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Patterns of Inheritance

Patterns of Inheritance. Genetics I. Old Theories. Extreme breeding could occur Giraffe (mix of camel & leopard) Homunculus All information from father Traits transmitted directly Body parts from parents i.e. bad limb Blending Mom (blond hair) & Dad (brown) Kid=blond-brown hair.

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Patterns of Inheritance

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  1. Patterns of Inheritance Genetics I

  2. Old Theories • Extreme breeding could occur • Giraffe (mix of camel & leopard) • Homunculus • All information from father • Traits transmitted directly • Body parts from parents • i.e. bad limb • Blending • Mom (blond hair) & Dad (brown) • Kid=blond-brown hair

  3. Who was Mendel? • Monk/Scientist… • “Father of Genetics” • Worked with peas… • Focused only on 7 traits • Controlled breeding • Self- & cross-fertilization • Recorded numerical data • Able to predict probabilities • Laws & theories still around today

  4. Why the Pea? 1.) Easy to grow 2.) Take little space 3.) Produce lots of offspring 4.) Quick generation time 5.) Traits easy to see 6.) Control breeding -Work with pure (true-breeding peas) -Easily manipulated (self & cross-fertilization)

  5. Terms to Know • Alleles-copies of a gene (diploid has 2) • Homozygous-same copy of gene (AA, aa) • Heterozygous-diff. copies of gene (Aa) • Genotype-Alleles an individual has • Phenotype-Physical appearance of genes • Dominant-trait is expressed (overrides) • Recessive-trait is not expressed (ex. aa) • Wildtype-most common allele of a gene • Mutant-less common allele of a gene

  6. Mendel’s Laws • 1) Law of Segregation: • During meiosis, chromosomes separate & each gamete randomly gets one copy of gene (or allele) • Genes (alleles) segregate & remain distinct

  7. Mendel’s Laws • 2) Law of Independent Assortment: • Genes located on different chromosomes separate independently during meiosis

  8. Quick Quiz #1 • Mendel is ‘the father of…’ • Genetics • Why the Pea Plant? • Aa is _____, AA is ______, & aa is _______. • Heterozygous, Homozygous dom, & Homozygous rec. • Genotype is ______, phenotype is _______. • Allele combinations an individual has, physical appearance • A ______ allele overrides a ______ allele. • Dominant, recessive • What were Mendel’s Laws & what did they mean? • Law of Segregation & Law of Independent Assortment

  9. Terms to Know • Parentals-Two organisms (with differing traits) used for studying inheritance • F1-First filial generation, offspring from two contrasting parents • a.k.a. hybrids • F2-Second filial generation, offspring from (hybrid) F1 generation

  10. Mendel Found (flower color) • Parentals were crossed (purple-PP & white-pp) • F1s all showed dominant trait (purple-Pp) • No white flowers & no blending • F2s showed… • 75% had dominant trait, purple flowers (PP or Pp) • 25% had recessive, white flowers (pp) • Still…no blending • Make it simple with Punnett Squares 

  11. P P p p Parentals- PP (purple) & pp (white) F1- all Pp (purple)

  12. P P p p F1s- Both Pp (purple) F2s- 3 purple : 1 white /1 PP : 2 Pp : 1 pp

  13. Testcross • How could Mendel tell if purple flower was PP or Pp? • Cross with pp • If all offspring were purple…PP • If ½ offspring were purple & ½ white…Pp

  14. Dihybrid Cross • Two traits (pg 252) • Color & Shape • Parentals are… • Round, yellow (RRYY) • Wrinkled, green (rryy) • F1s are all round, yellow (RrYy) • Gametes are combination • F2 phenotype=9:3:3:1 • Traits independent of each other • ¾ yellow, ¼ green • ¾ smooth, ¼ wrinkled

  15. Terms to Know • Linked genes: close enough on a chromosome that they won’t sort independently, move together in meiosis • Human Genome Project: mapping entire genome, learning gene locations • Accomplished in 2003, still making corrections

  16. Quick Quiz #2 • What did Mendel find when he crossed purple & white parentals? • All purple F1s (4:0) • What did Mendel find when he crossed the F1s? • 75% purple, 25% white (3:1) • What was the true genotypic ratio? • 1:2:1 • What’s the purpose of a test cross? • To find the original parental genotype • What did the dihybrid cross tell us? • Traits assort independently of eachother

  17. Weird Things About Inheritance Co-dominance Polygenes Pleiotrophic Environmental Effects Incomplete Dominance

  18. Incomplete dominance An intermediate of both parents, a mix

  19. Polygenetic– many genes affect 1 trait act jointly to influence a trait—eye color, weight, height… • Pleiotrophic—one gene affects many traits associated with disorders: Cystic fibrosis, sickle cell anemia, albinism • Multiple symptoms caused by one gene

  20. Environmental Effects • Heat-sensitive alleles (enzyme tryosinase production on melanin) • i.e. Arctic fox, hare, ptarmigan, Himalayan rabbits, Siamese cats • In humans: weight, height, health, etc.

  21. Continuous Variation • Gradual changes within a species • height , weight , foot length • E.g. Look at height

  22. Codominance-Blood Type • Multiple alleles: each allele has its own effect on the ‘big picture’ • Blood type (i.d. markers on blood cells…sugar) • Gene (I) has three alleles which add diff. sugars • IB—galactose • IA—galactosamine • i—does not add any sugar • Remember, you have two alleles so different combinations can occur

  23. Codominance-Blood Type • Type A—add only galactosamine • Either IAIA(homozygotes) or IAi (heterozygotes) • Type B—add only galactose • Either IBIB (homozygotes) or IBi (heterozygotes) • Type AB—add both sugars • IAIB (heterozygotes) • Type O—add neither sugar • ii (homozygotes)

  24. Quick Quiz #3—Matching • Codominance • Pleiotrophic • Continuous Variation • Polygenetic • Incomplete dominance • Environmental effects • Gradual changes within a species • Two dominant alleles combine and parent traits are mixed • Two dominant alleles combine, but the parent traits are not mixed (i.e. blood types) • Individual’s surroundings play a role in physical traits • Many genes, one trait • One gene affects many traits

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