Chromosomes

Question 1

Structure of (eukaryotic) chromosome

Answer 1

Linear Chromosome:
* Telomere
* Centromere
* Heterochromatin (gene-poor DNA)
* Euchromatin (“active” DNA)

Question 2

breifly describe telomeres

structure and function

Answer 2

• Repeats (of 5’-TTAGGG-3’)
• Hundreds of copies at the ends of chromosomes
• Some lost at mitosis - end replication problem
• Telomerase

Function: protect DNA ends (shorten as age)

Question 3

End-replication problem

Answer 3

The ends of linear DNA cannot be replicated completely during lagging strand DNA synthesis

Question 4

name the 5 phases of mitosis

Answer 4

• Prophase
• Metaphase
• Anaphase
• Telophase
  +Cytokenisis

PMAT

Question 5

Prophase

Answer 5

• chromosomes condense
• nuclear membrane disappears
• spindle fibres form from the centriole

Question 6

Metaphase

Answer 6

• chromosomes aligne at the equator of the cell
• attached by fibre to each centriole (by spindle fibres)
• Mex condensation of chromosome

Question 7

Anaphase

Answer 7

• sister chromatids seperate at centromere
• Seperate longitudinally
• Move to opposire ends of cell

Question 8

Telophase

Answer 8

• New nuclear membranes form
• Each cell contains 46 chromosomes (diploid)

Question 9

Cytokinesis

Answer 9

• cytoplasm seperates
• Two new daughter cells

Question 10

briefly explain centromeres

Answer 10

• Region joining sister chromatids
• Site of kinetochore attachement
• Required for chromosome seperation during cell division

Question 11

what is chromatin

Answer 11

a mixture of DNA and proteins that form the chromosomes

Question 12

what happens during interphase

weird question/answer ik - from PP

Answer 12

Genes are transcribes and DNA replication occurs (S phase)

Question 13

Heterochramatin

what is it and structure

Answer 13

Inactive DNA with “silenced” genes - condensed structure

Question 14

Euchromatin

what is it and structure

Answer 14

Active genes and open structure

Question 15

Proportion of DNA that is protein coding

Answer 15

Not much: ~2%

Question 16

what are extragenic sequences

Answer 16

DNA space between two genes of a genome

Question 17

What can extragenic sequences include

Answer 17

• Tandemly repeated DNA sequences
  satellite DNA
  Minisatellite DNA
• highly repeated interspersed DNA sequences - not sure what they are… no biological function

Question 18

functions of non-coding DNA

Answer 18

• regulation of gene expression
  as such, regulation of protein synthesis

Question 19

What is the structure of chromatin

Answer 19

DNA packed with histone proteins to form chromatin
Packaged into units called nucleosomes

Question 20

nucleosomes

Answer 20

segments of DNA wrapped around histone proteins - “beads on a string”

Question 21

how does DNA bind to histones

Answer 21

charge (DNA -ve and histone +ve)

Question 22

what does further wrapping of nucleosomes form

Answer 22

solenoid structure

Question 23

packaging of DNA order

Answer 23

DNA-histone-nucleosomes-solanoid scaffold loop chromatids-chromosome

Question 24

What is the purpose of packaging DNA

Answer 24

• -ve DNA neutralised by +ve histone proteins
• DNA takes up less space

Question 25

what can we do to inactive dna

Answer 25

fold it into inaccessible locations until required

Question 26

what is inactive chromatin characterised by | don't need to know?

Answer 26

specific histone covalent modification

Question 27

p arm

Answer 27

**shortest** arm on chromosome based on distance from centromere | Think: p = petite

Question 28

q arm

Answer 28

longer arm on chromosome based on distance from centromere

Question 29

karayotype

Answer 29

an individual's complete set of chromosomes

Question 30

number of chromosomes humans have

Answer 30

46 (23 pairs)

Question 31

fluorescent in situ hybridisation - FISH

Answer 31

fluorescent DNA probes to target specific chromosomal locations within the nucleus, resulting in colored signals that can be detected using a fluorescent microscope

Question 32

4 types of FISH probes and describe a bit about each/some of them | FISH = fluorescent in situ hybridisation

Answer 32

* Unique sequence probes * Centrometic probes - determine chromo **number** * Telomeric probes - detect subtelomeric rearrangements * Whole chromosome probes - spectral karyotype, detect translocations and rearrangements

Question 33

what is a germ cell

Answer 33

cells in the body that develop into sperm and eggs

Question 34

Summarise meosis (start and end points not whole process)

Answer 34

* Cell division in germ cells * Diploid cells (in ovaries and testes) divide to form **haploid** cells * Chromosomes are passed on as re-arranged (**recombined**) copies - creates genetic diversity

Question 35

what happens in chromosome numbers duuring meiosis and recombination

Answer 35

Diploid (2n) becomes two haploid (n) cells 46---> 2x23

Question 36

summarise meiosis and recombination

Answer 36

single round of DNA replication but 2 rounds of cell division: PMAT and then 2nd miotic division where attachment between sister chromatids is broken and they seperate

Question 37

gametogenesis

Answer 37

production of gametes from haploid precursor cells

Question 38

oogenesis

Answer 38

process of egg formation

Question 39

spermatogenesis

Answer 39

process of sperm formation

Question 40

difference between oogenesis and spermatogeneis in males and females | (both=gametogenesis)

Answer 40

* sperm go through **more** cells divisions - more chance on mutation * **Duration**: sperm 60-65 days, eggs 10-50 years * **Commences**: puberty in males and early embrionic life in females * **Gamete production per mitosis**: 4 spermatids and 1ovum + 3 polar bodies * **Gamete production**: 100-200 million per ejaculate compared to 1 ovum per menstrual cycle * **No. mitoses in gamete formation**: 30-500 in males and 20-30 in females | see sheet

Question 41

XX

Answer 41

female

Question 42

XY

Answer 42

male

Question 43

what determines gender of embryo

Answer 43

whether sperm contains X or Y chromosome

Question 44

Fertilisation

Answer 44

Two haploid cells (egg, sperm) form 1 diploid cell (**Zygote**)

Question 45

where does the embryo get its genetic material

Answer 45

assortment of genes from each original parent - inc genetic diversity

Question 46

Where can the mitochondria and its DNA only come from

Answer 46

**Mother** via the egg - maternal inheritance

Question 47

why does X-inactivation occur in females

Answer 47

females have a double does of gene product on X-chromosome

Question 48

what does X-inactivation in females occur

Answer 48

random inactivation of one X chromosome - can result in funny things if mutation on one chromo and not the other

Question 49

types of structural chromosome abnormalities

Answer 49

Four main types of structural chromosomal aberrations are **deletion, duplication, inversion, and translocation**