Patterns of Chromosome
Inheritance
Chapter 24
Karyotyping
• Karyotype
– Size-ordered chart of the metaphase
chromosomes of an individual cell
• Chromosomal aberration
– A mutation that is large enough to see under a
light microscope
Amniocentesis
Chorionic villi sampling
Normal male karyotype
Down syndrome karyotype
Changes in Chromosome Number
• Nondisjunction
• Result after fertilization:
– Trisomy
– Monosomy
Nondisjunction in Meiosis I
Nondisjunction in Meiosis II
Down Syndrome
Changes in Sex Chromosome Number
• Y chromosome-determines maleness.
• SRY gene produces a testis-determining
factor
• Caused by non-disjunction
Non-disjunction in Sex Chromosomes
Y chromosome-determines maleness.
Results of non-disjunction?:
XXX
Survivable with problems
XXY
Survivable with problems
XYY
Survivable with problems
X0
Survivable with problems
0Y
Lethal
•
•
•
•
Non-disjunction in Sex
Chromosomes
Turner Syndrome --XO
Klinefelter Syndrome—XXY
Poly-X Females---XXX
Jacobs Syndrome---XYY
Changes in Chromosome Structure
• Mutation– a permanent genetic
change.
• Chromosome mutation--change in
chromosome structure.
• Types:
– Inversion
– Translocation
– Deletion
– Duplication
Deletion
Duplication
Translocation
Inversion
WHAT’S HAPPENING??
Sex-Linked Traits
• Traits controlled by genes on the X or Y
chromosomes are sex-linked although
most are unrelated to gender.
• An allele on the X chromosome that is in
the region where the Y chromosome has
no alleles will express even if recessive; it
is termed X-linked.
• A female would have to have two
recessive genes to express the trait; a
male would only need one.
X-Linked Alleles
• The key for an X-linked problem shows the
allele attached to the X as in:
• XB = normal vision
• Xb = color blindness.
• Females with the genotype XBXb are
carriers because they appear to be normal
but each son has a 50% chance of being
color blind depending on which allele the
son receives.
• XbXb and XbY are both colorblind.
Cross involving an X-linked allele
X-linked recessive pedigree chart
X-Linked Disorders
• Red-green color blindness
• Muscular dystrophy.
• Hemophilia.
http://perth.uwlax.edu/faculty/howard/BIO101/DNA&translation/sld002.htm
Diana
http://brie.medlabscience.med.ualberta.ca/de/genetics/70gen-hemophil.html
Chapter Summary
• Humans - 22 pairs of autosomes and one
pair of sex chromosomes
• Abnormalities of chromosome number or
composition.
• Males - XY
• Females -XX.
• Chromosomal mutations
• Sex-linked traits