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Blood Type and Sex Linked Inheritance

Blood Type and Sex Linked Inheritance. Multiple Alleles. Multiple alleles for a particular gene means that more than two alleles exist in the population. This does not mean that the gene in a particular individual possesses more than two alleles.

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Blood Type and Sex Linked Inheritance

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  1. Blood Type and Sex Linked Inheritance

  2. Multiple Alleles • Multiple alleles for a particular gene means that more than two alleles exist in the population. • This does not mean that the gene in a particular individual possesses more than two alleles. • An individual can only have a maximum of two of alleles, one maternal and one paternal, no matter how many alleles exist in the population. • Example: a population of dogs can have 5 alleles for coat color at one gene.

  3. The Classic Example of Codominanceand Multiple Alleles in Humans is BLOOD TYPE • Gene that controls ABO blood type codes for an enzyme that makes an antigen on blood cells. • Two alleles (IA and IB) are called “A” and “B” which are codominant. A and B can both be expressed on the same cell. • Third allele (i) is called “O”) and it is recessive to both A and B

  4. Possible Genotypes for Blood Types • If the Phenotype: A • Genotype(s): AA, Ao • If the Phenotype: B • Genotype(s): BB,Bo • If the Phenotype: AB • Genotype(s): AB • If the Phenotype: O • Genotype(s): oo

  5. Possible combinations of alleles

  6. A Real Problem:Mom is Type B, Dad is Type O … Baby is Type AB. Is this possible? Remember, when in doubt, heterozygous is more likely Bo oo • Cross: ____ X ____ mom B o o Bo oo SORRY! NOT POSSIBLE! o oo Bo

  7. Check your understanding • Could an AB father have a type O child? • Why? O is homozygous recessive. A or B would hide the o allele. Are the father’s alleles codominant or recessive?

  8. Sex Chromosomes:the 23rd pair in humans • All others (1-22) are called autosomes Boy Girl

  9. The Sex Chromosomes • The “X” Chromosome • Has essential genes • Can’t live without it! • Females have a 23rdpair = XX (one usually deactivated) • The “Y” Chromosome • Has fewgenes • Male 23rd pair = XY

  10. X Y X X XX XX XY XY What’s the probability of having a boy or girl? 50% 50%

  11. Some X-Linked Traits: • Hemophilia(missing clotting enzymes) • Bleeding disorders in which it takes a long time for the blood to clot. • Colorblindness • Defect in color vision • “Male-pattern” baldness • Most are recessive.

  12. A man with normal vision marries a colorblind woman. What is the probability that they will have a colorblind SON? Remember, Mom only shows if she is homozygous! XcXc XY • Cross: ____ X ____ mom Xc Xc Focus only on SONS (not daughters)! X XcX XcX 100% (2/2) SONS Y XcY XcY

  13. A hemophiliac man marries a healthy woman. What is the probability that they will have any hemophiliac children? • All sons healthy • All daughters carriers 0%

  14. Colorblindness • Red-green colorblindness- • Red and green appear to be the same. X-linked • Red-green affects: • 1 in 10 males in the US • 1 in 100 females in the US • Remember: Males have just one X chromosome. All X-linked alleles are expressed in males. • Other forms: • Total Colorblindness • Blue-Yellow colorblindness • Blue-yellow appears to be the same. It is autosomal Chromosomes 1 to 22

  15. What do you see?

  16. No.Va.CRIME SCENE INVESTIGATON • http://www.ansci.cornell.edu/usdagen/mult_alleles.html • Medline Plus, 2014, US National Library of Medicine, National Institutes of Health http://www.nlm.nih.gov/medlineplus/ency/article/002051.htm • Virtual Fruit Fly Lab, 2014, http://www.mhhe.com/biosci/genbio/virtual_labs/BL_15/BL_15.html

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