2.2: Chromosomes

Question 1

Prokaryotic chromosome

Answer 1

1. One single chromosome called the genophore
2. located in nucleoid region ( no membrane bound nucleus)
3. DNA is circular and naked (no histones)
4. DNA is more compact (no introns)

Question 2

Plasmid

Answer 2

1. genetic structure in a cell that can autonomously replicate and function independently of the chromosome
2. typically a small, circular DNA strand in the cytoplasm of a prokaryote

Question 3

Plasmid function

Answer 3

1. may contain one or several genes related to a specific function i.e digestion of a specific food source or antibiotic resistance
2. can be exchanged between bacteria (sometimes inter-species)
3. provide the mechanism for traits including antibiotic resistance to spread, creating a competitive advantage
4. easy to manipulate and very stable = numerous lab applications

Question 4

Bacterial conjugation

Answer 4

• mechanism through which plasmids are exchanged

- occurs via the sex pilli

Question 5

Chromosomes during interphase

Answer 5

only visible with an electron microscope in less organised form called chromatin

Question 6

During first stages of division

Answer 6

chromosomes condense to form highly organised x shaped structures visible with a light microscope

Question 7

Sister chromatids

Answer 7

two identical lines of DNA making up the X shape and joined at the Centromere

Question 8

Chromosomes in anaphase

Answer 8

sister chromatids separate, each chromatid is now considered a chromosome

Question 9

Homologous chromosomes

Answer 9

two versions of the same chromosome, carrying the same set of genes in the same location but with varied alleles

Question 10

autosomes

Answer 10

chromosomes that do not influence sex determination (22 pairs)

Question 11

T2 Phage base pairs

Answer 11

0.18 million

Question 12

E-Coli base pairs

Answer 12

5 million base pairs

Question 13

fruit fly (drosophila melanogaster) base pairs

Answer 13

140 million base pairs

Question 14

homo sapien

Answer 14

3,200 million base pairs

Question 15

Parrs japonica (woodland plant) base pairs

Answer 15

150,000 million

Question 16

genome size and number of genes

Answer 16

• genome size does not always correlate with number of genes as some parts of a chromosome do not code for polypeptides
• general correlation but numerous outliers

Question 17

Diploid

Answer 17

nucleus contains two copies of each chromosome

Question 18

haploid

Answer 18

nucleus contains one chromosome from each pair, found in gametes and formed by diploid meiosis

Question 19

which gamete determines sex

Answer 19

fathers gamete as it contains 22 autosomes and either an x or a y sex chromosome that joins with the ovum to make either xx or xy

Question 20

zygote

Answer 20

single, diploid cell formed by the merging of sperm and egg

Question 21

homologue

Answer 21

each chromosome in a homologous pair

Question 22

tetrad

Answer 22

structure consisting of 4 chromatids, 2 x shaped chromosomes

Question 23

chromosome number

Answer 23

number of chromosomes is a characteristic feature of a species

Question 24

equine round worm chromosome number

Answer 24

4

Question 25

oryza sativa (rice) chromosome number

Answer 25

24

Question 26

Pan troglodytes (chimpanzee) chromosome number

Answer 26

48

Question 27

human chromosome number

Answer 27

46

Question 28

canis familiaris chromosome number

Answer 28

78

Question 29

best mitptic phase for viewing

Answer 29

metaphase: chromosomes are fully condensed and viewable

Question 30

karyogram

Answer 30

image showing homologous chromosomes aligned by descending length

Question 31

Karyotype

Answer 31

property of a cell: number and type of chromosomes present in a nucleus

Question 32

Use of Karyogram

Answer 32

deduce sex, find missing or extra chromosomes and detect chromosomal mutations, CANNOT detect mutations of single genes

Question 33

Autoradiography

Answer 33

technique made by John Cairns to measure the length of DNA molecules. Uses X ray film to visualize the two dimensional distribution of a radioactively labeled substance

Question 34

Autoradiography technique

Answer 34

• produced thymidine labelled with radioactive hydrogen
• grew e-coli in the radioactive thymidine medium allowing the DNA to replicate and become radioactive
• lyse the cells and release contents onto slides
• cover slides with photographic emulsion and store in the dark for two months
• high energy electrons emitted by the radioactive decay cause dark spots to appear
• pattern of dark spots indicated presence of lablled DNA