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Mendelian Genetics The principles of probability can be used to predict the outcome of genetic crosses Probability - The likelihood that a particular event will occur is called probability. When a baby is born, the probability that it is a girl is 1:2 or 50%.

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**Probability and Genetics**

Probability and Product Rule: How do you calculate the probability of more than one event occurring? Product Rule = Multiply the probability of each independent event together

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**Probability and Genetics**

Example: What is the chance that a couple (both heterozygous for tongue rolling) will produce a baby girl who can roll her tongue?

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**Probability and Genetics**

Begin by determining the probability of each event happening independently: What is the probability of producing a baby girl? ____________ 50% or 1/2

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**Probability and Genetics**

What is the chance that a couple (both heterozygous for tongue rolling) will produce a child who can roll its tongue? Set up a Punnett Square! ________________ R r 75% or 3/4 R r RR Rr Rr rr

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**Probability and Genetics**

The original question: What is the chance that a couple (both heterozygous for tongue rolling) will produce a baby girl who can roll her tongue? ________________ What is the chance that this couple will produce a baby girl who cannot roll her tongue? ________________ ½ x ¾ = 3/8 ½ x ¼ = 1/8

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Gregor Mendel Mendel began his genetic research by crossing true-breeding pea plants, the P(arent) generation. The result of this cross is the F1 generation, which are hybrids. He next crossed the F1 generation to produce the F2 generation.

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**Mendel’s Genetic Crosses**

P generation F1 generation F2 generation

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**Mendel’s Research on 1 Trait**

What is the phenotype ratio of F2 generation? What is the genotype ratio of F2 generation? 3 violet flowers:1 white flower 1 BB: 2Bb: 1bb

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**Mendel’s Law of Segregation**

Mendel recognized that each pea plant had two alleles for a trait. He hypothesized that one allele came from each of the two parent plants. Mendel’s law of segregation states: Allele pairs separate during gamete (sex cell) formation, and randomly unite at fertilization.

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**Half the number of chromosomes as the parent cell**

Production of Gametes Half the number of chromosomes as the parent cell

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The Two-Factor Cross Mendel next tested whether the segregation of alleles for one trait (example seed shape: round or wrinkled) affects the segregation of a second trait (example seed color: yellow or green)

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The Two-Factor Cross One plant was true breeding for both yellow AND round seeds = P generation This plant’s genotype was YYRR The only alleles that could be produced by this plant were… Pass out whiteboards!

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The Two-Factor Cross The second plant was true breeding for both wrinkled AND green seeds = P generation This plant’s genotype was yyrr The only alleles that could be produced by this plant were… yr

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**The Two Factor Cross The only possible result of this cross is …**

YR YR RrYy = F1 generation What is the phenotype of the offspring? Round and yellow seeds. YyRr YyRr yr YyRr YyRr

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The Two-Factor Cross Mendel next crossed the offspring of the F1 generation. He crossed YyRr with YyRr. Each plant is called a dihybrid. Which alleles are created from YyRr? Work this out on your whiteboard! YR yR Yr yr

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**The Two Factor Cross YR yR Yr yr YR yR Yr yr r yr**

Draw a 16 box Punnett Square to show the cross between YyRr and YyRr Begin by showing the possible alleles. Then fill in the boxes! YR yR Yr yr r yr

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**Two Factor Cross Results**

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The Two Factor Cross What is the phenotype ratio for a two factor cross between dihybrids? Write on whiteboard! ___________dominant for both traits – yellow and round seeds ___________dominant for one trait and recessive for the second – yellow and wrinkled seeds 9 3

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The Two Factor Cross 3 ___________recessive for one trait and dominant for the second – green and round ___________recessive for both traits – green and wrinkled 1 Phenotype ratio – 9:3:3:1

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**Mendel’s Actual Results**

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**Mendel’s 4th Conclusion**

Principle of Independent Assortment - genes for different traits can segregate INDEPENDENTLY during the formation of gametes. For example: A person can have blonde hair and blue eyes or brown hair and blue eyes. Hair color and eye color are inherited independently of each other.

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Chapter 11: Introduction to Genetics

Chapter 11: Introduction to Genetics

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