Mendel & heredity

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• 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’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.