Chromosomes

Chromosomes

Chromosome and its 3 essential parts:

Primarily consist of DNA and Protein distinguished by size and shape:

• Telomeres

• Origins of replication sites

• Centromere

Six

• P short arm

• q long arm

• Telomeres

• Centromere

• Heterochromatin (dark)

• Euchromatin (light)

Centromere

• Largest constriction of the chromosomes and where spindle fibers attached

• Bases that form the centromere are repeats of a 171-base DNA SEQUENCE

• Replicated at the end of S PHASE.

  • Facilitated by centromere protein A (CENP-A) is passed to next generation

    • Example of an EPIGENETIC CHANGE

Subtelomere

Chromosome region between the centromere and telomeres

• Consist of 8000 to 300,000 bases

• Near telomere the repeats are similar to the telomere sequence

  • Contains at least 500 protein encoding genes

  • About 50% are multigene families that include pseudogenes

Karyotype

A lab test where you need to get the chromosome of the cell of the patient to assess its quality.

• A chromosome chart

• Major clinical tool

  • That displays chromosomes arranged by size and structure

Humans have _____ chromosomes types

24 chromosomes

Germ cell or sex chromosomes are _______ and _______.

X and Y.

Autosomes are numbered _____ by size.

1-22

Karyotype benefits:

• Confirms clinical diagnosis

• Reveal effects of environmental toxins (abnormal chromosome due to triggers)

• Clarify evolutionary relationships

Centromere positions:

• Metacentric

• Submetacentric

• Acrocentric

• Telocentric

In visualizing chromosomes, tissue is obtained from person: what are those:

1. Fetal tissue

   1. Amniocentesis

   2. Chorionic villi sampling

   3. Fetal cell sorting

   4. Chromosome microarray analysis

2. Adult tissue

   1. White blood cells

   2. Skin-like cells from cheek swab

Generally, in karyotyping, once chromosomes are extracted what is done next to visualize chromosomes?

Stained with a combination of dyes and DNA probes.

Amniocentesis

A procedure to get a sample of amniotic fluid

• Detects about 1000 of the more than 5000 known chromosomal and biochemical problems

• Ultrasound is used to follow needle’s movement

Chorionic Villus Sampling

• 10th-12th week of pregnancy (Early, 3 months of pregnancy)

• Chorionic villi, found in the placental tissue. (cells of the chorion are the samples)

Provide earlier results than amniocentesis but does not detect metabolic problems

• Has GREATER RISK OF SPONTANEOUS ABORTIONS

Flourescence In Situ Hybrydrization (FISH)

DNA PROBES to bind the type of chromosome, they need to paired or targeted.

• DNA PROBE (reagents) labeled with flourescing dye bind complementary DNA

• Flourescent dots correspond to three copies for chromosome 21

46 chromosomes: 23 pairs. _____ pair of autosome chromosome, ______ pair of sex chromosomes.

22 pairs, and 1 pair.

Ideogram

schematic chromosome map

• Study the individual regions or bands located on the long arm (q) and the short arm (p)

Karyotype may be abnornal in ______ and _________?

• Number

• Structure

Polyploidy

Extra chromosome set

Aneuploidy

An extra or missing chromosome

Monosomy

One chromosome is absent

Trisomy

One chromosome is extra

Deletion

A part of chromosome is missing.

Duplication

Part of a chromosome is present twice.

Translocation

Two chromosomes join the long arms or exchange parts.

Inversion

A segment of chromosome is reversed.

Isochromosome

A chromosome with identical arms.

Ring chromosome

A chromosome that forms a ring due to deletion in telomeres, which causes ends to adhere.

Chromothripsis

One or more chromosome shatters.

Maternal serum markers for Trisomy 21

Cell - Free DNA testing

This looks at the maternal blood pieces of DNA from the fetus.

• up to 20% of these pieces comes from the placenta, and thus represents the fetal genome.

• Testing DNA can detect certain fetal chromosomal abnormalities like some of the trisomy conditions.

• The test can be performed at 10 weeks into pregnancy.

Indirect Detection of chromosomes:

1. Maternal Serum Screening

2. Cell - Free DNA testing