Intro to Mendelian Genetics

Gregor Mendel Austrian monk and gardener Significant work done in 1850’s Father of genetics (study of heredity) Heredity = passing on of traits from parent to offspring Traits = characteristics that are inherited (ex. eye color)

Mendel’s First Experiment P (Parent) Generation X Purebred tall (≥ 6 ft.)Purebred short (≤ 2 ft.) ↓ Cross - pollinate

Mendel’s First Experiment F 1 (filial) Generation all tall ↓ Self - pollinate

Mendel’s First Experiment F 2 Generation ¾ tall¼ short

Mendel’s life… Mendel tried out different pea plant traits…

Mendel’s life… Thousands of times…

Mendel’s life… And got the same results! – In F 1 generation, one trait remained and the other disappeared. – In F 2 generation, the ratio of plants was ¾ to ¼

What Mendel knew… (1800s) Each parent contributes to the traits of a plant/child. Something is passed on from parent to child to contribute to the traits. Some traits were disappearing, then returning in future generations.

What Mendel didn’t know… Chromosomes were being inherited from parents. (1930s) DNA specifically is the molecule being that gives us our traits. (1920s – 1950s) What DNA is made of. (1953)

Mendel’s Rules and Laws After 1000s of experiments, Mendel came up with some “rules of heredity”: 1.Rule of Unit Factors EACH ORGANISM HAS 2 COPIES OF A GENE THAT CONTROLS EACH TRAIT; ONE COPY CAME FROM THE MALE PARENT AND ONE COPY CAME FROM THE FEMALE PARENT

each chromosome has genes (a gene is a segment of DNA that controls a trait – ex. height) there can be different forms (versions) of the same gene; these different forms are called alleles – ex. for the height gene, the alleles are tall and short the offspring get 2 copies of the gene and can inherit any combination of two alleles from the parents: Allele from your mom…Allele from your dad… tall short tall

Mendel’s Rules and Laws 2.Rule of Dominance ALLELES CAN BE DOMINANT OR RECESSIVE; THE DOMINANT ALLELE, IF PRESENT, COMPLETELY MASKS THE RECESSIVE ALLELE Dominant allele - remained in the F1 generation (ex. tall) Recessive allele - disappeared in F1 (ex. short) So we say that tall is dominant to short

When writing alleles, follow these rules: – Use the same letter for different forms of the same gene. – Use uppercase letter for dominant allele. – Use lowercase letter for recessive allele. – Always write dominant allele first. Example: height_______ = tall _______ = short A plant can be: TT __________ Tt__________ tt__________ T t tall short

Important Vocab PHENOTYPE = written description of appearance or behavior Examples: tall and short BUT, two organisms can look the same but have different gene (or allele) combinations: GENOTYPE = 2 – letter gene combination Examples: TT, Tt, tt

There are 3 different types of genotypes: ____________________________________(TT) ____________________________________(tt) ____________________________________ (Tt) Homo- means _______________________ Hetero- means _______________________ FYI:homozygous is the same as PUREBRED heterozygous is the same as HYBRID Homozygous dominant Homozygous recessive Heterozygous same different

DescriptionGenotype or Phenotype? Homozygous or Heterozygous? Red hair GG mm White eyes Short toe Dd JUST A LITTLE PRACTICE phenotype genotype N/A Homozygous (dominant) Homozygous (recessive) Heterozygous

Mendel’s Rules and Laws 3.Law of Segregation THE TWO ALLELES THAT CONTROL EACH TRAIL WILL SEPARATE DURING GAMETE FORMATION

Explains how two tall plants can give offspring that are ¾ tall and ¼ short! PLANT 1PLANT 2 Tt XTt Plant 1’s gametes:Plant 2’s gametes: All possible gamete combinations result in the following offspring:____________________ and ____________ T T t t TT, Tt, and Tt (3/4 tall)tt (1/4 short)

An easier way to determine offspring… Reginald Punnett (early 1900s) Discovered short-hand way to solve genetics problems Works based on Mendel’s law of segregation

AND NOW WE… PRACTICE, PRACTICE, PRACTICE!