1 - BIO 320: Lecture 1 Mendelian inheritance: Segregation...

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Unformatted text preview: BIO 320: Lecture 1 Mendelian inheritance: Segregation & independent assortment 2008 Chapter 2: 2-5, 2-6, 2-8, 2-10, 2-13, 2-16, 2-18, 2-21, 2-25 QB: B1-20 Genetics: The study of variation and its inheritance Genotype: An organism's genetic composition or make-up (The human genome is known to contain about 30,000 genes). Phenotype: An organism's appearance (This is a function of the organism's genotype and its environment. For sanity's sake geneticists work with traits that are primarily under the control of genotype). Gene: Fundamental unit of inheritance (Note: Mendelian genetics was established without knowledge of the physical basis of genes and their mode of inheritance, i.e. it was an abstract conceptual framework). Mendel and his peas Trait Stem length Flower color Flower position Pod shape Pod color Seed shape Seed color Phenotypes Tall vs dwarf Purple vs. white Axial vs. terminal Inflated vs. pinched Green vs. yellow Round vs. wrinkled Yellow vs. green Allele: An alternative form of a gene. Terms used to describe alleles: Dominant: Recessive: A dominant allele produces a phenotype in the heterozygous condition. Recessive alleles produce phenotypes only in homozygous genotypes. MONO-HYBRID CROSSES & SEGREGATION Generation Parent (P) Observation Tall X dwarf (hybrid cross ) Interpretation TT X tt Genotypic ratio Filial 1 (F1) Tall (self cross of F1 progeny ) Tt F2 Tall & dwarf (3:1) ratio TT : Tt : tt (1:2:1) 3:1 Phenotypic ratio Terms used to describe genotypes: Homozygous: In an ind ivi dual homozygous for a particular gene, (a homozygote) all copies of that gene contain the same allele. For example, the TT, and tt genotypes in monohybrid cross shown above. Heterozygous: Heterozygotes carry different alleles of a gene. For example, the Tt genotype in monohybrid cross shown above. The Test Cross: Experimental determination of genotype for plants with dominant phenotype (e.g., F1 progeny of mono-hybrid cross) the Test Cross: If test generation individual was a TT homozygote, then all test cross progeny will be Tall (Tt) If test generation individual was aTt heterozygote, then test cross progeny will be Tall (Tt) dwarf (tt) in a 1:1 ratio T? X tt DI-HYBRID CROSSES & INDEPENDENT ASSORTMENT P: TT pp X tt PP F1: Tt Pp F2: Tall Purple: dwarf Purple: Tall white: dwarf white 3 ttP3 T-pp 1 ttpp 9 T-PTTPP x1 TtPP x2 TtPp x4 TTPp x2 ttPp x2 ttPP x1 Ttpp x2 TTpp x1 ttpp x1 Methods for determining Mendelian ratios: 1) PUNNETT'S SQUARE: (consider potential F1 gametes) TP TP Tp TTPP Tp TTPp tP TtPP tp TtPp parental gametes e.g. for Tt Pp x Tt Pp: 9 Tall, Purple 3 Tall, white 3 dwarf, Purple 1 dwarf, white tP tp ttpp 2) FORKED LINE METHOD: (Consider each trait individually) Tall vs dwarf (T,t) e.g. for Tri-hybrid cross Tt Pp Aa x Tt Pp Aa 3 Tall 1 dwarf Purple vs white (P,p) 3 Purple 1 white 3 Purple 1 white Axial vs terminal (A,a) 3 Axial 1 terminal 3 Axial 1 terminal 3 Axial 1 terminal 3 Axial 1 terminal = 27 Tall, Purple, Axial = 9 Tall, Purple, terminal = 9 Tall, white, Axial = 3 Tall, white, terminal = 9 dwarf, Purple, Axial = 3 dwarf, Purple, terminal = 3 dwarf, white, Axial = 1 dwarf, white, terminal ___ 64 Questions for thought: Are Mendelian ratios always observed? Why not? ...
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This note was uploaded on 06/03/2008 for the course BIO 320 taught by Professor N/a during the Spring '08 term at SUNY Stony Brook.

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