Mol Lecture #22 Flashcards
Mendelian Genetics Overview
- Thinking about the gene as a heritable unit that gives rise to some attribute. (ex. Height, eye color, etc.) (also gives rise to attributes that we cannot see)
Gregor Mendel (This flashcard isn’t terribly important)
- Mathematician, chemist, and biologist
Interested in inheritance
What did Gregor test on, and what did it reveal?
- Pea plants- pisum sativum
- Character
- Trait
Character
- specific heritable attribute (ex., flower color)
Trait
- differences in a given character (ex., white or purple)
Mendel’s single character crosses
- Usually self-fertilize or self-cross (mating ability)
→ (produce gametes and make a zygote in a single plant) - Experimentalists can control crosses and force cross-pollination to cross different plants
True-breeding strains
- Mendel’s first work uses true-breeding strains: plants that always look the same for a specific attribute (character- tall, short, purple, white)
Gregor’s Experiment setup
- Parental generation (P)
- PxP→ F1 generation→ F1 generation self-crosses→ gives rise to F2 generation
Mendel’s Results
- F1 generation showed only 1 of the parental traits for each character. (same mathematical outcome each time)
→For any character, one of the traits wins out as dominant
→ Later on, the one that didn’t win out (recessive) will show itself in very specific ways
Self-Cross
- After F1 self-crosses (heterozygous) always get, 3:1 ratio of parental traits where the 3 (of those 3:1) is showing the parental trait observed in the F1.
Mendelian Genetic Findings
1) Evidence that genes exist in pairs in individuals
- Genes are the factors or units of character, and alleles of the same genes give rise to the different traits of a given character
2) Found that traits can be dominant (won out) or recessive (did not show up)
3) Evidence that gene pairs entered gametes individually to recombine at fertilization. (when we recombine, we’re going to be able to get the recessive trait back)
Principle of segregation
- allele pairs separate or segregate during gamete formation and randomly unite at fertilization.
Homozygote
- a true breeding individual with 2 like alleles for a gene (1 gamete type for this gene)
Heterozygote
-an individual with two different alleles for a given gene (F1) (2 gamete types with respect to this gene)
Monohybrid (heterozygote for a specific gene)
- offspring of parents that are true breeding for a specific character
Phenotype
- the appearance of the individual (the physical manifestation of the attribute)
Genotype
- the alleles of a given individual that produce the phenotype.
Probability and Prediction in Mendelian Genetics
- Probability Rules→ 0-1 probability for any given thing
- Product Rule
- Sum Rule
Product Rule
- What is the probability of this AND that happening together? - multiply
Sum Rule
- What is the probability of this OR that happening? -add
Probabilities in Crosses- Punnett Square
- Invented by: Reginald Punnett
- Invented a diagrammatic way to represent crosses and determine probability.
Test Crosses (Setup & Purpose)
- For individuals showing a dominant trait for a given character, the genotype could be Pp (het) or PP (homozygous)
- In a Test Cross, we use a recessive true-breeding plant for a given character to determine the unknown genotype of the dominant trait plant.
- Mathematically determining the genotype of the parental.
