3.2 chromosomes

Question 1

how is DNA stored in prokaryotes

Answer 1

Prokaryotes do not possess a nucleus – instead genetic material is found free in the cytoplasm in a region called the nucleoid

The genetic material of a prokaryote consists of a single chromosome consisting of a circular DNA molecule (genophore)

The DNA of prokaryotic cells is naked – meaning it is not associated with proteins for additional packaging

In addition to the genophore, prokaryotic cells may possess additional circular DNA molecules called plasmids

Question 2

plasmids(def, present in?)

Answer 2

Plasmids are small, circular DNA molecules that contain only a few genes and are capable of self-replication

Plasmids are present in some prokaryotic cells, but are not naturally present in eukaryotic cells

Question 3

bacterial conjugation

Answer 3

Bacterial cells may exchange plasmids via their sex pili, in a process known as bacterial conjugation

This exchange of genetic material allows bacteria to evolve **new features within a generation **(horizontal gene transfer)

Question 4

what makes plasmids ideal vectors for gene manipulation in labs

Answer 4

ability to self-replicate and autonomously synthesise proteins,

Question 5

how is genetic material stored in eukaryotic cells

Answer 5

The genetic material of eukaryotic cells consist of multiple linear molecules of DNA that are associated with histone proteins

The packaging of DNA with histone proteins results in a greatly compacted structure, allowing for more efficient storage

Question 6

chromosome stain (e.g. and purpose)

Answer 6

Staining chromosomes with particular dyes (e.g. Giemsa stain) will additionally generate unique banding patterns - this will aid in recognising the chromosomes

Question 7

three references for region of locus

Answer 7

1. first number demotes chromosome
2. then p/q to denote p arm or q arm (p short, q long)
3. then number to correspond to band location - longitudinal

e.g. 7q31 - 7th chromosome, q arm, 3st longitudinal position.

Question 8

homologous chromosomes

Answer 8

are chromosomes that share:

1. The same structural features (e.g. same size, same banding patterns, same centromere positions)
2. The same genes at the same loci positions (while the genes are the same, alleles may be different)

Question 9

diploid

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Answer 9

• nuclei that possesses two gene copies (alleles) for each trait
• all somatic cells are diploid, with new diploid cells created via mitosis.
• diploid cells are present in most animals and many plants

Question 10

haploid

Answer 10

Nuclei possessing only one set of chromosomes are haploid (symbolised by n)

• These nuclei will possess a single gene copy (allele) for each trait
• All sex cells (gametes) in the organism will be haploid, and are derived from diploid cells via meiosis
• Haploid cells are also present in bacteria (asexual) and fungi (except when reproducing)

Question 11

sex chromosomes

Answer 11

pair of sex determining chromosomes,
XY male
XX female

Question 12

autosomes

Answer 12

all chromosomes except sex chromosomes

Question 13

karyogram

Answer 13

number and types of chromosomes in a eukaryotic cells.

Question 14

how are karyotypes determined

Answer 14

1. harvesting cells (usually from a fetus or white blood cells of adults)
2. chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
3. the stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not

Question 15

use of karyotyping prenatally

Answer 15

1. determine the gender of the unborn child
2. test for chromosomal abnormalities (aneuploidies or translocation - when a chromosome breaks and the fragmented pieces re-attach to different chromosomes.

Question 16

down syndrome

Answer 16

a condition whereby the individual has 3 copies of chromosome 21.
caused by a non-disjunction event in one of the parental gametes.
extra genetic material causes mental and physical delays in the way the child develops

Question 17

autoradiography - process to measure length of DNA molecules

Answer 17

1. Cells are grown in a solution containing radioactive thymidine (tritiated thymidine – 3H-T)
2. The tritiated thymidine is incorporated into the chromosomal DNA of the cell (3H-T is used as thymidine is not present in RNA)
3. The chromosomes are isolated by gently lysing the cells and fixing the chromosomes to a photographic surface
4. The surface is then immersed in a radioactively-sensitive emulsion containing silver bromide (AgBr)
5. The radiation released from the tritiated thymidine converts the Ag+ ions in silver bromide into insoluble metal grains
6. Following a period of exposure, excess silver bromide is washed away, leaving the silver grains to appear as small black dots
7. When the photographic film is developed, the chromosomal DNA can be visualised with an electron microscope

Question 18

i’m tired