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Genetics Problems with Incomplete Dominance and Codominance

Learn about incomplete dominance and codominance in genetics, solve related problems, and understand the concept of multiple alleles.

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Genetics Problems with Incomplete Dominance and Codominance

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  1. Fnord babies Do Now, 2/11 DO NOW!!! (HW check9.2-9.4, 9.6) Objective: Define incomplete dominance and codominance, and solve genetics problems involving both. Task: Period 2, teams 3, 4, & 7: select F2 flies to mate!!! In Fnords, orange (O) skin is dominant over blue skin (o). An orange fnord and a blue fnord mate, and produce 314 orange offspring and 307 blue offspring. What is the genotype of the orange parent? Two orange fnords mate, and they produce both orange and blue offspring. If they have 98 blue babies, about how many orange ones are there? Describe a cross you could make to figure out if one an orange fnord is homozygous dominant or heterozygous.

  2. FNORDS! • Oo • about 300 • cross with a blue fnord. If all offspring are orange, must have been a homozygote. Testcross

  3. Important Info from 9.1-9.2 • Generation titles P generation = parents F1 generation = offspring generation 1 (Latin filial = son) F2 generation = offspring generation 2 (from F1 self fertilization)

  4. Beyond Complete Dominance • In the crosses we looked at earlier, one allele (form of a gene) was completely dominant over the other. • Ex. Tt = phenotype “T” • Some traits are more complex however…

  5. Codominance For a trait that is codominant, heterozygotes display BOTH phenotypes. Look at the example of horses RR = Red fur rr = White fur Rr = Red AND White fur (roan)

  6. Codominance – Roan Horses

  7. Incomplete Dominance The heterozygote genotype has a blend of both possible homozygous phenotypes. rr RR Rr

  8. Pink flowers = RR’ • Since one allele isn’t really dominant, the non-functional allele (white in this example) is written with a capital letter and an apostrophe (i.e. R’, Q’, etc.) and called “R prime” for example.

  9. Flower Power • If you crossed two of the pink flowers on the previous slide, • What % would be pink? • What % would be red? • What % would be white? • What is the phenotype ratio?

  10. Do Now 2.11 OBJECTIVES: Complete objectives from yesterday Define, identify, and use Punnett squares to analyze genetic crosses for traits that are codominant and incompletely dominant. TASK: In Flibs, sex is determined by X and Y chromosomes just as it is in humans. Having feathers is a phenotype produced by a recessive allele on the X chromosome. What is the genotype of a male with feathers? What are the two possible genotypes of a female with no feathers? If a feathered female is crossed with a featherless male, what % of the female offspring will have feathers?

  11. Do Now 2.9 (HW check 9.18) • Objective: • Use a Punnett square to analyze genetic crosses involving traits that are sex-linked or multiallelic. • Task: • What are the three types of inheritance we’ve seen so far in class? • Write an example question about inheritance of a codominant or incompletely dominant trait.

  12. Shh! Don’t say a word!Write down what numbers (if any) you can read in each circle

  13. Are you color blind? • 4 Sex-Linked Traits: • 1. Normal Color Vision: A: 29,  B: 45,  C: --,  D: 26 • 2. Red-Green Color-Blind: A: 70,  B: --,  C: 5,  D: -- • 3. Red Color-blind: A: 70,  B: --,  C: 5,  D: 6 • 4. Green Color-Blind: A: 70,  B: --,  C: 5,  D: 2

  14. There are a LOT more color blind men than women!

  15. Try One – as sex-linkage example in notes • A female with normal vision that has 1 copy of a colorblindness gene (genotype X+ Xo) has children with a normal male (X+ Y). A. What % of their male children will be colorblind? B. What % of their female children will be colorblind? C. Do all colorblind women have a colorblind father? Explain

  16. 3 Different Alleles: Multiple Allele Traits The three alleles that determine blood type are represented as IA, IB, and i.

  17. Crosses A woman with blood type A has a baby with blood type O. The man she believes to be the father has the blood type AB. Is it possible the man is the father of the baby?

  18. He isn’t the Father!

  19. Multiple Allelic Traits Traits for which there are 3 or more alleles are said to be multiple allele traits, or multiallelic. Try the example cross on your notes

  20. Wrap up • Alleles can react in different ways, for different genes: • Codominance: both alleles expressed (roan horses) • Incomplete: heterozygote has blended phenotype (pink flowers) • Sex-linkage: males only get 1 copy! (colorblindness) • Multiple alleles: 3 or more alleles for 1 gene. (blood type)

  21. Homework • Syllabus reading • You should now be able to work on the 1,2, and 3-point problems on the “Classical Genetics Problem Set.”

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