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Explore links between DNA, chromosomes, and trait inheritance. Topics include exceptions to Mendel's rules, incomplete dominance, codominance, multiple alleles, and polygenic traits. Discover the ABO blood system, polygenic inheritance, and environmental influences on genotype-phenotype relationships.
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Unit 3 – Genetics • Today’s agenda: • Test corrections • Mini-lecture • Practice I can explain the relationships between DNA and chromosomes and explain how traits are passed from parents to offspring
Exceptions to Mendel rules Incomplete dominance Codominance Multiple alleles
Incomplete Dominance Incomplete Dominance- Situation in which one allele is not completely dominant over another. Incomplete dominance will result in a combined/intermediate phenotype
Incomplete dominance - Example • Example – Red and white flowers are crossed and pink flowers are produced.
Codominance Situation in which both alleles of a gene contribute to the phenotype of the organism BB- Black Mixture WW- white
Codominance - Example Example – A solid white cow is crossed with a solid brown cow and the resulting offspring are spotted brown and white (called roan). +
Codominance CC- coat RR- shirt CR- coat & shirt (both!)
Incomplete dominance vs codominance https://www.youtube.com/watch?v=VG0Ktdpj7Rg
Multiple Alleles and polygenic traits https://www.youtube.com/watch?v=9O5JQqlngFY Watch the video clip and write down three things you learned from it
Blood type https://www.youtube.com/watch?v=9O5JQqlngFY Why are people with type O considered universal donors?
Multiple Alleles and polygenic traits How many genotypes? How many phenotype? Situation in which there are three or more alleles of the same gene. https://www.youtube.com/watch?v=9O5JQqlngFY
The ABO blood system Note: • Blood types A and B have two possible genotypes – homozygous and heterozygous • Blood types AB and O only have one genotype each.
Punnet Square for blood type Three alleles exist (IA, IB, and i), which results in four different possible blood types
Multiple alleles Eye color, hair color, and skin color are polygenic traits. Polygenic traits result from many genes.
Gametes ABC ABc AbC Abc aBC aBc abC abc ABC AABBCC AABBCc AABbCc AaBBCC ABc AbC Abc AAbbcc aBC aaBBCc aBc abC abc aaBbcc Polygenic Inheritance of Skin Color The table shows typical ranges of skin color combinations.
Multiple Alleles • There Are Always Multiple Alleles! • Genetic inheritance is often presented with straightforward examples involving only two alleles with clear-cut dominance. This makes inheritance patterns easy to see. • BUT very few traits actually only have two alleles with clear-cut dominance. As we learn more about genetics, we have found that there are often hundreds of alleles for any particular gene.
The Power of Environmental factors Genotype Phenotype (Genetic Variant) (Organismal Trait) Environmental Influences
Identical Twin Studies Identical twins who are raised apart can have differences that last a lifetime.
Check for understanding Unlike the traits studied by Mendel, most traits are produced by genes with • sex linkage • only one allele • dominance and recessiveness • multiple alleles
Check for understanding A plant that is homozygous for red flowers is crossed with a plant that is homozygous for white flowers. In the case of incomplete dominance, the flowers of the offspring will be • red and white • white only • pink only • red only
Check for understanding Eye color, hair color, and skin color are polygenic traits. Polygenic traits result from • recessive genes • many genes • codominant genes • epistaticgenes.
Check for understanding Identical twins who are raised apart can have differences that last a lifetime. This is evidence that • phenotype differences happen through epistaticgenes • genotype can change over time • environment and genotype interact to affect phenotype • codominanceaffects genotype
