Transcript 11.3 Human Heredity

Human Heredity
11.3
Human Chromosomes
Humans have 46 chromosomes
Occurs in 23 pairs
22 pairs are autosomes
2 of the 46 are sex-determining chromosomes
(X and Y)
XX=Female, XY=Male
Picture of chromosomes=karyotype
Doctors use to determine sex of baby and
genetic abnormalities
Karyotype Studies
Karyotype—micrograph in which the pairs
of homologous chromosomes are arranged
in decreasing size.
Images of chromosomes stained during
metaphase
SAMPLE KARYOTYPE
Nondisjunction
Cell division during which sister
chromatids fail to separate properly
Example: Down syndrome – person has
an extra copy of chromosome 21
Pedigree
Chart that shows relationships within
families often used to trace lineage of a
disease/disorder
Circle=Female
Square=Male
Shaded=Affected
__ marriage
I children
Human Genes
Autosomal Recessive Disorders-caused
by 2 recessive alleles present (ex: PKU,
Tay Sach’s, CF)
Autosomal Dominant Disorders-only
one allele present causes affliction (ex:
dwarfism, Huntington’s Disease)
Codominant Alleles-Sickle Cell
Recessive Disorders
A.Cystic fibrosis: Homozygous recessives
(cc) have cystic fibrosis - body cannot make
needed chloride channel, high concentrations
of extracellular chloride causes mucous to
build up, infections, pneumonia. Diet,
antibiotics and treatment can extend life to 25
years or more.
B.Tay-Sachs: Enzyme that breaks down
brain lipids is non-functional in homozygous
recessives (tt). Buildup of lipids causes death
by age 2-3
Dominant Disorders
*Achondroplasia (dwarfism): AA =
Homozygous dominant is lethal - fatal
(spontaneous abortion of fetus). Aa =
dwarfism. aa = no dwarfism. 99.96% of
all people in the world are homozygous
recessive (aa)
Dominant Disorders
B. Polydactyly (extra fingers or toes):
PP or Pp = extra digits, aa = 5 digits.
98% of all people in the world are
homozygous recessive (pp)
Co Dominant Alleles
ss= sickle cell anemia (misshapen
Sickle Cell: many believe sickle cell
anemia co evolved with malaria
cells lead to death)
SS= normal red cells, healthy
Ss= not enough sickle cells to kill and
resistant to malaria! (body destroys the
sickle cells and the parasite)