BIO152H5 Lecture 4: BIO152 intro to genetics

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11 Oct 2015
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BIO152: Lecture 6—Introduction to Genetics
Questions Mendel was trying to answer?
- H1: blending inheritance
- H2: inheritance of acquired characteristics
character: heritable feature that varies among individuals
trait: a variant for a character
gene: hereditary determinant for a trait
allele: different version of a gene (alternate forms of a gene, ex. 1 from 1 parent and 1 from 2nd
parent)
genotype: the alleles found in an individual (always reflects the phenotype)
phenotype: physical appearance that expresses the genotype
homozygous: an organism with a pair of identical alleles for a character
heterozygous: an organism with 2 different alleles for a character
To make cross pollination controlled Mendel took off the male parts of the flower and added
pollen from a different flower. This allowed him to have full control over which flowers
pollenate etc.
Mendel’s Experiments
true-breeding: individuals that produce offspring like themselves over many generations of
self- pollination
hybridization: created by mating two true- breeding varieties
P – parental generation (true-breeding parents)
F1 – first generation
F2 – second generation
Discovered dominant recessive relationship from F2 generation.
What Mendel Observed
• For all seven pairs of contrasting traits:
1. The F1 generation showed only one of the two parental traits
• dominant trait (trait expressed)
• recessive trait (not expressed)
• In genetics, the terms dominant and recessive identify only which phenotype is observed in
individuals carrying two different genetic traits
2. The F2 generation showed an ~ 3:1 ratio of the dominant:recessive parental traits
Explaining the 3:1 ratio of phenotypes in the F2 generation
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