Ch_3_Wood_Mendelian_Basics-2

Ch_3_Wood_Mendelian_Basics-2 - MendelianGenetics Mendel...

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Mendelian Genetics Mendel examined discrete traits – Principle of Segregation
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Loci, genes, and alleles Locus (plural: loci) - Specific place on a chromosome Can be a gene or a non-coding region e.g. Xp13.3 Gene - A region of DNA that helps determine a characteristic e.g. β -globin gene, CFTR gene Allele - Two or more alternative forms of a gene e.g. A→T at β -globin causes sickle cell disease In everyday language, we might talk about a “gene for cystic fibrosis” Actually, all people have the gene : some individuals have a disease allele
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Genotype the genetic makeup of an individual can refer to the alleles (base pairs) at a particular locus OR an organism’s entire genetic makeup Phenotype (or trait) the physical characteristics of an organism is an expression of genotypes includes the way an organism looks or the proteins that are expressed Genotype  vs.  Phenotype
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Homozygote  vs.  Heterozygote Homozygote 2 alleles (or nucleotides) are same e.g. TT, tt (or GG, AA, TT, CC) Heterozygote 2 alleles are different e.g. Tt
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Dominant  vs.  Recessive Recessive not expressed in heterozygotes (the ‘little’ t in Tt) must occur in the homozygous recessive form (tt) to be seen Dominant expressed regardless of the other allele (TT or Tt)
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Mutant an allele that differs from the normal or most common allele, altering the phenotype Wild-type the most common phenotype in a population for a given gene often denoted with a ‘+’ Mutant  vs.  Wildtype
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Mendel’s Principles 1 st Principle: Segregation Suggested that traits were controlled by discrete units, which occurred in pairs These discrete units are now called alleles 2 nd Principle: Independent Assortment The distribution of one pair of alleles into gametes does not influence the distribution of another pair The genes (and their alleles) controlling different traits are inherited independently of one another
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Monohybrid Cross One locus, two alleles Gametes have only one allele 1st cross = P (parental) offspring of 1 st cross (P x P)=F1 offspring of 2 nd cross (F1 x F1)=F2 Pure-breeding P tall x P short gives all tall plants in the F1 generation F1 x F1 gives ¾ tall and ¼ short in the ratio of 3:1 Principle of segregation
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3.18 In sheep, lustrous fleece results from an allele (L) that is dominant over an allele (l) for normal fleece. An ewe (adult female) with lustrous fleece is mated with a ram (adult male) with normal fleece. The ewe gives birth to a single lamb with normal fleece. Is it possible to determine the genotypes of the parents? If so, what are they? If not, why?
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Crosses Self-fertilization – an individual is crossed with itself Intercross – cross between two heterozygotes Backcross - cross between F1 genotype and either of the parental (P) genotypes Reciprocal cross – crosses in which the phenotype of the
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This note was uploaded on 01/30/2010 for the course ECOL 320 taught by Professor Weinert during the Spring '07 term at University of Arizona- Tucson.

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Ch_3_Wood_Mendelian_Basics-2 - MendelianGenetics Mendel...

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