Lecture 7-Meiosis and Mendel

Lecture 7-Meiosis and Mendel - flower colour Statistical...

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Lecture 7- Meiosis and Mendel Nuclear Proteins Keratin Helicase Histone Ligase Homologous Chromosomes -Same size and shape, one from each parent; different versions of the same gene -Same banding pattern -Will pair up in a Kareotype (genes are not visible, too condensed) -Pair and cross over during prophase I Reductional Division: Meiosis I -Number of chromosomes cut in half Equational Division: Meiosis II -Number of chromosomes does not change Mendel -Working only 150 years ago; brought scientific approach to the study of heredity -Studied several different discrete characteristics in the garden pea -Carefully controlled pollinations and quantitative analysis of several generations -Made “models” to explain observations Careful Experiments -Pollen from one plant is brushed onto the stigma of a second plant so that it cannot self- fertilize -The cross-fertilized plant produces seeds, which may be scored for seed traits, such as smooth or wrinkled shape, or may be grown into plants for scoring of adult traits, such as
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Unformatted text preview: flower colour Statistical Observations Character Traits crossed F1 F2 Ratio Seed shape Round x wrinkled All round 5474 round 1850 wrinkled 2.96:1 Seed colour Yellow x green All yellow 6022 yellow 2001 green 3.01:1 Pod shape Inflated x constricted All inflated 882 inflated 299 constricted 2.95:1 Pod colour Green x yellow All green 428 green 152 yellow 2.82:1 There was generally a 3:1 ratio among the phenotypes, and a 1:2:1 ratio of genotypes Explanatory Model-Variation in traits due to different alleles-Organisms inherit two alleles for each trait-Dominant alleles determine the appearance of heterozygotes-Alleles segregate randomly into gametes Probability -The randomness inherent in chromosome segregation at meiosis allows probability theory to predict the outcome of crosses -A dihybrid cross of two genes with two alleles each will give a 9:3:3:1 ratio overall...
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