Genetics

• Heredity- passing of traits from parent to offspring

• Traits- hair color, eye color, height, etc. (are like your parents)

• -characteristics that are inherited• Genetics- the study of heredity

Gregor Mendel

• Gregor Mendel- Austrian Monk (mid 1800’s) is considered the “Father of Genetics”

• -studied pea plants (Pisum sativum) to explain heredity

Why study pea plants?

• 1. Pea plants have easy traits to identify (32 varieties of traits, he chose 7 to study)• ex. Flower color, seed color, seed shape• 2. Pea plants are small, easy to grow, and produce

large number of offspring • -allowed Mendel to have something to count (used

ratios)

• Mendel’s pea plant traits he studied

Why Study Pea Plants

• 3. Pea plants have the ability to self-pollinate (both male and female parts on same flower) or cross-pollinate

Self-Pollination

• Involves having the pollen (male sperm) be directly deposited on the female section of the flower

Cross- Pollination

• Requires the removal of the malestamen (makes pollen) on 1st flower and transferring thepollen from a different flower to the first one

Mendel’s Pea Plant Experiments

• -he studied 3 generations of pea plants (parents, kids, grandkids)

• 1. Parents had to be true breeding (pure plants) in which the same trait is expressed in all offspring when pea plant is self-pollinated

• -called the parental generation (P1)

Mendel’s Pea Plant Experiments

• 2. Mendel cross-pollinated 2 varieties (1 true breeding tall and 1 true breeding short plant) from the P1 generation• 3. This produced the F1 (“filial” or kids) generation *It was amazing to Mendel that all of the kids

were tall and none of them were short!-it appeared as if the short parent had never existed!

Mendel’s Pea Plant Experiments

• 4. He then allowed the F1 generation to self- pollinate which produced the F2 (grandkids) generation *He noticed that some of the grandkids were tall and others were short (he counted them and

found that there was a 3:1 ratio of tall to short plants in the F2 generation)

*The short trait reappeared as if from nowhere!

Results of Mendel’s cross of true breeding short with a true breeding tall pea plant

Mendel saw the same results in different traits

Mendel’s pea experiments

Mendel’s Theory of Heredity

• 1. Parents pass on units of information to offspring . He called “traits”= genes.

• -don’t pass trait directly because only the unit is passed

• 2. 1 unit from mother + 1 unit from father• (gene in egg) (gene in sperm)

2 units for each trait

Alleles on homologous chromosomes

• *These alternative forms of a gene that code for a trait are called alleles. There are 2 alleles for each trait; 1 allele for a trait is from mom and 1 allele is from dad.

Homozygous vs. Heterozygous

• Homozygous- if the 2 alleles for a trait are the same

• TT (homozygous dominate)• tt (homozygous recessive)• Heterozygous- if the 2 alleles for a trait are

different• -Tt

Genotype

• Genotype- the allele combination an organism has for a trait

• -ex. TT is the genotype (genetic formula) of a tall plant that has 2 alleles for tallness

Phenotype

• Phenotype- “physical appearance” of an organism or the way it looks and behaves

• -determined by the genotype • -the phenotype of a tall plant is tall whether it

is TT or Tt and the phenotype of a short plant is short only if it is tt.

• 3. The presence of an allele does not guarantee it will be expressed.

• -Only the dominant allele is expressed in heterozygous individuals and the recessive allele is not expressed

• Ex. a Tt individual will appear tall

Law of Segregation

• Alleles are passed from one generation to the next by the Law of Segregation which says that the 2 alleles (genes) for each trait must separate when gametes are formed.

Law of Segregation and Meiosis

Law of Segregation

• Also, the Law of Independent Assortment is followed which says the pairs of alleles for different traits separate independently of one another during gamete formation.

• In other words the inheritance of one trait has no influence on the inheritance of another trait.

Law of independent assortment