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KCI 2014

KCI 2014. BEYOND MENDELIAN GENETICS Conditions that Mendel didn’t explore: Incomplete Dominance Co-dominance Multiple Alleles Polygenic Traits Lethal gene. Limitations of Mendelian genetics.

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KCI 2014

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  1. KCI 2014 BEYOND MENDELIAN GENETICSConditions that Mendel didn’t explore:Incomplete DominanceCo-dominanceMultiple AllelesPolygenic TraitsLethal gene

  2. Limitations of Mendelian genetics • Some genes are NOT independently assorted simply because they are too close to each other on a chromosome • some alleles are incompletely dominant • some genes are sex-linked • A single trait can be controlled by many genes which can have multiple alleles

  3. Incomplete dominance Flower color of snapdragons • A condition in which neither allele for a gene completely conceals the presence of the other; it results in intermediate expression of trait 3 phenotypes are observed in F2 in a 1:2(blended traits):1 ratio

  4. Incomplete dominance • However, the alleles of flower color do segregate according to Mendel’s law of independent assortment • In human, traits showing incomplete dominance:

  5. How to represent incomplete dominance? • Use superscripts rather than upper-case and lower-case letters since neither allele is dominant over the other • Eg. Snapdragon flower colour: both alleles affect the colour of flower C • 2 alleles are therefore CR (red) and CW (white)

  6. https://www.youtube.com/watch?v=R4-c3hUhhyc Incomplete dom. Sickle cell disease in humans. Trait concerned: Shape of blood cells Hb: letter chosen to represent hemoglobin HbAHbA: normal biconcave disk HbSHbS: sickle cell S shape HbAHbS sickle cell trait (some normal and some sickle blood cells under prolonged low O2 condition)  resistant to malaria giving the individuals a heterozygous advantage

  7. If both parents have sickle cell trait (heterozygous), what is the chance of their offspring having sickle cell anemia? P: HbAHbS xHbAHbS F1: Answer: 25% chance their offspring will have sickle cell anemia (HbSHbS)

  8. Codominance • Is the condition in which both alleles for a trait are equally expressed in a heterozygousoffspring; both alleles are dominant E.g a. Shorthorn roan cow Cattle can be red (HRHR = all red hairs), white (HWHW = all white hairs), or roan (HRHW = red & white hairs together) b. Human AB blood type (two types of protein ("A" & "B") appear together on the surface of blood cells.)

  9. Codominance Correct the letter HR,not Hr as expressed in your textbook

  10. What’s the difference between incomplete dominance and codominance? • E.g. a. Incomplete dominance: - Both alleles are partially expressed - Offspring shows a third phenotype that is something between the parents’ phenotypes (i.e. a blend) b. Co-dominance: - Both alleles are fully expressed - Offspring shows a third phenotype that is completely different from both the parents’ phenotype Correct the letter r to R in this co-dominance cross 

  11. Multiple alleles • So far we’ve studied traits controlled by one gene with two alleles • An individual has only 2 alleles for a gene but many different alleles for a gene can exist within a population • A gene with more than 2 alleles is said to have multiple alleles

  12. Reminder

  13. Human blood types: example of both codominance and dominance • One single gene determine a person’s blood type: A, B or O • This gene is designated as I and have 3 alleles that code for antigen proteins attached to the RBC’s membrane Possible alleles from a female Possible alleles from a male RECAP: http://wps.aw.com/bc_goodenough_boh_3/104/26722/6840887.cw/content/index.html

  14. Multiple Alleles (Cont.) – Rabbit Coat

  15. P: cchc x Cch F1: Genotypic Ratios: 1 Ccch: 1Cc : 1 cchch: 1 chc Phenotypic Ratios: 2 dark grey: 1 light grey: 1 Himalayan Predict the genotypic ratio and phenotypic ratio of a cross between a heterozygous Chinchilla (cchc) with a heterozygous dark grey (Cch). One trait (i.e. rabbit coat color) is influenced by multiple alleles

  16. Complete attached practice problems on incomplete-, co-dominance and multiple allelesTaking up Practice problem

  17. Incomplete dominance practice problem SpongeBob loves growing flowers for his pal Sandy! Her favorite flowers, Poofkins, are found in red, blue, and purple. 1. Write the correct genotype for each color if R represents a red gene and B represents a blue gene. Red - Blue - Purple - 2. What would happen if SpongeBob crossed a Poofkin with red flowers with a Poofkin with blue flowers. (a) Give the genotypes and phenotypes for the offspring. (b) How many of the plants would have red flowers? _____% (c) How many of the plants would have purple flowers? _____ % (d) How many of the plants would have blue flowers? _____ % 3. What would happen if SpongeBob crossed two Poofkins with purple flowers? (a) Give the genotypes and phenotypes for the offspring. (b) How many of the plants would have red flowers? _____% (c) How many of the plants would have purple flowers? _____ % (d) How many of the plants would have blue flowers? _____ %

  18. Codominance practice problem 1. In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette. • a. What is the genotype for black chickens? ____ • b. What is the genotype for white chickens? ____ • c. What is the genotype for erminette chickens? ____ 2. If two erminette chickens were crossed, what is the probability that: a. They would have a black chick? ____% b. They would have a white chick? ____%

  19. 3. In a certain fish, blue scales and red scales are codominant. When a fish has the genotype B R, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales.  Step 1: Determine the genotypes of the parents CB CR = CB CB = CR CR =

  20. Multiple alleles practice problem 1. In the 1950’s, a young woman sued film star/director Charlie Chaplin for parental support of her illegitimate child. Charlie Chaplin’s blood type was already on record as type AB. The mother of the child had type A and her son had type O blood. • Complete a Punnett square for the possible cross of Charlie and the mother. b. The judge ruled in favor of the mother and ordered Charlie Chaplin to pay child support costs of the child. Was the judge correct in his decision based on blood typing evidence? Explain why or why not. *Use Punnett squares to support your answer.

  21. Alien Genotyping: 2. In these aliens, horns are controlled by three allelles • One center horn (A) is codominant with two horns (B). If an alien inherits both alleles (AB), then the alien has 3 horns. A recessive allele (O) results in an alien have no horns. Match the genotype to each of the pictures below.

  22. Incomplete dom. Show: a. Pink x Red b. Pink x Pink c. White x White

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