Section 12.2Applying Mendel’s Principles

Standard

• LS3.3 Through pedigree analysis, identify patterns of trait inheritance to predict family member genotypes. Use mathematical thinking to predict the likelihood of various types of trait transmission.

I Can…

• LS 3.3 I can determine the probability of a particular trait in offspring based on the genotype of the parents.

Key Questions

1. How can we use probability to predict traits?

2. How do alleles segregate when more than one gene is involved?

3. What did Mendel contribute to our understanding of genetics?

Vocabulary

• Probability

• Homozygous

• Heterozygous

• Phenotype

• Genotype

• Punnett square

• Independent assortment

Probability and Heredity

• Probability- the likelihood that a particular event will occur

• Flipping a coin once. Probability of landing on heads?• ½

• Flipping a coin three times. Probability of landing on heads every time?• (½)(½)(½) = 1/8

• The way alleles segregate during gamete formation is random, like a coin flip.

Punnett Square-Fill in the boxes for

the possible offspring

G

g

G

g

Probabilities Predict Averages

• If you flip a coin twice, you are likely to get one heads and one tails.

• However, you could also get two heads or two tails.

• To get the expected 50:50 ratio, you might have to flip the coin many times.

• The same is true of genetics.

• Statistically, the larger the # of offspring, the closer the results will be to the predicted values.

Homozygous vs. Heterozygous

• Homozygous- organisms that have two identical alleles for a particular gene• GG = homozygous dominant

• gg = homozygous recessive

• Heterozygous- organisms that have two different alleles for the same gene • Gg

Genotype vs. Phenotype

• Genotype- genetic makeup

• Phenotype- physical trait

• Simple dominance example• GG and Gg genotypes = green phenotype

• gg genotype = yellow phenotype

Using Punnett Squares

• Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses.

One-Factor Cross = Monohybrid Cross

Monohybrid Cross

• What is the genotypic ratio?• GG : Gg : gg

• What is the phenotypic ratio? • dom : rec

G

g

G

g

Independent Assortment

• The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

• Independent assortment helps account for the many genetic variations observed in organisms—even when they have the same parents.

• Mendel determined this by doing a two-factor cross.

Two-Factor Cross = Dihybrid Cross

• Genes for seed shape and genes for seed color do not influence each other’s inheritance

• 9:3:3:1 phenotypic ratio

• 9- yellow and round

• 3- green and round

• 3- yellow and wrinkled

• 1- green and wrinkled

A Summary of Mendel’s Principles

• Mendel’s principles of heredity, observed through patterns of inheritance, form the basis of heredity.

• They do not apply only to plants.

• In the early 1900s, Thomas Hunt Morgan studied genetics through the use of the common fruit fly, Drosophila melanogaster.

A Summary of Mendel’s Principles

1. Inheritance is determined by units called genes, which are passed from parents to offspring.

2. When two or more forms (alleles) of a gene for a single trait exist, some alleles may be dominant and others ma be recessive.

3. In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These genes segregate from each other when gametes are formed.

4. Alleles for different genes usually segregate independently from each other.

Section 12.2 Exit Ticket

1. What is the difference between a genotype and phenotype?

2. How can a Punnett square be used to mathematically predict the genotypes of the offspring of two parents?

3. How does the principle of independent assortment help explain Mendel’s results?

The End ☺