DNA to Genes to Chromosomes (Part 2)

Question 1

Minisatellite extragenic DNA is further divided into what subcategories?

Answer 1

• Telomeric

- Hypervariable

Question 2

What are the characteristics of Telomeric minisatellite extragenic DNA?

Answer 2

-short (~6 nt) repeats found at the end of chromosome (telomeres) - Added by telomerases after DNA replication and necessary to prevent shortening of chromosomes

Question 3

What are the characteristics of hypervariable minisatellite extragenic DNA?

Answer 3

-Short sequences (15-100 nt) repeated a variable number of times - Found in and around genes and were previously used for genetic fingerprinting (VNTR)

Question 4

What are the characteristics of microsatellite tandem repeat extragenic DNA?

Answer 4

• Very short sequences, usually 2 nucleotides long (e.g. CACACA) but can be 3 or 4, repeated 5-50x
• Highly variable in number of repeats so often used in genetic fingerprinting, linkage studies (STR: short tandem repeat )
• Trinucleotide repeat expansion associated with a number of disease 12 syndromes

Question 5

Highly repeated Interspersed Repetitive Sequences, the other type of Extragenic DNA besides Tandem Repeat, are categories into what?

Answer 5

• Short interspersed nuclear elements (SINEs)

- Long Interspersed Nuclear Elements (LINEs ~6000 base pairs)

Question 6

What are short interspersed nuclear elements (SINEs) and what are their characteristics?

Answer 6

• short sequences of <500 bp that are found up 1,500,000 times in the genome - make up about ~10% of the human genome
• appear to be “normal” RNAs that were converted to DNA by reverse transcriptase and were reinserted into the genome.

Question 7

What are the most common SINEs in humans?

Answer 7

Alu elements

Question 8

LINEs are able to make RNA (T/F)

Answer 8

True!!!

Question 9

What codes for the enzyme Reverse Transcriptase?

Answer 9

Long Interspersed Nuclear Elements

Question 10

How are LINEs capable of copying themselves and enlarging the genome?

Answer 10

Reverse transcriptase make a DNA copy of the LINE or SINE mRNA that can be integrated into the genome at a new site

Question 11

LINEs and SINEs are suspected to be responsible for what?

Answer 11

Many of the mutations that have arisen due to unequal crossover during meiosis

Question 12

What are pseudogenes?

Answer 12

Sequences that look like real genes but are not functional (no protein product).

Question 13

What is important to know about Mitochondrial (non-nuclear) DNA?

Answer 13

• Maternally inherited in humans (all mitochondria come from the cytoplasm of the oocyte)
• Mitochondrial disorders are only passed through maternal line
• Mitochondrial genes are more prone for mutation

Question 14

Centromere divides the chromosome into two arms… what are they?

Answer 14

p arm (short
q arm (long)

Question 15

What are the hierarchical levels of chromatin packaging in a human chromosome?

Answer 15

DNA double helix (2nM) < nucleosome fiber “beads on a string” (10nM) <Solenoid (30nM)

Question 16

Condensation begins during what phase of Mitosis?

Answer 16

Prophase

Question 17

During what phase of Mitosis is a chromatid maximally condensed and fully visible?

Answer 17

Metaphase

Question 18

The microtubules attach to the _____ during cell division

Answer 18

centromere kinetochores

Question 19

Genes are present in the telomeres and the centromere

Answer 19

FALSE!!!

Genes are usually absent in the telomeres and the centromere

Question 20

Chromosome nomenclature denotes 3 types of chromosomes. What are they?

Answer 20

• Metacentric chromosome
• Submetacentric chromosome
• Acrocentric chromosome

Question 21

Describe and give examples of metacentric chromosomes.

Answer 21

• p and q arms are of equal length.

- Centromere in the centre: Chromosome 1

Question 22

Describe and give examples of submetacentric chromosomes.

Answer 22

p arm is shorter than q arm: Chromosome 4

Question 23

Describe and give examples of Acrocentric chromosomes.

Answer 23

• p arm contains little genetic information.

- Chromosome 13, 14, 15, 21, 22: Involved in Robertsonian translocation

Question 24

Describe a standard Karotype.

Answer 24

22 pairs of autosomes and one pair of sex chromosomes (Total: 23 pairs of chromosomes)