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Genetics and Heredity
Our Hero Gregor Mendel
Mendle’s Pea Experiment
Height-Tall vs Short Seed Shape-Round vs Wrinkled Seed Color-Yellow vs green Flower Color- Purple vs White Flower Position- Axial vs Terminal Pod shape- Inflated vs Constricted Pod Color- Green vs yellow
Anatomy of a Flower
Making A Punnett Square
GametesTT X tt
Male Female
Completed SquareTT
MaleX tt
Female
T
T
t t
Terminology
Homozygous-two of the same alleles for a given trait
Dominant
Recessive Heterozygous-each cell of an organism contains two different
alleles for a given trait
Example:
Tt X Tt
More Terminology Genotypic Ratio- the combination of alleles for a given trait (gene
combination) Phenotypic Ratio- a ratio of what the offspring look like
Test of SegregationTest cross
Rr X rr RR X rr
Mendle’s Conclusions
Principle of Dominance- one form of a hereditary trait (dominant), dominates or prevents the expression of the recessive trait.
Principle of Segregation- during gamete formation the pair of genes responsible for each trait separates so that each gamete receives only one gene for each trait.
Incomplete Dominance
Dihybrid Cross
THE PRINCIPLE OF INDEPENDENT ASSORTMENT
GENES FOR DIFFERENT TRAITS SEGREGATE INDEPENDENTLY DURING GAMETE FORMATION
Multiple Alleles-Codominance
Blood type A
Blood type B
Blood type AB
Blood type O
IAIA IA iO
IBIB IBiO
IAIB
iOiO
G e n o t y p e s
Mendel’s Work Revisited
In the early 1900’s Walter Sutton observed meiosis in grasshoppers. He concluded that chromosomes do indeed behave like Mendel had thought. It also started the idea that genes are on the chromosomes.
Thomas Hunt Morgan
His work was on fruit flies Experimented with the sex chromosomes X and Y chromosomes differ between the
sexes so they are called sex chromosomes
The other chromosomes are called autosomes
Sex DeterminationMale Female
Sex-Linked Inheritance
XRXR XrYRed Eyed Female White Eyed Male
Can We Get A White Eyed Female?XRXr XrY
Red Eyed Female White Eyed Male