11-3 Exploring Mendelian Genetics

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Think about it….

• Mendel wondered if alleles sorted independently…

• ….for example…• “…is the gene for green/yellow peas linked to

the gene for round/wrinkled peas…..• …..like….are green peas always round….or…..• …hmmmm…”

A. Independent Assortment

• 1. Mendel performed an experiment, to follow two genes going from one generation to the next, called a two-factor (dihybrid) cross.

A. Independent Assortment

• 2. First, Mendel crossed true-breeding (Homozygous) plants. Two-Factor Cross: F1

• 3. Genotypes: RRYY and rryy• Phenotypes: Round/Yellow & Wrinkled/Green.

A. Independent Assortment

• 4. All the F1 offspring had the genotype RrYy (heterozygous) and phenotype round/yellow.

A. Independent Assortment

• 5. Two-Factor Cross: F2 Mendel found that some of the offspring looked NOTHING like the parents!!

A. Independent Assortment

• 6. In conclusion ALL of a gamete’s alleles segregate independently; known as independent assortment.

A. Independent Assortment

• 7. Mendel’s results closely matched the expected ratio of 9:3:3:1.

9: Round and Yellow3: Round and Green3: Wrinkled and Yellow1: Wrinkled and Green

• In mice the ability to run normally is a dominant trait. Mice with this trait are called running mice ( R ). The recessive trait causes mice to run in circles. Mice with this trait are called waltzing mice ( r ). Hair color is also an inherited trait in mice. Black hair ( B ) is dominant over brown hair ( b ).

running mice (R), waltzing mice (r), Black hair (B), brown hair (b).

• 1. Cross a heterozygous running heterozygous black mouse with a homozygous running, homozygous black mouse.

• running mice (R), waltzing mice (r), Black hair (B), brown hair (b).

• 2. Cross a homozygous running, homozygous black mouse with a heterozygous running, brown mouse.

• running mice (R), waltzing mice (r), Black hair (B), brown hair (b).

• 3. Cross a homozygous waltzing brown mouse with a homozygous waltzing brown mouse.

• running mice (R), waltzing mice (r), Black hair (B), brown hair (b).

• 4. Cross a homozygous running, heterozygous black mouse with a homozygous waltzing brown mouse.

• running mice (R), waltzing mice (r), Black hair (B), brown hair (b).

• 5. Cross a homozygous running, brown mouse with a heterozygous running, homozygous black mouse.

• running mice (R), waltzing mice (r), Black hair (B), brown hair (b).

• 6. Cross a heterozygous running, heterozygous black mouse with a heterozygous running, heterozygous black mouse.

B. A Summary of Mendel’s Principles

• 1. Genes are passed from parents to offspring.• 2. When there are 2 alleles (form of a gene), 1

is dominant and 1 is recessive.

B. A Summary of Mendel’s Principles• 3. Most organisms have two copies of a gene,

one from each parent, that are segregated when gametes are formed (meiosis).

B. A Summary of Mendel’s Principles

• 4. Alleles segregate independently from each other (independent assortment).

How do you think this happens??

C. Beyond Dominant and Recessive Alleles

• 1. Some alleles are neither dominant or recessive, many traits are controlled by multiple genes or alleles.

C. Beyond Dominant and Recessive Alleles

• 2. Incomplete dominance occurs when one allele is not completely dominant over another. (The heterozygous phenotype is between the homozygous dominant and homozygous recessive phenotypes.)

Ex: Flower color. Red=AA, White= aa, Pink= Aa

C. Beyond Dominant and Recessive Alleles

• 3. Codominance occurs when both alleles contribute to the phenotype.

• Ex: Blood Types

C. Beyond Dominant and Recessive Alleles

• 4. Some genes have multiple alleles to create a phenotype.– Ex: Fur Color in Rabbits

C. Beyond Dominant and Recessive Alleles

• 5. Polygenic Traits are traits controlled by 2 or more genes.– Ex: Skin tone is

controlled by 4 genes.

C. Beyond Dominant and Recessive Alleles

• 6. Sex-Linked Traits express their phenotype based on the sex chromosomes.– EX: Colorblindness

Matching

• 1. Incomplete Dominance

• 2. Codominance• 3. Multiple Alleles• 4. Polygenic Traits• 5. Sex-Linked Traits

• A. Colorblindness• B. Skin Tone• C. Blood Type• D. Rabbits Fur• E. Flower color

D. Applying Mendel’s Principles

E. Genetics and the Environment