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Punnett squares illustrate genetic crosses.

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Presentation on theme: "Punnett squares illustrate genetic crosses."— Presentation transcript:

1 KEY CONCEPT The inheritance of traits follows the rules of probability.

2 Punnett squares illustrate genetic crosses.
The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. The axes represent the possible gametes of each parent. The grid boxes show the possible genotypes of the offspring. The Punnett square yields the ratio of possible genotypes and phenotypes.

3 A monohybrid cross involves one trait.
Monohybrid crosses examine the inheritance of only one specific trait. -genotypic ratio is 4 Ff -Phenotypic ratio is 4 purple

4 Ratios: -Genotypic: 1:2:1 -Phenotypic: 3:1

5 A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype. Genotypic Ratio is 2Ff:2ff = 2:2 = 1:1 -Phenotypic Ratio is 2 purple:2 white = 2:2 = 1:1

6 A dihybrid cross involves two traits.
Ratio: Mendel’s crossed heterozygous plants with 2 traits Always yielded a 9:3:3:1 phenotypic ratio. The law of independent assortment states that allele pairs separate independently of each other during meiosis.

7 Heredity patterns can be calculated with probability.
Probability is the likelihood that something will happen. Probability applies to random events such as meiosis and fertilization.

8 3:1 ratio if you look at one trait at a time (3 are one type:1 is another)
3 dominant:1 recessive 3 tall plants:1 short plant 9:3:3:1 ratio if you look at two heterozygous plants at a time 9 both dominant: 3 dominant, recessive: 3 recessive, dominant: 1 both recessive


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