Introduction to Mendelian Genetics Introduction to Mendelian Genetics.
11-3 Exploring Mendelian Genetics
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Transcript of 11-3 Exploring Mendelian Genetics
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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…”
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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.
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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.
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A. Independent Assortment
• 4. All the F1 offspring had the genotype RrYy (heterozygous) and phenotype round/yellow.
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A. Independent Assortment
• 5. Two-Factor Cross: F2 Mendel found that some of the offspring looked NOTHING like the parents!!
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A. Independent Assortment
• 6. In conclusion ALL of a gamete’s alleles segregate independently; known as independent assortment.
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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
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• 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 ).
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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.
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• 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.
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• 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.
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• 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.
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• 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.
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• 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.
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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.
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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).
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B. A Summary of Mendel’s Principles
• 4. Alleles segregate independently from each other (independent assortment).
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How do you think this happens??
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C. Beyond Dominant and Recessive Alleles
• 1. Some alleles are neither dominant or recessive, many traits are controlled by multiple genes or alleles.
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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
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C. Beyond Dominant and Recessive Alleles
• 3. Codominance occurs when both alleles contribute to the phenotype.
• Ex: Blood Types
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C. Beyond Dominant and Recessive Alleles
• 4. Some genes have multiple alleles to create a phenotype.– Ex: Fur Color in Rabbits
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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.
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C. Beyond Dominant and Recessive Alleles
• 6. Sex-Linked Traits express their phenotype based on the sex chromosomes.– EX: Colorblindness
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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
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D. Applying Mendel’s Principles
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E. Genetics and the Environment