Download Human Inheritance

Human Inheritance
A. Pedigree
 A map or graphic representation of genetic inheritance
 Used to map genetic disorders
 Similar to a family tree
 Use symbols that are shaded, un-shaded or half shaded
 Lines between two symbols indicate marriage
 Lines above symbols indicate offspring or siblings
= unaffected male
= unaffected female
= affected female
= affected male
= female carrier
(heterozygous)
= male carrier
(heterozygous)
Parents
Siblings (children)
1st born
2nd born
B. Simple Recessive Heredity
 Most disorders are recessive
 Requires 2 recessive alleles (one from each parent)
1. Cystic Fibrosis
 Most common among white Americans
 Caused by a defective protein (mutation in DNA)
 Causes accumulation of thick mucous production in lungs and
digestive tract
2. Tay Sachs Disease
 Common among Amish and Jews of Eastern European ancestry
 Caused by the absence of an enzyme that breaks down fat in the
central nervous system (mutation in DNA where the code for this
enzyme is missing or incorrect)
 Causes fat to accumulate in the spinal cord and brain and
eventually crushes it
3. Phenylketonuria (PKU)
 Common in people of Norwegian and Swedish ancestry
 Caused by the absence of an enzyme that converts the amino
acid phenylalanine to tyrosine
 Phenylalanine accumulates and damages the CNS
 Infants with PKU that drink milk rich in phenylalanine will have
mental retardation
 Treated by altering the diet
C. Simple Dominant Heredity
 Only one allele that codes for the disorder is required
1. Huntington’s Disease
 Lethal disease that causes the breakdown of certain parts of the
brain
 Onset is not until ages 30-50
 If you don’t know your family history you may have had children
and passed the disease on to them by the time you are
diagnosed
D. Sex Determination
 Inherit one sex chromosome from each parent
XX = female
(one possible gamete = only X)
XY = male
(two possible gametes = X or Y)
*** It is the male sperm that determines the sex of the child
X
X
X
XX
XX
Y
XY
XY
50% chance of being female
50% chance of being male
1. Sex-linked Inheritance
 Traits determined by genes on the sex chromosomes
 Remember females have matching chromosomes (XX)
 Males do not have matching chromosomes (XY)
 Most of the traits are found on the X chromosome
a. Color Blindness
X X = normal female
X Y = normal male
X Xc = female carrier
Xc Y = color blind male
Xc Xc = color blind female
Q: What is the probability of having a female child with color
blindness with a normal mother and a father who is color blind?
X X
x
Xc Y
Xc
Y
X
X Xc
X Y
X
X Xc
X Y
A: 0%
b. Hemophilia X-linked disorder
 Causes problems with clotting the blood
 Severe bruising and difficulty stopping the bleeding
 Occurs more in males than females because males cannot
be carriers
X X = normal female
X Y = normal male
X XH = female carrier
XH Y = hemophiliac male
XH XH = hemophiliac female
E. Other Inheritance Disorders and Traits
1. Sickle-Cell Anemia
 When the red blood cells become sickle shaped
(crescent)
 The hemoglobin (protein) on the red bloods cells is not
produced and the RBC cannot carry oxygen
 This causes anemia and pain to the tissues
2. Blood Typing
Blood Types: A, B, AB, O
“I” or “i” is the allele used for blood type
3 alleles: IA, IB, i
Phenotype
Genotype
A
IA IA or
IA i
B
IB IB or
IB i
AB
IA IB
O
ii
Perform the following crosses
1. Heterozygous A x AB
2. Heterozygous A x Homozygous B
3. AB x AB
4. Heterozygous B x O
F. Testing for Genetic Disorders
1. Karyotype: picture used to identify chromosomal
abnormalities
 22 pairs of autosomal chromosomes (non-sex
chromosomes)
 1 pair of sex chromosomes