MENDEL’S EXPERIMENTS Part I: Law of Dominance Biology 12

Joke of the day:

Mendel’s experiments Studied principles of inheritance in plants Looked for general trends and created a basic set of rules about the transmission of traits Large populations, like his peas, are better to analyze statistically

Mendel studied Pea Plants. Why? The pea flower:Because…… They were easy to grow The male part of the flower (stamen) was easily removed to prevent self-pollination. Easily identifiable traits Can work with large numbers of samples

Mendel’s Peas He looked at 7 characteristics:

SO WHAT DID MENDEL FIND OUT ABOUT HIS PEA PLANTS?

Mendel’s first experiments Mendel first selected certain traits (characteristic) and bred those plants so that they would be purebred for that trait. For example, he chose plants that were tall and bred them together. He then took only the tall offspring and bred those together. He did this until only tall offspring were produced. Mendel called his purebred plants the parent generation or P generation.

Then what? For each trait, he took two plants with opposite traits and crossed them Example: purple flower plant crossed with white flower plant This is called a monohybrid cross because only one trait, flower colour, is being tested. The offspring from this cross are called the first filial generation or the F 1 generation

What did he find? Mendel found that 100% percent of the F 1 ’s had purple flowers This happened with all the traits he studied! Mendel found that one trait always appeared and the other trait vanish? The trait that appeared = dominant and he trait that disappeared = recessive

Dominant vs. recessive This is where the terms dominant and recessive came from. Example: Mendel concluded that purple flowers (PP) were dominant over white flowers (pp). Uppercase letters stand for dominant and lowercase letters for recessive Two letters are used for each trait to represent the allele from each parent Dominant (AA) Recessive (aa)

1. Law of Dominance When there are two different alleles of a gene in an individual, the allele for the dominant trait will be expressed not the recessive trait or When individuals that are pure for contrasting traits are crossed, the offspring will express only the dominant trait For example, when a purebred tall plant is crossed with a purebred short plant, all the offspring will be tall

Example: What will happen when pure yellow peas are crossed with pure green peas? Yellow is dominant and green is recessive

To do: Complete vocabulary list using pages : A. Genes B. Trait C. Genome D. Dominant E. Recessive F. Allele G. Genotype H. Phenotype I. Homozygous J. Heterozygous K. Monohybrid cross L. Punnett square Watch first 3 sections of “Greatest discoveries in Genetics” video