Lecture 2: DNA, Chromosomes and Genomes 2

Question 1

What is heterochromatin?

Answer 1

• very condensed chromatin
• late replicating and genetically inactive
• highly concentrated at centromeres and telomeres
• contains very few genes, those that are present are resistant to gene expression

Question 2

What is position effect?

Answer 2

Activity of a gene depends on position on chromosome. For example, if near heterochromatin, the gene may be silenced

Question 3

What is euchromatin?

Answer 3

less condensed chromatin that has gene expression

Question 4

What are the three types of histone modifications?

Answer 4

acetylation of lysines
mono, di, tri- methylation of lysines
phosphorylation of serines

Question 5

What happens in the acetylation of lysine?

Answer 5

loosens chromatin structure, added by histone acetyl tranferases (HATs); removed by histone deacetylase complexes (HDACs)

Question 6

What happens in the methylation of lysine?

Answer 6

tightens the chromatin structure, added by methyl transferases; removed by histone remethylases

Question 7

What is a variant histone protein?

Answer 7

synthesized during interphase and inserted into already formed chromatin
exits for each core histone except H4 and are less well conserved
Creates diversity

Question 8

What is the histone code read by?

Answer 8

The code reader complex, involves joint recognition of histone tail and covalent modifications

Question 9

What halts the spread of of chromatin modification?

Answer 9

barrier sequences

Question 10

What are types of barrier sequences?

Answer 10

physical or enzymatic

Question 11

What is the HS4 region?

Answer 11

protects the Beta globin locus from silencing, contains a cluster of histone acetylase binding sites

Question 12

What do centromere sequences consist of?

Answer 12

short repetitive DNA called alpha satellite DNA

Question 13

Centromeric heterochromatin is defined by ________, not ______

Answer 13

assembly of proteins, DNA sequence

Question 14

What happens to chromatin during gene transcription?

Answer 14

decondensation, “chromosome puffs”

Question 15

What happens to the location during gene expression?

Answer 15

actively transcribed genes extend out of its area on an extended chromosome loop

Question 16

True of false: mitotic chromosomes are highly condensed.

Answer 16

True

Question 17

What is the purpose of condensation?

Answer 17

disentanglement of sister chromatids to allow separation in cell division and protection of fragile DNA molecule as separation occurs

Question 18

What does condensin do?

Answer 18

use ATP hydrolysis to coil DNA molecules into chromatids

Question 19

What are homologues?

Answer 19

genes that are similar in both sequence and function due to common ancestry

Question 20

How do genomic changes occur?

Answer 20

occur as mistakes in DNA replication and repair

Question 21

What type of genomic changes can occur?

Answer 21

• base pair substitutions
• duplications
• deletions
• inversions
• translocations

Question 22

What are reasons for sequence conservation?

Answer 22

not having enough time for mutations since lineage separation
purifying selection

Question 23

What is purifying selection?

Answer 23

elimination of mutations that interfere with important gene functions

Question 24

What are pseudogenes?

Answer 24

duplicated gene that has become irreversibly inactive by multiple mutations

Question 25

Explain the evolution of the globin gene family

Answer 25

• duplication and mutation gave rise to beta and alpha genes
• translocation moved alpha to separate chromosomes
• further duplication and mutation resulted in more specialized beta molecules

Question 26

By how much do human sequences vary from one another?

Answer 26

0.1%

Question 27

what are SNPs?

Answer 27

• Single-nucleotide polymorphin.
• points in the genome where one group has one nucleotide and another group has another
• high variation rate

Question 28

What are CNVs?

Answer 28

• copy number variants

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