Human Genetics
Parts of Chapters 8 and 9
Sex Limited versus
Sex Influenced Inheritance
Sex Linkage
- Genes located on the sex
chromosomes are inherited in a ___________ fashion
- Y-linked genes are never
expressed in females
- X-linked recessive traits tend
to be expressed more often in males than females
- Males are said to be _____________ for X-linked genes
X-chromosome
Inactivation
- In female mammals, one X
chromosome in each cell is inactivated (called dosage compensation)
- This X inactivation accounts
for some differences between different tissues in some female mammals
(i.e. calico coat color in cats)
- Allows for both male and female
cells to be the same with respect to X-linked genes
Human Disorders
Caused by Changed in Chromosome Number
- Nondisjunction = failure of chromosomes (or chromatids) to disjoin during meiosis
- 1/2 of
the gametes will have an extra chromosome, and 1/2 of the gametes will be
miss a chromosome
- Results
in aneuploidy
- ____________________________
Human Aneuploidy
- Sex chromosome nondisjunction:
- XXY =
___________ syndrome (1:2,000)
- XXX =
___________ (1:1,000)
- XO =
___________ syndrome (1:5,000)
- XYY = ??? (1:2,000)
- Autosomal nondisjunction:
- Trisomy 21 =
___________ syndrome (1:700)
- Trisomy 18 =
Edward syndrome (1:5,000)
- Trisomy 13 = Patau syndrome (1:5,000)
Alterations of
Chromosome Structure
- ___________- missing a part of a
chromosome
- Partial
aneuploidy
- Can
lead to a variety of problems, depending upon the genes involved
- Chi-du-chat
caused by a partial deletion of chromosome 5
- ___________ -
caused by errors during replication or division
- ___________ - permanent
movement of part of a chromosome to another chromosome
- _____________- rearrangements within
chromosomes
Other Human
Disorders
- Recessive disorders
- Typically
due to a damaged gene
- Only
expressed when homozygous recessive
- Dominant disorders
- Not
very common, due to dominant effects
- Huntington’s
disease an exception: expressed late in life
- If an
individual has the disease, each child has a 50% chance of also having
the disease
Genetic Screening
- Carrier
recognition
- Can
test to see if both parents are carriers of a recessive disease
- Amniocentesis
- Tests
amniotic fluids surrounding fetus for chromosomal or biochemical
disorders
- Chorionic villus sampling (CVS)
- Similar
to amniocentesis but can be done earlier in pregnancy and provides
quicker results
Terminology: autosomes/sex
chromosomes, sex limited inheritance, sex influenced inheritance, sex linked
inheritance, X-linked genes, Y-linked genes, hemizygous,
criss-cross inheritance, X chromosome inactivation, nondisjunction, aneuploid,
deletion, duplication, translocation, inversion, carrier, amniocentesis, CVS