History of Genetics Mendels Work What is Genetics

History of Genetics Mendel’s Work

What is Genetics? • The science of Heredity • The way by which traits are passed from parent to offspring, or “inherited”

Who was Mendel? • Gregor Mendel was an Austrian monk who was the first to understand certain patterns of inheritance • He did so by crossing different types of pea plants in carefully planned experiments

Why pea plants? • 1. ) They have many different characteristics that have two distinct forms

Why pea plants? • 1. ) They have many different characteristics that have two distinct forms • 2. ) They are self-pollinating (can fertilize themselves) because each flower has both male and female parts

Why pea plants? • 1. ) They have many different characteristics that have two distinct forms • 2. ) They are self-pollinating (can fertilize themselves) because each flower has both male and female parts • 3. ) They are “low maintenance” plants – Easy to care for – Rapid life cycle

Mendel’s Experiment • Mendel performed crosses only looking at one trait: MONOHYBRID CROSS • Step 1: Mendel allowed plants that had each type of trait to self-pollinate for several generations (to ensure the production true-breeds). P generation • Step 2: Mendel crossed two P generation plants that had “opposite” traits. Produced F 1 generation • Step 3: Mendel allowed F 1 generation to self-pollinate. Produced F 2 generation

Mendel’s Experiment • After each pollination, Mendel recorded the number of plants that had each trait

Results to Note: • When Mendel crossed true breed purple flowers with true breed white flowers, all of the offspring in the F 1 generation had purple flowers. • After the F 1 generation was left to self-pollinate, the F 2 generation resulted in 705 purple flowered plants and 224 white flowered plants • Ratio= 705: 224 OR 3: 1 • This 3: 1 ratio was seen in all seven of the traits.

Hypotheses Based on Mendel’s Results: • 1. ) For each inherited trait, an individual has two copies of the gene – one from each parent. • 2. ) There alternative versions of genes called alleles. • 3. ) When two different alleles are present together, one of them might be completely expressed, while the other may have no effect on the physical appearance. – Expressed trait = dominant (capital letter) – Trait not expressed when dominant is present = recessive (lower case letter)

What did Mendel Think of All This? • Mendel correctly concluded that each pea has two separate “heritable factors” for each trait – one from each parent

Homozygous vs. Heterozygous • If the two alleles of a particular gene present in an individual are the same, the individual is said to be homozygous § If the alleles of a particular gene present in an individual are different, the individual is said to be heterozygous

Working with Mendel’s Rules of Genetics: • All of Mendel’s work was based upon a mathematical field that deals with how likely something is to happen, called probability • We now use devices called Punnett squares to calculate these probabilities

Working with Mendel’s Rules of Genetics: • How to set up a monohybrid Punnett square: – Draw a square and divide it into 4 squares. – Collect Parental information (Tt x tt) – Place one letter from first parent beside each row; place one letter from second parent above each column: t t – Multiply to fill each sq. T T t t t t

Working with Mendel’s Rules of Genetics: • Calculate a genotypic ratio: Genotype is genetic make-up – In this case, each offspring has a 50% chance of having the genotype Tt and a 50% chance of having the genotype tt • Calculate a phenotypic ratio: Phenotype is the physical representation of t t the gene – In this case, each offspring has T a 50% chance of being able to t roll their tongue and a 50% chance of not being able to T t t t