Chapter 5: Heredity

1. Chapter 5: Heredity http://www.youtube.com/watch?v=6OPJnO9W_rQ

2. Chapter 5 – Heredity • An organism is a collection of traits, all inherited from its parents • Heredity: the passing on of characteristics (hair color, skin color, eye color, height, body shape… overall appearance inside and out) from one organism to its offspring • How are these characteristics passed on? • DNA – contains the ability to make and control every part of an organism • The different forms of a trait that make up a gene pair are called alleles. • When a pair of chromosomes separates during meiosis, alleles for each trait also separate into different sex cells. • Every sex cell has one allele for each trait

3. Genetics: the study of how traits are inherited through the interactions of alleles.

4. Discovery of DNA – 100 years ago by Gregor Mendel • Experimented with garden pea plants and could explain how traits were passed on from one generation to another. • Why pea plants? • Grew quickly, • Many generations could be seen in a short period of time, • Crossed and bred easily Why not use animals? • Multiple generations take too long

5. Mendel’s Experiments studied many different characteristics of pea plants • First Characteristic – Plant Height • Crossed Short X Short plants – Parental generation = P1 • This Produced all short plants – 1st generation = First Filial generation= F1 • Crossed seeds form those plants with each other • Produces all short plants – 2nd generation = Second Filial generation= F2 • Conclusion = All generations resembled parents • Called this = True Breeding Plants… we now call this Purebred

6. Crossed Tall X Tall plants – P1 • Some tall x tall crosses produces all tall plants – F1 • Some tall x tall crosses produced both tall and short plants – F1 • Conclusion = Two kinds of tall plants = True Breeders, and some were NOT True Breeders (Hybrids) • Crossed Tall X Short plants = P1 • Produced all Tall plants = F1 • Crossed F1 plants with its own pollen • Expected all Tall plants… But… • Produced some Tall plants and some Short plants in the F2 • Shortness had reappeared! • Plants did Not breed true • Conclusion = Plants had to contain factors for both tallness and shortness • Factors = Genes = unit of heredity

7. Mendel knew when you crossed a Tall plant with a Short plant, the next generation was Tall • The stronger Tall characteristic had covered the weaker short characteristic • This strong characteristic is called Dominant • The weaker trait that is covered or hidden is called Recessive • Today = the Dominant trait is symbolized by capital letters, the Recessive trait is symbolized by lower case letters • IE = Dominant = T • Recessive = t • (Explain crosses in form of dominant and recessive letters.) • (Show IE on board.)

8. From multiple experiments with many characteristics, Mendel created a hypothesis: • each pea plant had a pair of factors (Genes) • Also – each parent contributed only one of those factors to each plant in the next generation • One gene from each parent created the gene pair in the next generation

9. PunnettSquares: • chart that shows possible combinations of the cross between two organisms • Guinea pigs – color • Black crossed with White • Black = BB • White = bb • (Show on board) • Percentages Black? • Percentages White? • BB (2 capital Letters)= Homozygous Dominant – Purebred • bb (2 lower case letters)= Homozygous Recessive – Purebred • Bb (capital and lower case letters)= Heterozygous

10. Phenotype = Visible characteristics - looks like… • Genotype = Genetic makeup • genes look like… • Now cross two of F1 Generations from guinea Pigs… • Bb X Bb • (Show on board) • Percentages? • White? • Black? • Homogeneous Black? • Heterogeneous Black? • Homogeneous White? • Mendel’s work remained unnoticed until around 1900 • Scientists found his work… still gave him credit! • Led to Crick and Watson description of DNA.