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Mendelian Genetics

Mendelian Genetics. Gregor Mendel. carried out the first important studies of HEREDITY used pea plants which reproduce sexually by way of sex cells called gametes. Heredity. the passing on of characteristics from parents to offspring. Genetics. The branch of biology that studies heredity.

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Mendelian Genetics

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  1. Mendelian Genetics

  2. Gregor Mendel • carried out the first important studies of HEREDITY • used pea plants which reproduce sexually by way of sex cells called gametes

  3. Heredity • the passing on of characteristics from parents to offspring.

  4. Genetics • The branch of biology that studies heredity.

  5. Gametes • Male and female sex cells • The male sex cell is called a sperm • The female sex cell is called an egg

  6. Monohybrid Crosses • Mendel took tall plants and “crossed” them with short plants • the offspring were called HYBRIDS (parents had opposite traits—tall & short) • he noticed that all of the first generation offspring were TALL • he let those plants pollinate and produce over 1000 plants which he studied

  7. Second Generation • Of those 1000 plants that were produced by the hybrid tall plants… • ¾ of them were TALL • ¼ of them were short (how did that happen?) • Mendel did more tests on more traits and got the same results

  8. Mendel’s Conclusions • Each organism has 2 factors that control each of its traits. (we now know that these are genes located on chromosomes) • We call these different gene forms alleles • A plant could have 2 tall alleles or 2 short alleles or 1 of each • The 2 alleles are located on different chromosomes (one from ma--one from pa)

  9. The Rule of Dominance • Dominant trait • only need one allele of this type to exhibit the trait • represented by upper-case letter (written 1st) • Recessive trait • need 2 of these alleles to exhibit the trait • represented by lower-case letter

  10. LAW OF SEGREGATION Mendel’s 1st Law: • Each individual has 2 alleles which make 2 different gametes • remember meiosis?!? • During fertilization, male and female gametes randomly pair and 4 combinations of alleles are possible.

  11. INDEPENDENT ASSORTMENT Mendel’s 2nd Law: • genes are inherited independently of each other

  12. Punnett Squares • predict possible genotypes of one’s offspring (probability) • monohybrid cross: tests one trait • dihybrid cross: tests two traits

  13. Hetero or homo? • heterozygous = 2 different alleles (Bb) • homozygous = 2 like alleles (BB or bb) *these letters represent an organism’s genotype (the combination of genes in an organism)

  14. JUST DO IT! R = round r = wrinkled What type of offspring can be produced by a homozygous round (____) and a homozygous wrinkled (____)pea plant?

  15. RR x rr • this is called a monohybrid cross because we are looking at just one trait at a time R R r r

  16. RR x rr • 100% of the offspring will be heterozygous (Rr) • What will they look like (phenotype)? R R r r Rr Rr Rr Rr

  17. What is the probability of having a wrinkled pea plant if both parents are heterozygous? R r R r

  18. Wrinkled is a recessive trait, so offspring must be homozygous to be wrinkled (rr) Only 1 out of 4 offspring will be wrinkled = 25% probability R r R r RR Rr Rr rr

  19. A homozygous brown eyed male and a heterozygous female mate. What is the probability their child will have blue eyes? Let: B = brown b = blue B B B b

  20. All babies have brown eyes!0 % probability of a blue-eyed baby Let: B = brown b = blue B B B b BB BB Bb Bb

  21. Dihybrid CrossRRYY x RrYy two traits at a time! R = round r = wrinkled Y = yellow y = green

  22. What is the probability of producing a yellow and round plant?

  23. What is the probability of producing a yellow and round plant? RY RY RY RY RY Ry rY ry RR YY RR YY RR YY RR YY Yellow = YY or Yy Round = RR or Ry RR Yy RR Yy RR Yy RR Yy 16/16 or 100% Rr YY Rr YY Rr YY Rr YY Rr Yy Rr Yy Rr Yy Rr Yy

  24. Do Punnett Practice WS

  25. Pedigrees • track males and females with and without certain traits using symbols • also can track sex-linked traits female without trait male without trait female with trait male with trait

  26. Sex-linked traits • can be dominant (just one needed) or recessive • traits carried on the X chromosome • females are XX while males are _____ • Y chromosomes do not have genes so do not carry traits

  27. Pedigrees are like dihybrid crosses a female with blue eyes mates with a heterozygous male, what is the probability they will have a brown eyed girl?

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