Chapter 6: Cytogenetics Flashcards
chromosome structure
a long arm (q) and short arm (p), joined by the centromere
why are there telomeres on the ends of each chromosomal arm?
it prevents chromosomes from sticking together and it shortens after cell division due to aging
what are the types of chromosomes?
- Chromosomes pair assigned numbers
- Chromosomes are identified by size, centromere location, and banding pattern
Autosomes vs Sex chromosomes
Autosomes are chromosomes other than the sex ones (1-22) and it’s not involved in sex determination. Females have homologous sex chromosomes (XX) and males have non-homologous (XY). The X and Y differ in shape and size.
How does the X and Y Chromosomes determine sex in humans?
Children receive an X from their mom, but either an X or Y chromosome from their dad
The X chromosome vs Y chromosome
The X chromosome is much larger and contains more genes than the Y. The X contains genes needed by both sexes while the Y contains mostly genes necessary for male development.
Sex Determining Region of Y
a single gene that is the primary determinant of maleness
Chromosome Banding Pattern
The staining of chromosomes produce a distinctive chromosome-specific banding pattern. Also the overall shape helps identify the specific chromosome #
Karyotype
Chromosomes are arranged in pairs according to size, banding pattern, and centromere location
What does karyotypes reveal?
- Total # of chromosomes present
- sex of an individual
- presence or absence of individual chromosomes
- possibility of structural abnormalities
Prenatal chromosomal analysis
analysis of fetal cells from maternal blood
Euploid
The normal diploid (2n) and haploid (n) number of chromosomes in human cells
Polyploidy
An increase in the # of chromosome sets
Triploidy
- most common
- fatal within a month
- most common is 69, XYY; resulting from dispermy
Aneuploidy
Changes in chromosome #s involving less than the duplication of a whole chromosome set
- Often the gain/loss of a single chromosome
Trisomy 18
-47+18
-Parental age is a common risk factor
- lethal within 2-4 months of age
What is the leading cause of childhood intellectual disability?
Trisomy 21: Down Syndrome (47, +21)
What is the cause of autosomal aneuploidy?
Most often due to non disjunction during meiosis
what is the difference between nondisjunction in meiosis?
in meiosis 1, its failure of homologous chromosomes to separate. in meiosis 2, it’s failure of sister chromatids to separate.
How is maternal age a risk factor?
At age 40, a mother’s oocytes have been in meiosis for more than 40 years so the chance for intercellular factors to cause damage to oocytes increases.
What is turner’s syndrome?
- 45, X (monosomy of x chromosome)
- only viable monosomy in humans
- result from nondisjunction
Klinefelter syndrome
- 46, XXY
- both maternal and paternal age
increased atypical characteristics
XYY syndrome
-47, XYY
Translocation
- two non homologous chromosomes exchange parts
- no info is lost, just shuffled around
- sometimes no effect and sometimes can cause cancer
inversion
- section of chromosome is flipped and reinserted into the same chromosome
