The Work of Gregor Mendel 1822-1884

Gregor Mendel 1st person to trace successive generations of living things Augustinian Monk – Brunn, Austria taught natural science in high school “How did plants obtain atypical characteristics?”

Vocabulary Used in Genetics phenotype: physical expression of a gene genotype: a make of genes in a chromosome Tall = T short = t T T t t homozygous: alleles for a trait are the same T T heterozygous: alleles for a trait are opposite Tall Short T t

More Vocabulary Used in Genetics heredity: passing characteristics from parents to offspring genetics: study of heredity traits: inherited characteristics

More Vocabulary Used in Genetics gametes: sex cells (sperm and egg) fertilization: uniting of male and female gametes pollinization: plant fertilization zygote: cell produced by fertilization parent generation: P filial = son or daughter: F allele: factor that controls expression of a trait

Mendel’s Findings: Hereditary factors do not combine, but are passed intact to offspring. Each member of the parental generation transmits only half of its hereditary factors to each offspring. Certain factors are "dominant" over others. Different offspring of the same parents receive different sets of hereditary factors. Mendel's work became, and still is, the foundation for modern genetics.

Mendel's work became, and still is, the foundation for modern genetics. However------- Mendel's work became, and still is, the foundation for modern genetics.

Gregor Mendel and the Laws of Genetics I. Why Mendel succeeded: A. used controlled experiments B. studied only one trait at a time C. did mathematical analysis of data

II. Mendel’s Monohybrid Crosses A. First Generation Cross 1. tall pea plants = P1 2. short pea plants = P1 3. all offspring were tall = F1

B. Second Generation Cross 1. 2 tall offspring from first generation cross = F1 2. ¾ of these offspring = Tall = F2 3. ¼ of these offspring = Short = F2

C. Mendel’s conclusions: Rules 1. Rule of Unit Factors Each organism has 2 factors for each of its traits (alleles: gene alternatives) 2. Rule of Dominance For each trait there exists 2 possible factors that are expressed in physical characters, one that may be dominant, and the other recessive. 3. Law of Segregation The two alleles for each trait must separate when gametes form.

D. Expression of Traits 1. phenotype: physical expression of a gene 2. genotype: a make of genes on a chromosome 3. homozygous: alleles for a trait are the same 4. heterozygous: alleles for a trait are opposite

III. Reginald Punnett and the Punnett Squares A. English Biologist 1905: devised a shorthand way of finding the expected proportions of possible genotypes in the offspring of a cross C. Method called: Punnett Square Takes into account that fertilization occurs randomly 2. Agrees with Mendel’s law of segregation If you know the genotype of the parents, you can use a Punnett square to predict the possible genotypes of their offspring.

Punnett Square Reginald Punnett 1905

♂ T T t T t T t ♀ t T t T t V. Monohybrid Crosses

(cross involving two different traits) IV. Mendel’s Dihybrid Crosses (cross involving two different traits) A. experimenting with plants that had two different traits that differed from each other 1. used true-breeding pea plants that had round yellow seeds (RRYY) 2. crossed with true-breeding pea plants that had wrinkled green seeds (rryy) 3. smooth was dominant and wrinkled was recessive 4. yellow was dominant and green was recessive

true-breeding pea plants that had round yellow seeds round seeds yellow seeds RR YY RRYY

true-breeding pea plants that had wrinkled green seeds (rryy) wrinkled seeds green seeds rr yy rryy

true-breeding pea plants that had round yellow seeds wrinkled green seeds + RRYY + (rryy) RRYYrryy or RRrrYYrr

P1 R Y R Y R Y R Y R r Y y R r Y y r y R r Y y R r Y y R r Y y R r Y y

Result was 100% round yellow seeded plants true-breeding pea plants that had round yellow seeds true-breeding pea plants that had wrinkled green seeds + RRYY + (rryy) Result was 100% round yellow seeded plants

Offspring of P1 cross pea plants that had round yellow seeds wrinkled green seeds + RrYy (RrYy) + ? Result was different.

F1 R Y R y r Y r y R R Y Y r R Y Y R Y R R y Y r R y Y R R Y y r R Y y

Ratio = 9:3:3:1 9 round yellow RRYY 1/16 RrYy 4/16 9/16 RRYy 2/16 RrYY 3 round green Ratio = 9:3:3:1 RRyy 1/16 3/16 Rryy 2/16 3 wrinkled yellow rrYY 1/16 3/16 rrYy 2/16 1 wrinkled green rryy 1/16 1/16 16/16

Genes for different traits are inherited independently of each other. B. F1 generation produced all round yellow seeds C. F2 generation produced 9 round yellow 3 round green 3 wrinkled yellow 1 wrinkled green D. The Law of Independent Assortment Genes for different traits are inherited independently of each other.

Haploid n

Diploid 2n

S-phase of cell cycle 2n x 2

Meiosis I 2n x 2 2n 2n B A

n A 2n n Meiosis II

2n B n n

Dominant Examples Double Recessive Examples Examples Brown Eyes over Blue Eyes Color Vision over Color Blindness Hairy Heads over Bald Heads Curly Tongue over Flat Tongue Extra Fingers over Five Fingers Double Recessive Examples Examples Hemophilia Sickle-Cell Disease Tay-Sachs Disease Dwarfism

V. Probability

VI. Genetic Variation

VII. Crossing Over

Normal distribution of chromosomes during meiosis. VIII. NONDISJUNCTION 46 23 23 Normal distribution of chromosomes during meiosis.

NONDISJUNCTION 46 24 22

Trisomy(21) Down Syndrome Trisomy(13) Patau’s Syndrome Monosomy: Turner Syndrome Hexapoid: Wheat Triploid: Apples Polyploid: chrysanthamums