More Human Genetics…Biology

Multiple Alleles

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

Multiple Alleles

Rh Factor• Another gene for proteins

on the membrane of blood cells

• You have them (+) or you don’t (-)

• (+) is dominant to (-)

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?

Sample Crosses1. 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

Sample Crosses2. 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

Sex-Linked Traits

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

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

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

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

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

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

Sample Crosses2. 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