L16: The Genome and its Transmission

Question 1

What is included in the total human genome?

Answer 1

All the nuclear DNA
AND
mitchondrial DNA

Question 2

Approximately how many base pairs are in the human genome?

How many genes are there ?

Answer 2

3200 million

23000 genes

Question 3

Particular sequences of DNA can do one of 4 things

Answer 3

1. Allow proteins to bind to switch a gene on or off
2. Produce RNA
3. Influence the activity of other genes (sometimes across great distances)
4. Affect how DNA is folded and packaged

Question 4

What is the genome?
What is the transcriptome?
What is the proteome?
Are they stable or dynamic?

Answer 4

The DNA sequence - stable
Complete set of RNA transcripts produce by a cell - dynamic
Complete set of proteins produced by a cell - dynamic

Question 5

Can a gene code for more than one protein? If yes, how?

Answer 5

yes

differential splicing

Question 6

22,000 genes known to encode untranslated RNA. What do these do?

• tRNA and rRNA
• snRNA and snoRNA
• microRNA
• tiny/longRNA

Answer 6

tRNA and rRNA are used in translation
snRNA and snoRNA modify other RNA molecules
microRNA - 22 nucleotides long, binds to mRNA inhibiting translation
tiny/long RNA have regulatory roles

Question 7

What is satellite DNA?

Answer 7

blocks of tandem repeats of nucleotides
can be mini - highly polymorphic
can be micro - small arrays of simple repeats

Question 8

What are the effects, purposes or uses of multiply repeated sequences?

• telomeres
• centromeres
• minisatellites
• small arrays of CAG repeats in noncoding regions
• small arrays of CAG repeats in coding regions

Answer 8

• allow replication of tip of chromosome, long repeats can be unstable so give rise to deletions of genes immediately below the telomere
• centromeres are essential for chromosome separation
• no known purpose, can cause mispairing
• no known purpose, vary from person to person, used in forensics
• no known purpose, can cause protein misfolding e.g. Parkinson’s disease

Question 9

Regulation of the genome (principally by regulating transcription) is paramount for… x3

Answer 9

growth
differentiation
cell specialisation

Question 10

What are chromosomes made of?

Answer 10

chromatin (DNA and proteins/packaged DNA)

Question 11

Which are the two main forms in which chromatin can exist? How to they stain?

Answer 11

Euchromatin - does not stain well, indicates an active cell

Heterochromatin - darkly staining, can exist in active or inactive forms, always inactive at centromeres

Question 12

Stages of mitosis

Answer 12

Interphase - growth, DNA replication
Prophase - chromosomes condense, spindles form at centrosomes
Prometaphase - nuclear envelope degraded, spindles attach to kinetochore
Metaphase - chromosomes line up
Anaphase - chromosomes separate, kinetochores shorten
Telophase - nuclear envelopes develop
Cytokinesis - cytoplasm divides

Question 13

Which directions do kinetochores face in prometaphase and metaphase?

Answer 13

Prometaphase - kinetochores face in opposite directions

Metaphase - kinetochores face in opposite directions

Question 14

What checkpoints are there in mitosis?

Answer 14

G1 checkpoint - Is the cell big enough to divide?
G2 checkpoint - Is all the DNA replicated? Is all the DNA damaged repaired?
Mitosis checkpoint - Are all chromosomes properly attached to spindle?

Question 15

What is the function of meiosis?

Answer 15

reduction division
reassortment of genes
genetic variation through crossing over, independent segregation

Question 16

Describe the mechanism of meiosis

Answer 16

Each homologue replicates to give two chromatids
Homologues pair
Exchange of material between non-sister chromatids (crossing-over)

Question 17

What are chiasmata?

Answer 17

The physical manifestations of crossing over

They hold paternal and maternal homologues together, stabilising them on metaphase plate

Question 18

What is the clinical importance of crossing over? How can it result in an incorrect prediction about someones genetic status?

Answer 18

DNA markers close to a gene can be used to identify and track alleles through a family
If a cross-over occurs between the marker and the altered allele, an incorrect predication about someone’s genetic status can result

Question 19

There may be several ……………. between non-sister chromatids, per ……………….

Answer 19

chiasmata

bivalent

Question 20

Describe gametogenesis in females

Answer 20

Oogeneisis ceases by the time of birth
At birth, primary oocytes are in maturation arrest, remaining suspended at the crossing-over stage. After puberty usually one oocyte a month completes meiosis.
Meiosis 1 is completed at ovulation when a single secondary oocyte is formed (which receives most of the cytoplasm) and the 1st polar body
Meiosis 2 is completed at fertilisation, forming a second polar body

Question 21

Describe spermatogenesis

Answer 21

Sperm are produced from spermatogonia
Each spermatogonium at the age of puberty is the result of about 30 successive cell divines
Each spermatogonium, then continues to divide every 16 days - one daughter cell remaining as a spermatogonium to continue division, the other daughter cell makes 4 spermatozoa