Lecture 2

Question 1

Compare Heterochromatin with Euchromatin and where are they commonly found?

Answer 1

Heterochromatin is tightly condensed and therefore less genetically active than Euchromatin

Heterochromatin is often found near centromeres and telomeres.

Question 2

Compare Heterochromatin and Euchromatin in terms of when they are replicated

Answer 2

Heterochromatin is thought to replicate later than Euchromatin

Question 3

Describe position effect

Answer 3

describes the relationship between a gene’s position on a chromosome and it’s level of genetic activity

the closer a gene is to heterochromatin, the less genetically active it usually is

Question 4

Define Position Effect Variegation

Answer 4

breakage events that bring heterochromatin near active gene sites and consequently silence the expression of those active genes.

Question 5

Where to histone modifications occur?

Answer 5

to the histone tails of any of the octamer subunits, or less commonly, directly to the histone itself

Question 6

Histone Modifications:

Acetylation

Answer 6

loosens the histone and the histone tails

increases genetic action by making the DNA more accessible

Question 7

Histone Modifications:

Methylation

Answer 7

(can occur in mono-,di-, or tri- forms): tightens the histone structure

Question 8

Histone Modifications:

Phosphorylation

Answer 8

causes gene activation by loosening the structure

Question 9

Define CENP-A

Answer 9

a Variant Histone protein for the H3 subunit, that is commonly found at Centromeres

Question 10

What is involved with Histone code reading?

Answer 10

Code Reader Complexes: read the histone code

Code Reader-Writer Complexes: contain ATPase (to consume ATP) used to read and remodel (condense or decondense) stretches of chromatin based on their histone code

Barrier Sequences: are responsible for the containment of the remodeling performed by histone reader-writer complexes

Question 11

What do physical barrier, barrier proteins do?

Answer 11

essentially “box out” areas that the cell does not want remodeled

Question 12

Explain an example of an Enzymatic barrier to chromatin remodeling

Answer 12

Enzymatic barriers such as Beta globin locus that contains a cluster of histone acetylase binding sites over the stretch of chromatin that codes for RBC’s

This keeps RBC chromatin accessible so that it can constantly code for RBC’s (we always need more of these)

Question 13

Describe the inheritance of Chromatin structures

Answer 13

• H3 and H4 histones stay complexed with DNA during the replication process while H2A and H2B float off, and then return later in the replication process, at the DNA replication fork

The H3 and H4 histones staying complexed helps to be sure that the histones are assembled in the correct position during the DNA replication process

Question 14

What are Condensins?

Answer 14

proteins that consume ATP and aid in the untanglement of sister chromatids/condensation that is needed to allow for the separation of chromatids during cell division

Major component during metaphase

Question 15

Define Poltene Chromosomes

Answer 15

“bundle of straw-looking” chromosomes that form “chromatin puffs” during gene expression

Question 16

Define Chromosomes Loops

Answer 16

occur during genetic expression in order to be more easily expressed

Question 17

Describe how genomes evolve

Answer 17

Single nucleotide polymorphisms (SNP’s) can cause high rates of genetic variation

Question 18

Define Copy Number Variants (CNV’s)

Answer 18

the presence of many duplications and deletions of large blocks of DNA

Question 19

How to genomic changes occur?

Answer 19

Occur as mistakes in DNA replication and repair but only very rarely and occur in 2 ways

1. Base pair substitutions
2. Large scale rearrangements

Question 20

Duplications, Deletions, Inversions, and Translocations are all examples of what?

Answer 20

Large scale rearrangements of DNA sequences

Question 21

What are the reasons for sequence conservation?

Answer 21

Purifying selection: the process by which mutations are eliminated from the gene pool when they interfere with important genetic functions

also, the large amount of time that it takes for mutations to occur

Question 22

How does gene duplication occur?

Answer 22

Little selective pressure to maintain mutation free can create Pseudogenes or copies of genes that have become irreversibly inactivated by multiple mutations

Question 23

After Pseudogenes occur, what can occur that causes mutations?

Answer 23

Divergence: where one of the duplicate genes mutates and eventually gets expressed