Genetics!

1. Genetics!

2. The Blending Hypothesis • A Trait is a variation of a particular characteristic such as tall and short • In the early 1800’s many biologists believed in the Blending Hypothesis • They believed offspring were a blend of their parents traits • BLACK SQUIRRELL + WHITE SQIRRELL = GREY SQUIRRELL!!

3.  Gregor Mendel “Father of Genetics” Genetics – the study of heredity  Thomas Hunt Morgan. “Father of Modern Genetics”

4. The Father of Genetics- Gregor Mendel • Gregor Mendel (1822-1884) • Austrian Monk • Pea Plant Experiments • Mendel studied the inheritance of traits (factors) from one generation to the next • These factors are now called genes • Genes are sections of DNA that code for a specific trait or a characteristic

5. Mendel’s Breeding Experiments • Mendel bred plants for years to ensure that they were true-breeding • True-breedingmeans that offspring always had the same trait as the parent • MendelCross-fertilized all his pea plants by hand to control which traits he wanted to test

6. Mendel’s Breeding Experiments • Mendel expected a blending of the traits • IE: Tall pea x Short pea resulting in Medium height plants • What actually occurred:

7. Some Mendelian Conclusions: • Mendel and Alleles: • Mendel developed the hypothesis that genes came in different forms that he called Alleles • Tall vs. Short • Yellow vs. Green • We use letters to represent alleles • Tall = T • Short = t

8. Some Mendelian Conclusions: • Law of segregation • When gametes are made the alleles for a trait separate, so each gamete carries only one allele for each trait • Law of dominance: • “of the two factors controlling a trait, one may dominate the other”

9. Punnett Squares • Punnett Squares are tools used to determine offspring probabilities from a genetic cross

10. Punnett Squares • Genotype – the Allele combination of an individual (like their I.D. number) • Phenotype – the physical characteristic that the individual shows (tall, short, eye color, etc…)

11. Sample Problem • Let’s say you are Mendel. You take a pure-breeding pea plant that is tall (TT) and you combine it with a pure-breeding pea plant that is short (tt). What would their possible offspring be? • What would you do first? t t T Tt Tt T Tt Tt

12. Sample Problem • Let’s look a little more closely at the plants • Homozygous– An individual that has two copies of the same allele • Which of the plants in the sample are homozygous? • Heterozygous – An individual that has two different copies of an allele • Which of the plants in the sample are heterozygous? t t T T

13. Sample Problem • The offspring would look something like this • Why are all the offspring tall? • Dominant – an allele that “masked” or covers up another allele • Recessive – an allele that does not show up in a heterozygous individual, it is “masked”

14. Dominant Genes • If an individual is Homozygous Dominant the dominant gene will be seen • Example: TT = tall • If an individual is Heterozygous the dominant gene will be seen • Example: Tt = tall • If an individual is Homozygous Recessive the recessive gene will be seen • Example: tt = short

15. Some More Sample Problems As a Class: • Brown fur = B ; Grey fur = b • What is the genotype of a Heterozygous individual? • What is the genotype of a Homozygous dominant individual? • What phenotype would someone who is bb be (haha)? • Complete a Punnett square for Bb x BB Bb BB Grey fur B B B b

16. Key Terms • Genotype– Allele combination of an individual, two letters • Phenotype– Physical characteristics based on genotype (tall, brown hair, blue eyes, etc…) • Dominant– Covers up the other allele, will always be seen in the phenotype (UPPER CASE) • Recessive– Gets covered by the dominant, only seen if the individual is homozygous recessive (lower case) • Homozygous– Individual has two of the same allele (TT, bb, GG, hh) • Heterozygous– Individual has two different alleles (Tt, Bb, Gg, Hh)