genetics punnett squares and mendel. copyright pearson prentice hall genes and dominance mendel’s...
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GeneticsPunnett Squares and Mendel
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Genes and DominanceMendel’s F1 Crosses on Pea Plants
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Genes and DominanceMendel’s Seven F1 Crosses on Pea PlantsMendel’s F1 Crosses on Pea Plants
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Genes and Dominance
What is the principle of dominance?
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Genes and Dominance
The principle of dominance states that some alleles are dominant and others are recessive.
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Mendel's F2 Generation
P GenerationF1 Generation
Tall Tall Tall Tall Tall TallShort Short
F2 Generation
Segregation
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Segregation
The reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or segregated, from the allele for tallness.
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Segregation Alleles separate during gamete formation.
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Punnett Squares
How do geneticists use Punnett squares?
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A capital letter represents the dominant allele for tall.
A lowercase letter represents the recessive allele for short.
In this example,
T = tall
t = short
Punnett Squares
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Punnett Squares
Possible gene combinations for the F2 offspring appear in the four boxes.
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Punnett Squares
Organisms that have two identical alleles for a particular trait are said to be homozygous.
Organisms that have two different alleles for the same trait are heterozygous.
Homozygous organisms are true-breeding for a particular trait.
Heterozygous organisms are hybrid for a particular trait.
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Punnett Squares
All of the tall plants have the same phenotype, or physical characteristics. (What it LOOKS like)
The tall plants do not have the same genotype, or genetic makeup.(The alleles that make up the characteristics)
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Punnett Squares
The plants have different genotypes (TT and Tt), but they have the same phenotype (tall).
TTHomozygous
TtHeterozygous
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Probability and
Segregation
Probability and Segregation
One fourth (1/4) of the F2 plants have two alleles for tallness (TT).
2/4 or 1/2 have one allele for tall (T), and one for short (t).
One fourth (1/4) of the F2 have two alleles for short (tt).