Fundamentals of Genetics Mendel and Crosses Gregor Mendel

Fundamentals of Genetics Mendel and Crosses

Gregor Mendel • father of genetics • performed plant breeding experiments using garden pea plants

Garden Pea Plant

Who was this Mendel and what the heck is he doing in a monastery? • born in 1822 • trained himself to be a naturalist early in life • worked as a substitute science teacher • failed the qualifying exams to be a regular high school teacher! • joined a monastery in Brunn, Austria • sent to Vienna U. to study science and math

Why was Mendel successful? • used garden pea plant (readily available) • cultivated quickly • large number of offspring • only 7 traits • self-pollinating • logical experimental methods • kept very careful records

Self Pollination

Cross Pollination

TECHNIQUE 1 2 Parental generation (P) Stamens 3 Carpel 4

RESULTS First filial generation offspring (F 1) 5

Figure 14. 3 -3 EXPERIMENT P Generation (true-breeding parents) F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination F 2 Generation 705 purpleflowered plants 224 white flowered plants

Figure 14. 3 -3 EXPERIMENT P Generation (true-breeding parents) F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination F 2 Generation 705 purpleflowered plants 224 white flowered plants

Figure 14. 3 -3 EXPERIMENT P Generation (true-breeding parents) F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination F 2 Generation 705 purpleflowered plants 224 white flowered plants

1. Law of Unit Characters • a hereditary trait is carried by a pair of genes (Mendel’s factors) • one gene is on one chromosome and the other is on the other chromosome ex: TT, Tt, tt

2. The Principle of Dominance • dominant gene covers up (masks) the recessive gene if both are present • ex: plant color R-red (dominant) r- white (recessive) RR- red plant Rr- red plant rr- white plant

3. The Principle of Segregation • gene pairs separate into different gametes during meiosis • each gamete has only one gene from the pair ex: Tt separates into T and t Tt Meiosis T t Gametes

4. The Principle of Independent Assortment Parents Genotype • applies to gene pairs on different chromosomes • separation (segregation) of a gene pair is not affected by gene pairs on other chromosomes Yy Tt YT Possible Gametes • separate independently Yt yt y. T

S E S S O R C

Monohybrid Crosses • one pair of traits are considered in a cross • use a special chart called a Punnett square to predict the genotype of the offspring • phenotype ratio appearance • genotype ratio - genes in square

How to Work a Genetics Problem Follow these steps!

Read the problem. What information is provided in the problem? Cross a pure white flowered pea plant with a pure purple flowered plant. What is the trait? What is dominant? What letter will we Flower Color Dominant – purple - P Recessive – white - p use to represent this trait? What is recessive? What letter will we use to represent this trait?

Determine the genotypes of the parents. Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white Pure white X pp X Pure = homozygous Pure purple PP

Law of Segregation: Determine the gametes Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white Pure white pp X Pure purple X PP Meiosis p Gametes p P P Gametes

Punnett Square: place the gametes across the top and down one side Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white pp X PP p p P P P p

Punnett Square: join the gametes Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white pp X PP p p Pp Pp P P

Determine the genotype and phenotype of the offspring. Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white Genotype - Phenotype - pp X PP Pp P purple P p p Pp Pp purple

What is the genotype ratio? The phenotype ratio? Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white pp X PP Genotype Pp to PP or pp P p p Pp Pp 4: 0 Phenotype Purple to White 4: 0 P

What percentage of the offspring are homozygous? Heterozygous? Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white pp X PP Genotype Homozygous Heterozygous - P p p Pp Pp 0% 100% P

What percentage of the offspring are purple? White? Cross a pure white flowered pea plant with a pure purple flowered plant. P – purple p - white Phenotype Purple White - pp X PP P p p Pp Pp 100% 0% P

Cross 2 heterozygous purple flowered pea plants.