History of Genetics

History of Genetics What is Genetics? • Record each kittens coat colors and patterns? • Record the mother’s coat color and pattern? What do you think the father looked like? What is your evidence. Gregor Mendel • In 1851, a monk from Europe became curious about some plants in his garden had different traits. • TRAITS: A characteristic that an organism can pass onto its offspring through its genes. • Mendel began studying pea plants Mendel’s Pea’s Mendel studies seven different traits in pea plants. Each trait has two different forms. His Discovery • Mendel discovered that the pea plants’ traits were often similar to the parents. • Sometimes the pea plants had different traits then their parents • Mendel tested thousands of pea plants to understand the process of heredity Heredity • Heredity is the passing of traits from parents to offspring What Does this Mean for Mendel and genetics? • Today, Mendel is considered the father of genetics. • GENETICS: The study of heredity What You Need to Know to Understand Mendel’s Study • Purebred: an organism that always produces offspring with the same form of a trait as the parent. –Example: a tall pea plant that only produces tall pea plant offspring Mendel’s Experiment • Mendel first crossed plants with opposite traits –Example: purebred tall plants with purebred short plants. • He called the parents the Pgeneration • He called the offspring the F1 generation Mendel’s Outcome • When Mendel bred a purebred tall parent with a purebred short parent, all the offspring were tall. Mendel’s Outcome Cont. • Mendel then let the F1 generation pollinate. • He discovered that the F2 generation was a mix of tall and short plants. –About 75% were tall and about 25% were short Mendel’s Results Mendel’s Conclusion • Mendel decided that there are individual factors that control the inheritance of traits and these factors exist in pairs –Female parent contributes one factor and the male parent contributes the other factor Mendel’s Conclusion • Mendel also concluded that one factor in the pair can mask, or hide, the other factor. –The tallness factor masked the shortness factor in the F1 generation. Mendel’s Conclusions today • GENES are the factors that control traits • ALLELES are the different forms of a gene –The gene that controls height has a gene for tall stems and a gene for short stems Mendel’s Conclusions today • Organisms inherit a combination of two alleles from its parents. –Either- two alleles for tall stem -two alleles for short stem -one allele for short stem and one allele for tall stem. Mendel’s Conclusions today • Individual alleles control the inheritance of traits. Some alleles are dominant, while other alleles are recessive Mendel’s Conclusions today • Dominant alleles: these traits always show up in the organism when the allele is present • Recessive alleles: these traits are masked, or covered up if a dominant allele is present. A recessive trait only shows up if the organism does NOT have the dominant allele Looking at Mendel’s Peas Again Is yellow seed controlled by a dominant or a recessive allele? What type of alleles control pinched pod shape? Understanding Mendel’s Crosses • In mendel’s first cross- he bred a purebred tall (two alleles for tall) and a purebred short (two alleles for short): as a result each offspring had one tall allele and one short allele. –Tall must be a dominant trait because it masked the short gene. Mendel’s 1st Cross •When Mendel crossed the purebred tall and the purebred short he got offspring that were all tall. •However, each offspring had one tall allele and one short allele—they were called hybrids •HYBRIDS: An organism that has two different alleles for a trait Mendel’s 2nd Cross • When Mendel crossed the hybrid plants (1 tall allele and 1 short allele): –Some plant inherited two dominant (tall) alleles: They were tall –Some plants inherited one dominant (tall) allele and one recessive (short) allele: They were tall –Some plants received two recessive (short) alleles: they were short Using Mendel’s Discoveries These rabbits have traits controlled by dominant alleles and traits controlled by recessive alleles. Black fur is dominant over the allele for white fur. • What combination of alleles must the white rabbit have? •What are the two possible allele combinations the black rabbit have? Using Symbols in Genetics • Instead of using words such as ―tall stems‖ to represent alleles, scientists use letters. • Dominant alleles are represented by a capital letter –Tall = T • Recessive alleles are represented by the lowercase version of the letter –Short= t Using Symbols in Genetics • When a plant inherits two dominant alleles for tall stems it is written TT • When a plant receives one dominant allele and one recessive allele it is written Tt • When a plant recievs two recessive alleles for short stems it is written tt End of Section Questions 1) Explain how the inheritance of traits I controlled in organisms. Use the terms genes and alleles in your explanation. 2) What is a dominant allele? What is a recessive allele? Give an example of each. End of Section Questions 3) The allele for round seeds is represented by R. Suppose that a pea plant inherited two recessive alleles for wrinkled seeds. How would you write the symbols for its alleles? 4) Can a short pea plant ever be a hybrid? Why or why not?