1/2 • 1/2 x 1/2 = 1/4 or 0.5 x 0.5 = 0.25 event that can occur in 2 or more ways • gender of infant: P(boy) = 1/2 • probability of having 2 boys & 2 girls? of having boys girls? • this outcome can happen in the following ways: boy boy boy girl girl girl boy girl girl girl boy boy girl boy girl boy girl boy girl girl boy boy boy girl Probability (offspring = homozygous dominant)? P(S and S) 1/2 x 1/2 = 1/4 Probability (offspring = heterozygous)? P(S and s) or (s and S) (1/2 x 1/2) + (1/2 x 1/2) = 1/2 Probability (offspring = dominant phenotype)? P(SS) + P(Ss) + P(sS) (1/2 x 1/2) 1/2) + (1/2 x 1/2) + (1/2 x 1/2) 3/4 incomplete dominance – neither allele is dominant does this support the blending hypothesis? incomplete dominance sickle cell anemia RR – red blood cells are normal rr – red blood cells are so deformed they cannot carry enough O2 (lethal disease) Rr – red blood cells can carry O2 but not malarial parasite (this confers not malarial parasite (this confers resistance to malaria in Africa) “heterozygote advantage” Sickle cell allele frequency follows the geographical distribution of malaria http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html pleiotropy – single allele affects multiple phenotypes pleiotropy same allele causes Siamese color pattern & crossed eyes Si codominance – two alleles produce phenotypes that are both expressed at once how many phenotypes? how many genotypes? Many genes have more than two alleles in the population polygenic inheritance – some characters are determined by many alleles linked genes – alleles carried on the same chromosome tend to be inherited together (do not segregate during meiosis) exception: crossing over (during prophase I of meiosis) can cause recombinant phenotypes linked genes example, Drosophila alleles for body color & wing type are located on the same chromosome usually inherited together (parental phenotype) except when crossing over occurs (recombinant phenotype) genetic map shows relative position of genes on chromosome sex determination sex chromosome sex chromosome – chromosome (pair) that (pair) that determines the sex of an organism Parent can only give what they have to their gametes; male always is the donor of male always is the donor of a Y chromosome... chromosome but he could just as easily give an X instead sex of the (human) offspring is always determined of the (human) offspring is always determined by the father autosome – all other chromosomes sex-linked traits genes that determine sex are located on sex chromosomes genes that determine sex are located on sex chromosomes (but other genes are, too) hemizygous – having only one allele (as in the male XY) white eye mutation in Drosophila (recessive to wild type) Describe the (eye color) phenotype of this male Describe the phenotype of this female of this female X Y X X Phenotype of daughters? Phenotype of sons? or X Can females ever be white eyed? Y X X hemophilia: a sex-linked (recessive) genetic disorder in humans X Y who has the disorder? X X who can pass it on to sons? who can pass it on to daughters? review summary: non-mendelian heredity Environment influences gene expression point restriction pattern – enzyme produces pigment only at low temperatures (body extremities) epigenetics – (study of) the effects of environmental factors on gene expression http://www.pbs.org/wgbh/nova/sciencenow/3411/02.html ...
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This note was uploaded on 12/07/2011 for the course BIO 2 taught by Professor Poenie during the Fall '08 term at University of Texas at Austin.

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