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Gregor Mendel
• Father of modern genetics
• Researched with pea plants
• Developed ideas of dominance and trait segregation
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL•Seed color - green or YELLOW
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL•Seed color - green or YELLOW•Seed shape - wrinkled or ROUND
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL•Seed color - green or YELLOW•Seed shape - wrinkled or ROUND•Seed coat color - white or GRAY
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL•Seed color - green or YELLOW•Seed shape - wrinkled or ROUND•Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL•Seed color - green or YELLOW•Seed shape - wrinkled or ROUND•Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH•Pod color - yellow or GREEN
Mendelian GeneticsMendel studied a number of characteristics in pea plants including:
•Height - short or TALL•Seed color - green or YELLOW•Seed shape - wrinkled or ROUND•Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH•Pod color - yellow or GREEN•Flower position - terminal or AXIAL
Mendelian GeneticsWe will work the following three:
•Height - short or TALL•Seed color - green or YELLOW•Seed shape - wrinkled or ROUND•Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH•Pod color - yellow or GREEN•Flower position - terminal or AXIAL
Predicting Inheritance
To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes.
UPPERCASE letters are used to represent dominant genes.
lowercase letters are used to represent recessive genes.
Predicting Inheritance
For example:T = represents the gene for TALL in pea plantst = represents the gene for short in pea plants
So:TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant.
Remember there are two genes for every trait!
Predicting Inheritance
For example:T = represents the gene for TALL in pea plantst = represents the gene for short in pea plants
So:TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant.
Remember there are two genes for every trait!
Mendels’ Principle of Dominance
Some genes (alleles) are dominant and others are recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene.
Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a short plant (tt).Each plant will give only one of its’ two genes to the offspring or F1 generation.
TT x tt
T T t t
Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a short plant (tt).Each plant will give only one of its’ two genes to the offspring or F1 generation.
TT x tt
T T t t
Mendels’ “Law” of Segregation
Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait.
Punnett Squares
Tt Tt
Tt Tt
The genes from one parent go here.
The genes from the other parent go here.
Interpreting the ResultsThe genotype for all the offspring is Tt.The genotype ratio is:
Tt - 4/4
The phenotype for all the offspring is tall.The phenotype ratio is:
tall - 4/4
Punnett Squares
T t
T TT Tt
t Tt tt
Next, give the genotype and phenotype ratios of the offspring (F2 generation).
Punnett Squares
T t
T TT Tt
t Tt tt
Genotype ratio: TT - 1, Tt - 2, tt - 1
Phenotype ratio: Tall - 3
Punnett Squares
T t
T TT Tt
t Tt tt
Genotype ratio: TT - 1, Tt - 2, tt - 1
Phenotype ratio: Tall - 3, short - 1
Punnett Squares
T t
T TT Tt
t Tt tt
This is a monohybrid cross. We worked with only one trait. The height of the plant.
Punnett Squares
T t
T TT Tt
t Tt tt
This is a monohybrid cross. We worked with only one trait. The height of the plant.
Tomorrow we will work with a dihybrid cross, using the height of the plant and either seed color or seed shape.
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