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Monday, February 25, 2013

Monday, February 25, 2013. Take a penny lab and staple it Take a “ How to Solve a Basic…. ” handout Turn in Meiosis Lab onto Computer cart. Genotype Phenotype Homozygous Heterozygous Allele. Gregor Mendel : ‘ father ’ of modern genetics.

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Monday, February 25, 2013

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  1. Monday, February 25, 2013 • Take a penny lab and staple it • Take a “How to Solve a Basic….” handout • Turn in Meiosis Lab onto Computer cart

  2. Genotype • Phenotype • Homozygous • Heterozygous • Allele

  3. Gregor Mendel: ‘father’ of modern genetics • Why did Mendel use pea plants for his experiments? • Easy access and availability • Plants Exist in many varieties; have > heritable traits • Able to control reproduction of peas: self vs. cross pollination • Choose characters (traits) that exist in 2 distinct forms • Start experiments with true (pure) breeding [homozygous] lines of plants for a character/trait • Document parental cross & results of ALL offspring • Able to perform lots of trials in short time; obtain >> offspring

  4. Mendel’s Results and Conclusions (laws) • There are alternate versions of a trait (gene) = allele • Alleles are at the same locus on homologous Chromosomes • Offspring receive 2 alleles of each trait: one from each parent • Homologous Chromosomes ‘re-pair’ when gametes combine to form zygotes • Each allele (on homologous Xome) separates during gamete formation: Law of Segregation (Law of meiosis)

  5. If alleles for a trait are different (Rr) then 50% chance of gametes (1/2) receive one allele (R) & 50% receive the other allele (r) • If alleles are different: Rr, then one allele ‘R’ is fully expressed as phenotype & other allele ‘r’ has no phenotypic effect =Law of Dominance

  6. Law of Independent Assortment • If two or more traits are present in a genotype: AaBbDdEE it can be assumed (unless otherwise stated) that each allele (letter) is on a separate chromosome -->So how many chromosomes are represented by the genotype above? -->How many possible gametes are created from the genotype above? (HINT: each trait is on a separate chromosome so apply law of independent assortment!) --> How many possible offspring genotypes exist if both parents have the genotype above?

  7. Mendel and Genetics Problem Vocabulary • Generations: P1, F1, P2, F2 • Gene, Allele, Trait • Dominant allele, recessive allele • Homozygous, Heterozygous • Genotype, Phenotype • Genotypic Ratio, Phenotypic Ratio • Test Cross • Hybrids: Monohybrid, Dihybrid, Trihybrid

  8. Mendel and Genetics Problem Vocabulary Trait = Seed shape Phenotypes: Round seeds or Wrinkled seeds Genotypes: = AA, Aa, aa Homozygous = AA or aa Homozygous Dominant = AA Homozygous Recessive = aa Heterozygous (hybrid) = Aa Genotypic Ratio: 1AA : 2 Aa : 1aa Phenotypic Ratio: 3 Round : 1 Wrinkled

  9. Probability Rules Probability = chance event will occur total # of possible events “AND” Rule: Rule of Multiplication For two or more separate events occurring at the same time (or in succession), multiply the individual probabilities of events together EX 1: If parents are BB and Bb, what is chance of B gamete & b gamete combining to form zygote? 1/1 B and 1/2 b = 1/1 * 1/2 = 1/2 chance of Bb zygote EX 2: Parent genotype is AaBBDdEe: What is probability of gamete with genotype of ABdE? 1/2 * 1* 1/2 * 1/2 = 1/8 chance of ABdE

  10. OR T + t + t T 1 4 1 4 + = Probability Rules “OR” Rule: Rule of Addition To determine the chance one event OR another will occur, ADD the individual probabilities of each event EX 1: If both parents are Tt, what is chance offspring will also be Tt? 2 4

  11. Pedigrees (family tree)p. 260 & fig 14.14 A pedigree is a family history showing inheritance of a particular trait through familial generations

  12. Karyotypes (figure 13.3, p. 237) Karyotypes are photographs of stained, human chromosomes present at metaphase of mitosis. Karyotypes are used to determine if chromosomes are defective and help to diagnose chromosomal disorders such as Down’s Syndrome.

  13. Karyotype of Normal Female

  14. Karyotype of Down’s Syndrome Individual Down’s Syndrome is also called Trisomy 21. Is this a boy or girl’s karyotype?

  15. Non-disjunction of either homologous chromosomes during meiosis I How does trisomy occur? Non-disjunction of sister chromatids during meiosis II

  16. Some gametes exhibit trisomy (n+1) while others exhibit monosomy (n-1)?

  17. Some gametes exhibit trisomy (n+1) while others exhibit monosomy (n-1)?

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