COMPLEX INHERITANCE OF HUMAN TRAITS Chapter 12.3

CODOMINANCE IN HUMANS SICKLE CELL ANEMIA If homozygous, red blood cells take on a “sickle” shape If heterozygous, person will produce both normal and sickle shaped red blood cells Sickle cell cause slow blood flow Block small vessels Result in tissue damage and pain

MULTIPLE ALLELES AND BLOOD TYPE ABO BLOOD GROUP Type A, Type B, Type AB, Type O Controlled by 3 alleles IA, IB, I Blood typing is necessary for blood transfusions So the body doesn’t “reject” the blood Blood typing is also used to determine paternity of a child

SEX-LINKED HUMAN TRAITS Most genes are located on the X chromosome X-LINKED RECESSIVE TRAITS Red-green color blindness hemophilia

Red-Green Color Blindness Caused by inheritance of a recessive allele on the X chromosome People can’t identify red and green traffic lights by color

Hemophilia X linked recessive disorder that causes your blood to not be able to clot Cuts take a long time to stop bleeding Females need 2 recessive alleles to show trait, males only need 1

POLYGENIC INHERITANCE IN HUMANS Skin Color

CHANGES IN CHROMOSOME NUMBER ABNORMAL NUMBER OF AUTOSOMES Extra autosomes = “trisomy” Instead of having 46 chromosomes, they would have 47 Results from “nondisjunction” during meiosis Failure of homologous chromosomes to separate Karyotype: chart of chromosome pairs used to identify unusual chromosome numbers in a cell

Down Syndrome: Trisomy 21 The ONLY autosomal trisomy which doesn’t result in death 3rd chromosome present in 21st pair Incidence of this increases in mothers that give birth over age 40

Abnormal # of Sex Chromosomes XO (Missing X chromosome) XXX, XXY, or XYY As long as there is 1 Y chromosome, the child will be a male Extra 23rd pair chromosomes People lead normal lives, however, they can’t have children and some have varying degrees of mental retardation