Mendel & heredity

Heredity- transmission of traits from parent to offspring. Genetics- the study of heredity

Gregor Mendel The “father” of genetics Austrian monk Studied the garden pea to develop a set of rules to predict the patterns of heredity.

Mendel used the garden pea because: It grows quickly Has many varieties Able to self-pollinate or true breed

Mendel’s experiments 1. produced a true-breeding P generation (parent) 2. produced the next generation, F1 (filial) generation, by cross pollinating plants. 3. produced 3rd generation, F2 (filial) generation by self- pollination See picture

Mendel thought that certain “factors” were passing on traits. Mendel’s Theories Mendel thought that certain “factors” were passing on traits. We now know the factors are genes.

An organism has 2 genes for each trait. One gene came from the female gamete and one from the male gamete.

Meiosis

Simple patterns of Heredity aka principle of dominance Dominant gene- the gene that can cover up a recessive gene Recessive gene- the gene that can be covered up.

If you have one dominant gene and one recessive gene you will have the dominant trait. If you have two dominant genes you will have the dominant trait. If you have two recessive genes you will have the recessive trait.

Examples in peas Cross Result Tall X short Tall Green pea X Yellow pea Yellow pea Smooth pea X wrinkled pea Smooth pea

Use Upper case letter for dominant gene ex- T is for tall pea plant Use lower case letter for recessive gene ex- t is for short pea plant

Homozygous- if both genes for the trait are the same ex-TT Heterozygous- if the genes for the trait are different ex- Tt Allele- one of the copies of a gene ex- T Phenotype- the visible trait of the organism. Ex- Tall Genotype- the combination of genes for a trait. Ex- TT, Tt, or tt

Mendel’s Laws 1. The Law of Segregation: Two alleles for a trait separate during the formation of gametes.

2. The Law of Independent Assortment: alleles for different traits separate independently of one another during formation of gametes if they are on different chromosomes. ex- the gene for eye color separates independently of the gene for hair color.

In humans, 6 fingers on one hand is dominant and 5 fingers is recessive. 1. What is the genotype of an individual that is homozygous dominant? 2. What is the phenotype of an individual that is homozygous dominant? 3. What is the genotype of an individual that is heterozygous? 4. What is the phenotype of an individual that is heterozygous? 5. What is the genotype of an individual with 5 fingers?

Complex Patterns of Inheritance 1. Incomplete dominance- a heterozygous individual show a trait that is a blend of the 2 genes. Ex- snapdragons- if flower has a dominant red allele and a recessive white allele the flower is pink.

2. Codominance- 2 different dominant alleles can be expressed at the same time in heterozygous individuals. Ex- Roan color in horses. Both red and white hair color genes are dominant. The horse has red hairs and white hairs.

3. Multiple alleles- some traits have more than 2 alleles that determine it. Ex- 3 alleles determine blood type A, B, and O

Polygenic Inheritance More than one gene effects the trait. Ex- height, weight, skin color Only about 600 traits in humans are determined only from one gene.