11-2 Probability and Punnett Squares Genetics and Probability How do geneticists use the principles...

11-2 Probability and Punnett SquaresGenetics and Probability

How do geneticists use the principles of probability?

Probability – the likelihood that a particular event will occur

The principles of probability can be used to predict the outcomes of genetic crosses.

Sexual Reproduction and GeneticsChapter 10

• Punnett Squares – a tool used to determine the combinations from a genetic cross

• Shows all possible combinations of gametes and likelihood each will occur

Punnett Squares


Setting up a Punnett Square• Draw the punnett square – size of your square depends on

how many traits you are using (Ex. 1 trait = 4 boxes, 2 traits = 16 boxes)

• Gametes produced by each parent are shown along the top and left side.

• Possible gene combinations for the offspring appear in the four boxes.


Mendel’s Experiment• Gametes from the F1

generation parents are used to get the offspring for the F2 generation.

• Mendel only looked at one trait at a time in his first experiments

• Monohybrid cross – a cross involving one trait


Probablility 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).

Mendel’s Law of Segregation

Sexual Reproduction and Genetics

Two alleles for each trait separate during meiosis. During fertilization, two alleles for that trait unite. Heterozygous organisms are called hybrids.

10.2 Mendelian Genetics

Chapter 10

Monohybrid Cross


A cross that involves hybrids for a single trait is called a monohybrid cross.


Chapter 10


Dihybrid Cross

The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.

Dihybrids are heterozygous for both traits.


Chapter 10


Law of Independent Assortment

Random distribution of alleles occurs during gamete formation

Genes on separate chromosomes sort independently during meiosis.

Each allele combination is equally likely to occur.


Chapter 10

Law of independent assortment occurs during metaphase I of meiosis.


Punnett Square—Dihybrid Cross

Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.

The resulting phenotypic ratio is 9:3:3:1.


Chapter 10

Polyploidy


Polyploidy is the occurrence of one or more extrasets of all chromosomes in an organism.

A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes.

10.3 Gene Linkage and Polyploidy

Chapter 10

11-2 Probability and Punnett Squares Genetics and Probability How do geneticists use the principles...

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