Mendel’s Work

The Science of Heredity

Genetics- science involving the study of heredity; how traits are passed from one generation to the next

Gregor Mendel (1822-1884)Father of Genetics

Claim to Fame• Experimented with pea plants (34 varieties)• Crossed plants with various traits tall, short, blossom color, pod color, pea

color, pod texture.• Discovered that the parent plants produced offspring with particular characteristics

Mendel’s Experiments• Offspring were able to produce

“recessive” traits that existed in one of the parents that were

not expressed visibly in the offspring themselves but were expressed in the next generation• E.G.: Tall plants (from tall x short parents) were able to produce short offspring

Results:• Dominant trait always appeared

(no mixing/blending of traits)

• Recessive trait sometimes appeared in the next generation

Traits• Dominant Allele = trait that is expressed

when 2 different genes for a trait are present– represented with capital letters Y, T

• Recessive Allele = trait which is not expressed when a dominant gene for a trait is present– represented with lower case letters y, t

• P Generation = beginning Parental Generation

• F1 Generation = First Filial Generation• F2 Generation = Second Filial Generation

Purebred = organism with genes for a particular trait that are alike YY, yy, BB, bbHybrid = organism with genes for a particular trait that are different Yy, Bb

Punnett Squares• Developed by English geneticist Reginald C. Punnett•What is a Punnett Square?–Chart that shows possible gene combinations in a cross between 2 organisms

Let’s try it!!!

Phenotype and Genotype• Phenotype = physical

appearance of an organism• Genotype = its actual genetic makeup (represented with capital and/or lower case letters)

BB & Bb are alike phenotypically (both are black) but different genotypically (genetically)

•Homozygous- when 2 genes for a particular trait are the same (TT or tt)•Heterozygous- having 2 different forms of a gene for a particular trait (Tt)

Incomplete DominanceSome genes are neither dominant nor recessive, traits appear to be blended together

Examples: 4 o’clock flower, palomino (horse)

Cross between chestnut brown & a white horse = Palomino