Transcript complex inheritance of human traits

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