Mendel’s Laws of Heredity-Why we look the way we look... EQ: What is the significance of Mendel’s experiments to the study of genetics?

What is heredity? The passing on of characteristics (traits) from parents to offspring Genetics is the study of biological inheritance and variation in organisms.

Mendel used peas...

Mendel’s Pea Plants They reproduce sexually through self-pollination Have both sex organs with two distinct, male and female, sex cells called gametes Fertilization = sperm + egg

Mendel crossed them Cross - combining gametes from parents with different traits Line of plants (offspring) became purebred, genetically uniform

Genes and Alleles Genes - located on chromosomes, they control how an organism develops and looks Each organism has two alleles for each trait Alleles - different forms of the same gene

What Did Mendel Find? He discovered three laws and rules that explain factors affecting heredity.

1. Rule of Dominance The trait that is observed in the offspring is the dominant trait expressed no matter what when present*** The trait that disappears in the offspring is the recessive trait only expressed when two copies of the allele are present**

Rule of Dominance

2. Law of Segregation Organisms inherit two copies of each gene, one from each parent. The two alleles for a trait must separate when gametes are formed during Meiosis A parent randomly passes only one allele for each trait to each offspring **

3. Law of Independent Assortment The genes for different traits are inherited independently of each other.

Phenotype & Genotype Phenotype - the way an organism looks red hair or brown hair Genotype - the gene combination of an organism AA or Aa or aa

Heterozygous & Homozygous Heterozygous - if the two alleles for a trait are different (Aa) (one dominant & one recessive ) Homozygous - if the two alleles for a trait are the same (AA or aa) (both dominant Or both recessive)