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

XXY

XYY

X0

0Y

Survivable with problems

Survivable with problems

Survivable with problems

Survivable with problems

Lethal

Non-disjunction in Sex Chromosomes

• Turner Syndrome --XO

• Klinefelter Syndrome—XXY

• Poly-X Females---XXX

• Jacobs Syndrome---XYY

• Mutation– a permanent genetic change.

• Chromosome mutation--change in chromosome structure.

• Types:– Inversion– Translocation– Deletion– Duplication

Changes in Chromosome Structure

Deletion

Duplication

Translocation

Inversion

WHAT’S HAPPENING??

• 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.

Sex-Linked Traits

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

• 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

Chapter Summary