Gregor Mendel Father of genetics Mendel Successes 1

Gregor Mendel “Father of genetics”

Mendel Successes • 1 st to predict how traits are transferred from one generation to next • Successful b/c studied only one trait at a time to control variables & analyzed his data mathematically

Mendel’s experiments • Self-pollination true-breeding parent, only 1 plant • Cross-pollination (making a cross) offspring from two different parent plants

More on Mendel’s experiments • Mendel studied 7 traits on pea plants - Seed shape & color, pod color & shape, flower color, flower position, & plant height • Conducted monohybrid crosses looking at only 1 trait • Example – Flower color

What’s going on? • The white flower trait had reappeared. • Mendel repeated for other traits and in every case he found that one trait seemed to disappear in the 1 st generation only to reappear unchanged in ¼ of the 2 nd generation.

Mendel’s hypothesis 1. Organisms have 2 factors that described each trait alleles 2. Inherited one allele from father & other from mother

Explaining Mendel’s results • A purebred parent plant would have 2 identical alleles for purple flowers (PP) or 2 alleles for white flowers (pp) • F 1 offspring have 1 allele for purple flowers & 1 allele for white flowers (Pp) • F 2 offspring - pp, Some PP, Pp

Mendel’s Law of dominance • Some alleles are dominant (trait is expressed in the offspring) & other alleles are recessive (trait is only exhibited if dominant is absent) • Ex: Purple & white flowers

Law of segregation • Alleles for a trait will separate when the sex cells (gametes) are formed during meiosis. • Evidence – F 2 offspring show recessive trait.

Law of Independent Assortment • Genes for different traits are inherited independently from each other • Mendel discovered this through his experiments w/dihybrid crosses (2 parents w/2 different traits) • Ex: tall, yellow pea plant with a short, green pea plant

Environment affects gene expression • Internal - Age, gender (hormonal differences) – Ex: male bird feathers colorful • External - Temperature, nutrition, light, radiation, chemicals, viruses – Ex: leaves at top of trees

Review • Phenotype –What the organism looks like (physical appearance) –Ex: brown hair • Genotype –genetic makeup of an organism (we cannot see this) –Ex: Bb, BB

Two forms of Genotype • Homozygous –both identical alleles are either dominant or recessive. –Ex: BB or bb • Heterozygous –different alleles, one dominant & one recessive –Ex: Bb

Punnett Squares (PSq) • Developed in 1905 by Reginald Punnett. • Used to predict & compare possible genetic variations resulting from a cross • Probabilities, not exact results

Symbols used in PSq • Original parents P 1 generation • Offspring of the parent plants F 1 generation • Offspring of the F 1 generation F 2 generation

Example

Steps to solving PSq 1. Identify the dominant & recessive alleles 2. Write the genotypes of the parents 3. Determine the possible gametes the parents can produce (how the alleles will separate)

4. Enter the possible gametes at top (#1 parent) & side (#2 parent) of the PSq 5. Complete the PSq write the alleles from the gametes in the appropriate boxes 6. Determine the phenotypes of the offspring and percentages of each

PSq Practice • Heterozygous yellow seeds x homozygous green seeds Y • Key : – Y yellow seeds –y green seeds y y y

Answer Y y y Yy yy

Now try this sex-linked trait • Heterozygous normal female x normal male N h X X • Key : – X N normal X – X h hemophilia Y – Y normal N

Answer X X Y N X X N X Y N N h X X N X Y h h

Now try problems on: • Working with Punnett squares worksheet STOP click here

Dihybrid cross – like a puzzle • Can 2 parents with Heterozygous round, yellow seeds produce offspring with wrinkled, green seeds? • 1 st – determine possible gametes/ allele partners – – First Outside Inside Last • Set up PSq boxes

Practice Dihybrid Cross • Heterozygous Purple Flower & Homozygous Tall X Homozygous white flower & Heterozygous Tall Key: F purple flower T tall f white flower t short