Adva nced Genetics: Multiple Alleles & Sex-Linked Traits

1. Advanced Genetics: Multiple Alleles & Sex-Linked Traits Biology Honors 8.5, 16.7 (blood types) 8.6 (sex-linked traits)

2. Multiple Alleles

3. Multiple Alleles • Traits are the result of more than 3 or more types of alleles • Example: blood typing • There are 3 different alleles for blood type (A, B, & O) • A is dominant to O • B is dominant to O • A and B are codominant

4. Multiple Alleles

5. Rh Factor • Another gene for proteins on the membrane of blood cells • You have them (+) or you don’t (-) • (+) is dominant to (-)

6. Blood Transfusions • Type A = A antigens (proteins) • Type B = B antigens • Type AB = A & B antigens • Type O = No antigens • Blood can only be transferred to a body of a person who's immune system will "recognize" it. • O is the universal donor • O blood has no antigens are that are foreign to the body • AB is the universal recipient • Person with AB blood has both the A and B antigens already in the body • Rh factor counts too! • (+) can receive (+) or (-) • (-) can only receive (-) • Ever see ER shows where doctors call for O neg. blood?

7. Sample Crosses 1. Cross a man with type AB blood with a woman who is heterozygous for type A blood • AB x AO • Geno: ¼ AA; ¼ AB; ¼ AO; 1/4 BO • Pheno: ½ type A; ¼ type B; ¼ type AB

8. Sample Crosses 2. Cross a man who is heterozygous for type A blood with a woman who is heterozygous for type B blood. • AO x BO • Geno: ¼ AB; ¼ BO; ¼ AO; ¼ OO • Pheno: ¼ type AB; ¼ type B; ¼ type A; ¼ type O

9. Sex-Linked Traits

10. Sex-linked Traits • A gene that is found only on the X chromosome and not the Y chromosome • Examples: • Colorblindness • Hemophilia • Duchenne Muscular Dystrophy • Male Pattern Baldness Female Male

11. Sex-linked Traits • More common in men because they only have one X chromosome • Females need to have the gene on both X’s to have the trait • Females that are heterozygous for the trait are carriers • Carriers appear normal but can pass the trait to their offspring

12. Colorblindness • Recessive gene (b) on X chromosome • Condition in which certain colors cannot be distinguished • Red/Green color blindness is most common (about 99%) • Causes problems in distinguishing reds and greens • No treatment • Life is normal

13. Hemophilia • Recessive gene (h) on the X chromosome • Bleeding disorder in which the blood does not clot normally • Persons with hemophilia may bleed for a longer time than others after an injury or accident • They also may bleed internally, especially in the joints • Live life cautiously, receive treatments to help blood clot normally

14. Duchenne Muscular Dystrophy • Recessive gene (d) on the X chromosome • Rapidly-worsening muscle weakness that starts in the legs and pelvis, and later affects the whole body • No cure • Treatment is aimed at control of symptoms to maximize the quality of life • Death usually occurs by age 25

15. Sample Crosses 1. Cross a normal man with a woman who is a carrier for hemophilia • XHY x XHXh • Geno: ¼ XHXH; ¼ XHXh; ¼ XHY; ¼ XhY • Pheno: ½ females will be normal; ½ females will be carriers; ½ males will be normal; ½ males will be hemophiliacs

16. Sample Crosses 2. Cross a colorblind male with a female who is a carrier for colorblindness. • XbY x XBXb • Geno: ¼ XBXb; ¼ XbXb; ¼ XBY; ¼ XbY • Pheno: ½ females will be colorblind; ½ females will be carriers; ½ males will be normal; ½ males will be colorblind