Mendelian Genetics How pea plants and humans mix it up

Early Ideas About Heredity People learned that it took two parents to make a baby People learned that it took two parents to make a baby Many early beliefs about how characteristics are transmitted. Many early beliefs about how characteristics are transmitted. Blending theory Blending theory

Early Research Mendel was not the first to perform experiments with pea plants Mendel was not the first to perform experiments with pea plants British farmers (stem height) British farmers (stem height) Performed almost the same experiments Performed almost the same experiments Obtained the same results Obtained the same results Over 200 years before Over 200 years before T A Knight (flower color) T A Knight (flower color) Same experiments Same experiments Same results Same results 1790’s 1790’s

Gregor Mendel Gregor Mendel Born in 1822 in the Chech republic Born in 1822 in the Chech republic Joined an Augustinian order in 1843 Joined an Augustinian order in 1843 Flunked out of college, but made some great friends who showed him the value of good data Flunked out of college, but made some great friends who showed him the value of good data Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

The Garden Pea Plant Self-pollinating Self-pollinating True breeding (different alleles not normally introduced) True breeding (different alleles not normally introduced) Can be experimentally cross- pollinated Can be experimentally cross- pollinated

F 1 Results of One Monohybrid Cross F 1 Results of One Monohybrid Cross

F 2 Results of Monohybrid Cross

Mendel’s Monohybrid Cross Results 787 tall277 dwarf 651 long stem207 at tip 705 purple224 white 152 yellow428 green 299 wrinkled882 inflated 6,022 yellow2,001 green 5,474 round1,850 wrinkled F 2 plants showed dominant-to- recessive ratio that averaged 3:1

Mendel’s Theory of Segregation Mendel’s Theory of Segregation An individual inherits a unit of information (allele) about a characteristic from each parent An individual inherits a unit of information (allele) about a characteristic from each parent During gamete formation, the alleles segregate from each other During gamete formation, the alleles segregate from each other

Now we know about Alleles, alternative forms of a gene

Punnett Square of a Monohybrid Cross Female gametes Male gametes A a A a AAAa aa Dominant phenotype can arise 3 ways, recessive only one

Test Cross Individual that shows dominant phenotype is crossed with individual with recessive phenotype Individual that shows dominant phenotype is crossed with individual with recessive phenotype Examining offspring allows you to determine the genotype of the dominant individual Examining offspring allows you to determine the genotype of the dominant individual

Punnett Squares of Test Crosses Homozygous recessive a A aaa Aa aa Homozygous recessive a A AAa Two phenotypesAll dominant phenotype

A Dihybrid Cross - F 1 Results AABBaabbx AaBb AB ab TRUE- BREEDING PARENTS: GAMETES : F 1 HYBRID OFFSPRING: purple flowers, tall white flowers, dwarf All purple-flowered, tall

16 Allele Combinations in F 2 aBaB AB abAbAb AbAb aBaB 1/4 AaBbAaBbaabbAabbaaBb AABBAABbAaBBAaBb AABbAAbbAaBbAaBbAabb AaBbAaBbaaBBaaBbAaBB 1/16

Explanation of Mendel’s Dihybrid Results If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible aBaB AB abAbAb AbAb aBaB 1/4 AaBbAaBbaabbAabbaaBb AABBAABbAaBBAaBb AABbAAbbAaBbAaBbAabb AaBbAaBbaaBBaaBbAaBB 1/16

Phenotypic Ratios in F 2 Four Phenotypes: Tall, purple-flowered (9/16) Tall, purple-flowered (9/16) Tall, white-flowered (3/16) Tall, white-flowered (3/16) Dwarf, purple-flowered (3/16) Dwarf, purple-flowered (3/16) Dwarf, white-flowered (1/16) Dwarf, white-flowered (1/16) AaBb X AaBbAaBb

Independent Assortment Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis