Theme 4A Flashcards
Genotype
Particular combination of alleles present in a given organism
Phenotype
Expression of a trait in an individual
What did Darwin not know about nat sel?
The mechanism of heritability (DNA)
Blending Inheritance
And why it doesn’t work
- Offspring traits are intermediate of parents
- If this was true, variation would be lost over time
- Doesn’t reflect constant presence of variation
Particulate Inheritance
Traits passed down from parents to decendants through discrete units (genes)
Gregor Mendel
- Tested blending vs partculate inheritance
- Used true-breeding peas
- Looked at 7 dif phenotypes
- Determine whether statistical patterns in the occurence of the contrasting traits persisted by means of crossing
True Breeding means same phenotype when self-crossed
3 Distinctions of Mendel’s Pea Breeding
- Used true-breeding strains
- Focused on single trait at a time
- Quantitative: Counted the progeny (aka A LOT of attempts, looking at whole tree)
Distrete Trait
Controlled by few, or often 1 gene
Dominant Vs. Recessive
- Note this isn’t always the case (mutants change things)
- Dominant allele codes for a functional protein, recessive does not
- I.e. Pea colour determined by functional enzyme that breaks down chlorophyll
Monohybrid Cross (Homozygous)
- Parental Gen (P1) cross with dif phenotype
- Filial Generation (F1) “self-fertilize” heterozygote
- F2 Gen seeds 3:1 phenotypic ratio
- Genotypic ratio of 1:2:1
Can distinguish b/w A/A plants and A/a plants genotypically, not phenotypically
Mendel’s Segregation Hypothesis
- Adults carry 2 copies of facotrs (genes) that govern inheritance of character
- If genes consist of dif alleles, 1 is dominant to the other
- Pair of alleles that control character separate as gametes (meiosis); diploid organisms get one allele from each parent
Did not explain every trait with Mendelian inheritance
Monohybrid Cross (Heterozygotes)
- Prob of a gamete inhering 1 of 2 alleles during meiosis is random
- Prob of genotype in a cross determined by the product of the probabilities of acquring each gamete from mom & dad
Product Rule
- Prob of 2 independent events occuring in succession
- Aka if prob of heads 1/2, tails 1/2, would then mean prob of 2 heads is 1/4
Sum Rule
- Prob of an outcome that can be achieved by 2 or more mutually exclusive events is the sum of their individual probs
- Prob of a heads and tails in 2 tosses, so chance of heads then tails (1/2 x 1/2 = 1/4)
or tails then heads (1/2 x 1/2 = 1/4) with total prob being 1/4 + 1/4 = 1/2
Multiplication Rule
Do 4A quiz and photo app to study, can’t rly type it
Mendel Principle of Segregation
- Each organism is diploid (2 alleles)
- Can be homozygous and heterozygous
Test Cross
- Used to determine if one is a heterozygote
- Making to individual with homozygous recessive genotype
Transmission genetics and physical basis in meiosis
Chromosomal Theory of Inheritance
- Chromosomes occur in pairs in diploid organisms
- Chromosomes of each pair separated in gametes
- Separation of each pair of chromosomes is independent of other pairs
Dominance not Universal
2 types
- Incomplete dominances: intermediate phenotype
Codominance: Both traits expressed
Incomplete Dominance
- One allele not completely dominant to other
- Heterozygote is intermediate phenotype (Red and White homozygotes, make Pink heterozygote)
- Uses superscript to label alleles (C^RC^W)
- Creates some of functional enzyme
- Makes genotypic and phenotypic ratio same
CoDominance
- Equal effects, dominant alleles fight for expression
Polyallelic/Multi-allelic/polymorphic
- Multiple forms of different alleles for the same gene
- Example - Major histocompatibility complex genes have 1000 of alleles
- Why organ transplants can fail
- Altered shape of proteins from these different alleles
Complex Traits
- Phenotypes exist on continuum, spectrum
- Polygenic - Single character controlled by multiple genes
- Genetic and environmental influences create continuous distribution
