DIFFICULT CONCEPTS FOR ME

Question 1

Classes of repetitive DNAs: (2)

Answer 1

Tandem repeats, i.e. “satellite DNAs”

Dispersed repetitive elements

Question 2

Types of human DNA variation (4)

Answer 2

Insertion-deletion polymorphisms (indels):
Single Nucleotide Polymorphisms (SNPs)
Copy number variations (CNVs)
Others: chromosomal or larger scale variations, rearrangements, translocations, etc.

Question 3

Tandem repeats, i.e. “satellite DNAs”

Answer 3

used as the basis for cytogenetic banding

“α-satellite” repeats found near centromeric region of all human chromosomes

Question 4

Dispersed repetitive elements

Answer 4

Alu SINEs: Short Interspersed repetitive Elements)

L1 LINES: Long Interspersed repetitive Elements)

=====Retrotransposition===

Repeats may facilitate aberrant recombination events

!!!Non-allelic homologous recombination (NAHR)!!!

Question 5

During what phase of meiosis does crossover occur?

Answer 5

Prophase 1. Homologous chromosomes line up to form bivalents and segregate independently during Meiosis 1.

[Reciprocal recombination events occurring at this stage generate physical links between homologs. These attachments, or crossovers, are also known as chiasmata.

Meiosis I is the most error-prone step of the process, and chromosome nondisjunction at this stage is the most frequent mutational mechanism in humans.]

Question 6

Translocation, Robertsonian for down syndrome?

Answer 6

46,XX,der(14;21)(q10;q10),+21

A patient with translocation Down syndrome, carrying one normal chromosome 14 and two normal chromosome 21s in addition to a Robertsonian translocation chromosome (14q-21q); der = derivative chromosome.

Question 7

A small percentage of Down syndrome patients have the 21q21q isochromosome e.g. ______. Although this is a rare rearrangement, all the gametes of a phenotypically normal carrier of this isochromosome _____

Answer 7

46,XX, i(21)(21q21q);

must contain either the 21q21q chromosome (giving 3 copies of chromosome 21 after fertilization), or gametes that lack chromosome 21, resulting in monosomy (inviability) upon fertilization. Thus, 100% of the viable offspring are abnormal.

Question 8

At what phase of the cell cycle does inheritance of a chromatin state begin?

Answer 8

S phase during DNA replication