Mendel and the Gene Idea

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Slide 38

Fig. 14-8b

RESULTS

Phenotypic ratio approximately 9:3:3:1

315

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32

Slide 39

Using a dihybrid cross, Mendel developed the law of independent assortment

The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation

Strictly speaking, this law applies only to genes on different, nonhomologous chromosomes

Genes located near each other on the same chromosome tend to be inherited together

Slide 40

Concept 14.2: The laws of probability govern Mendelian inheritance

Mendel’s laws of segregation and independent assortment reflect the rules of probability

When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss

In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles

Slide 41

The Multiplication and Addition Rules Applied to Monohybrid Crosses

The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities

Probability in an F1 monohybrid cross can be determined using the multiplication rule

Segregation in a heterozygous plant is like flipping a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive allele

Slide 42

Fig. 14-9

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Segregation of

alleles into eggs

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Segregation of

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Slide 43

The rule of addition states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities

The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous

Slide 44

Solving Complex Genetics Problems with the Rules of Probability

We can apply the multiplication and addition rules to predict the outcome of crosses involving multiple characters

A dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously