Gregor Mendel: The Father of Genetics

Mendel’s Studies Austrian Monk 1800’s Studied inheritance Used pea plants Mendel Clip

Mendel’s Work Dominant Trait – the observed trait that covers another trait (written as an upper case letter). Recessive Trait – trait that can be covered by a dominant trait (written as a lower case letter). Tall is dominant in pea plants, so the gene for tallness is represented by an upper case “T” and shortness is represented by a lower-case “t”.

Alleles Allele - Alternative forms of a gene for each variation of a trait (like T or t for tallness in pea plants). During sexual reproduction, parents pass on one allele for each trait to their offspring.

Phenotype & Genotype Phenotype Genotype The way an organism looks and behaves Ex. Tall, yellow, blond, blue eyes Genotype The gene combination an organism contains Ex. TT or Tt for tall Homozygous – two alleles are the same, TT Heterozygous – two alleles are different, Tt

Mendel’s Experiment Mendel crossed tall pea plants with short plants. He expected the offspring to be either a height somewhere between the heights of the parent plants or to get some tall offspring and some short offspring. He was surprised that all of the offspring were tall! What happened to the short trait?

Mendel’s experiment Mendel then crossed two of the offspring to see what their offspring would look like. He was surprised to see the short trait resurfaced! 1 out of every four plants was short. So, he inferred that the short trait was somehow “masked” by the tall trait in the first generation.

Punnett Squares Punnett Squares are used to predict the genotypes and phenotypes of the offspring when the genotypes of the parents is known. http://www.youtube.com/watch?v=d4izVAkhMPQ

Let’s Draw What Mendel Did! Mendel’s original parent plants (this is called the P1 generation) were each homozygous tall and homozygous short. Let’s draw a Punnett Square to illustrate this cross and the offspring that would result.

Let’s Draw What Mendel Did! Mendel’s original parent plants (this is called the P1 generation) were each homozygous tall and homozygous short. T t T TT Tt t Tt tt

Mendel’s Experiment Next, let’s draw another Punnett Square to illustrate the cross between these offspring and the possible genotypes of their offspring. This is exactly what Mendel saw.

Mendel’s Experiment Tt crossed TT Tt crossed Tt Tt crossed tt