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Explore inheritance patterns like incomplete dominance, codominance, and multiple alleles beyond Mendelian genetics. Investigate different phenotypes and possible genotypes based on ratios. Learn how blood types are determined by multiple alleles.
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Corn Investigation • Count the number of kernels that are: yellow & smooth, yellow & wrinkled, purple & smooth, purple & wrinkled. Reduce this ratio to lowest terms (it is okay to have decimals in your answer) • What type of inheritance are you examining? (Monohybrid or Dihybrid)? • Based on the ratio from Q1, what could the possible genotypes of the parents be? (hint: do not do a punnett square. Look at the ratio to help you figure out the parents) • You are modelling how Mendel recorded data. Is counting an effective way to collect data? Why? What is one experimental error that could have occurred? (Hint: counting wrong is not an error)
Beyond Mendel • Mendelian Genetics deals with inheritance patterns that show complete dominance • Meaning, the dominant allele completely masks (overpowers) the expression of the recessive allele • Are inheritance patterns in nature always this simple?
Incomplete Dominance • A situation where neither of the 2 alleles are dominant over the other. • Phenotype of heterozygote is a BLEND of the two alleles. • Alleles are written using a superscript letter (ex. CR = Red) • Example: snapdragons (see picture)
Codominance • Both alleles are dominant, and thus fully expressed in the heterozygote • Exhibited in a heterozygousindividual where both alleles of a gene are expressed, not blended. Sickle Cell Anemia (blood disease) Cow coat Impatien flowers
Examples of Co-Dominance Talk to me when there’s meat… meeow! Examples: • black cat x tan cat = Tabbycat (black and tan stripes) • Roan coat in horses (white and red hair)
Multiple Alleles • So far, the inheritance examples we have looked at only have 2 alleles • Example: Brown hair or blonde hair, brown eyes or blue eyes, etc. • Most traits in nature are controlled by more than 2 alleles, such as human blood groups
Multiple Alleles Recall:
Multiple Alleles Recall:
Multiple Alleles Recall:
Multiple Alleles • When more than 3 phenotypes are possible, then more than 2 alleles for that trait must exist in the population. • However, individuals have only two of those alleles. Why? • Because only one allele is inherited from each parent
Example of Multiple Alleles • The ABO system of human blood type involves three alleles (IA, IB, and i). • IA and IB – co-dominant, where “i” is recessive • As a result, there are four possible phenotypes or blood types: A, B, AB, and O.
What do the Alleles Code For? • The blood types differ due to the molecules that are present on the outside of the red blood cells (antigens) • Antigens act as recognition factors for our immune system
Type A Type AB Type B Type O What do the Alleles Code For? Both A & B No antigens
What do the Alleles Code For? • When white blood cells do not recognize the antigen, it considers the cell an invader and produces antibodies to attack that cell • This is why receiving an incorrect blood type will cause agglutination (clumping).
Human Blood Groups: Multiple Alleles AND Codominance • Human blood types are controlled by a single gene (expressed as an antigen: protein on surface of red blood cell)
Example • If a man has type AB blood and his wife has type A blood (heterozygous), what are the possible blood types of their children?
