BSCI 110B UNIT III OUTLINE

BSCI 110B UNIT III OUTLINE - BSCI 110B UNIT III OUTLINE...

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BSCI 110B UNIT III OUTLINE MENDELIAN GENETICS Mendel used scientific approach to identify two laws of inheritance The laws of probability govern Medelian inheritance The particulate hypothesis challenged the blending idea and said that parents pas on discrete heritable units (genes) Mendel used peas and tracked characters that varied in an either/or manner He also used “true breeding” plants Hybridization – crossing of two true breeding varieties P generation – parents F1 generation – offspring of P generation F2 generation – offspring of F1 generation Character is a heritable feature that varies among individuals Trait is a variant for a character Alternative versions of genes account for variations in inherited characters Alternative versions of a gene are called alleles For each character, an organism inherits two alleles, one from each parent If the two alleles at a locus differ, then one, the dominant allele determines the organism’s appearance; the other, the recessive allele , has no noticeable effect on the organisms appearance Law of segregation – two alleles for a heritable character segregate during gamete formation and end up in different gametes Law of independent assortment says that each pair of alleles segregates independently of each other pair of alleles during gamete formation Homozygotes have two identical alleles for a character and heterozygotes have two different alleles for a gene Alternative versions of genes = alleles Each gene resides at a specific locus on a specific chromosome Testcross breed with homozygous recessive individuals A dihybrid cross, a cross between F 1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently The law of independent assortment only applies to genes on different, nonhomologous chromosomes Genes located near each other on the same chromosome tend to be inherited together Incomplete Dominance: pink plants from red and white cross Codominance blood types Most genes have multiple phenotypic effects, a ptoperty called pleiotropy Sickle cell anemia affects one out of 400 African-Americans The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells Symptoms include physical weakness, pain, organ damage and paralysis
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Epistasis a gene at one locus alters the phenotypic expression of a gene at a second locus For example, in mice and many other mammals, coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles C for pigment color and c for no pigment color ) determines whether the pigment will be deposited in the hair Most genetic diseases are recessive Dominant alleles are more frequent in popultions than recessive alleles Most genes exist in populations in more than two allelic forms
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This note was uploaded on 11/12/2010 for the course BSCI BSCI 110B taught by Professor Johnson during the Spring '09 term at Vanderbilt.

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BSCI 110B UNIT III OUTLINE - BSCI 110B UNIT III OUTLINE...

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