Why Do You Look Like You Do? Genetics Why Do You Look Like You Do?

What You Should Learn From This Presentation You should know the definition of each of the bold, underlined words You should know the general theme of the presentation We will go over the presentation as a group, be prepared to discuss it

Genetics Defined as the study of heredity.

History of Genetics 10,000 years ago, farmers in Egypt bred wheat 4,000 years ago, Asian horse breeders kept records of animal traits Humans have been controlling the traits of crops and livestock since before the beginning of history

Gregor Mendel 1822-1884 Lived in Austria (now part of Czechoslovakia) Was an Augustinian monk Conducted breeding experiments in the monastery garden from 1856-1864 Published in 1866 (just after Darwin was published) No one cared until 35 years later (about 1900)

Gregor Mendel Experiment consisted of keeping amazingly accurate records of the garden pea He chose the pea plant because he could get pure strains that had been produced over years by gardeners The strains had many different varieties with contrasting traits He planted and kept records of over 30,000 plants

Gregor Mendel’s Results Trait First Generation (F1) Second Generation (F2) Ratio Yellow vs. Green Peas All yellow 6022 Yellow 2001 Green ? Round vs. Wrinkled Peas All round 5474 Round 1850 Wrinkled Inflated vs. Constricted Pods All Inflated 882 Inflated 299 Constricted Long vs. Short Stems All Long 787 Long Stems 277 Short Stems Colored vs. White Flowers All Colored 705 Colored 224 White Axial vs. Terminal Flowers All Axial 651 Axial 207 Terminal Green vs. Yellow Pods All Green 428 Green 224 Yellow

Gregor Mendel’s Results Did you see a trend? What is the final F2 ratio for each of the traits?

Gregor Mendel’s Results If you didn’t, go back and take a look again Notice that the trait in the F1 generation is always the larger number in the F2 generation

Gregor Mendel’s Results If you figured out the F2 ratio, you should have noticed something else Almost all of them are close to 3:1

Gregor Mendel’s Results Trait First Generation (F1) Second Generation (F2) Ratio Yellow vs. Green Peas All yellow 6022 Yellow 2001 Green 3.01:1 Round vs. Wrinkled Peas All round 5474 Round 1850 Wrinkled 2.96:1 Inflated vs. Constricted Pods All Inflated 882 Inflated 299 Constricted 2.95:1 Long vs. Short Stems All Long 787 Long Stems 277 Short Stems 2.84:1 Colored vs. White Flowers All Colored 705 Colored 224 White 3.15:1 Axial vs. Terminal Flowers All Axial 651 Axial 207 Terminal 3.14:1 Green vs. Yellow Pods All Green 428 Green 224 Yellow 2.82:1

Gregor Mendel’s Results Why did all of the F2 generations have a three to one ratio when the F1 generation were all one trait? Because the pure parents each gave a gene or “factor” to each of the F1 offspring and one of those genes were dominant over the recessive gene

Gregor Mendel’s Results Yet, some of those F1 generations passed on the the genes to their F2 generations

Gregor Mendel’s Results The F2 generation must have had some of the traits from the P1 generation, but we were unable to see the recessive traits. They were masked or covered by the dominant trait.

Mendel’s First Principle Principle of Dominance and Recessivness Each trait is controlled by a pair of factors (chromosomes) The dominant factor masks or hides the recessive factor

Genotype vs. Phenotype Genotype describes the genetic make-up of the organism The actual genes Phenotype describes the physical make-up of the organism What traits does the organism show

Mendel’s Second Principle The Principle of Segregation Heredity factors are determined by distinct factors For each trait, an individual carries two factors for each trait The two factors of each trait segregate and end up in separate gametes

Mendel’s Second Principle Today, those factors are called genes Part of the DNA Each gene codes for one trait Those are called alleles

Mendel’s Second Principle If you did the cross below, what is the probabilty of each genotype?

Monohybrid Cross Tt x Tt T t TT Tt tt

Monohybrid Punnett Squares Now you try some: Tt x tt Tt x TT TT x tt