# Mendelian Genetics The principles of probability can be used to predict the outcome of genetic crosses Probability - The likelihood that a particular event.

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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%.

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

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?

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

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

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

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.

Mendel’s Genetic Crosses
P generation F1 generation F2 generation

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

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.

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

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)

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!

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

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

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

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

Two Factor Cross Results

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

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

Mendel’s Actual Results

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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