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 (32 varieties of traits, he chose 7 to study) study)  ex. Flower color, seed color, seed shape 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 male stamen (makes pollen) on 1 st flower and transferring the pollen 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 true breeding tall and 1 true breeding short plant) from the P1 generation short plant) from the P1 generation  3. This produced the F1 (“filial” or zygote/kid possibilities) generation zygote/kid possibilities) 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! never existed!

Mendel’s Pea Plant Experiments  4. He then allowed the F1 generation to self- pollinate which produced the F2 (grandkids) pollinate which produced the F2 (grandkids) generation generation *He noticed that some of the grandkids were *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) 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 *The short trait reappeared as if from nowhere! 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 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.

Karyotype- Autosomal (#1-22) vs. Sex-linked traits (#23)

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