COMPLEX INHERITANCE COMPLEX INHERITANCE OF HUMAN TRAITSOF HUMAN TRAITS

Chapter 12.3

CODOMINANCE IN HUMANSCODOMINANCE IN HUMANSSICKLE 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 MULTIPLE ALLELES AND BLOOD TYPETYPE

ABO BLOOD GROUP◦Type A, Type B, Type AB, Type O◦Controlled by 3 alleles

IA, IB, IBlood 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 TRAITSSEX-LINKED HUMAN TRAITSMost genes are located on the X

chromosomeX-LINKED RECESSIVE TRAITS

◦Red-green color blindness◦hemophilia

Red-Green Color BlindnessRed-Green Color BlindnessCaused by inheritance of a recessive

allele on the X chromosomePeople can’t identify red and green traffic

lights by color

HemophiliaHemophiliaX 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 POLYGENIC INHERITANCE IN HUMANSHUMANS

Skin Color

CHANGES IN CHROMOSOME CHANGES IN CHROMOSOME NUMBERNUMBER

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 21Down Syndrome: Trisomy 21The ONLY autosomal trisomy which

doesn’t result in death3rd chromosome present in 21st pairIncidence of this increases in mothers that

give birth over age 40

Abnormal # of Sex ChromosomesAbnormal # of Sex Chromosomes

XO (Missing X chromosome)XXX, XXY, or XYYAs long as there is 1 Y chromosome, the

child will be a maleExtra 23rd pair chromosomes

◦People lead normal lives, however, they can’t have children and some have varying degrees of mental retardation