Topic 3.2 Chromosomes

Question 1

Prokaryotes

Answer 1

Have a single circular molecule made of naked DNA

May have additional plasmids (autonomous DNA units)

Question 2

Eukaryotes

Answer 2

Multiple Linear DNA molecules packaged with histone.

Do not have plasmids (unless genetically modified)

Question 3

Diploid

Answer 3

Sexually reproducing organisms receive genetic material from both parents
→ Diploid= 2 sets of chromosomes (i.e body cells)

Question 4

Haploid

Answer 4

To reproduce, these organisms only pass on half their genetic material
→ Haploid - 1 set of chromosomes (i.e sex cells / gametes)
When haploid sex cells fuse, the diploid cell can grow into a new organism.

Question 5

Homologous Chromosomes

Answer 5

Homologous Chromosomes are paired chromosomes inherited from both parents (maternal and paternal) in sexually reproducing animals.

Homologous Chromosomes Have the same genes at identical Loci positions
→ However specific alleles for each gene may be different.

Question 6

Karyotyping

Answer 6

Chromosome number is a characteristic feature of members of species
→ Karyotypes identify the number of types of chromosomes in a cell.

Question 7

Karyotyping use

Answer 7

Karyotyping is preformed pre-natally to identify the sex of offspring or diagnose potential chromosome abnormalities (e.g. aneuploidies)

Question 8

Amniocentesis Procedure

Answer 8

Cells are cllected from the amniotic fluid of the pregnant mother.
Conducted at ~16 weeks with a slight risk of miscarriage (~0.5%)

Question 9

Chorionic Villi Sampling Test

Answer 9

Cells collected directly from the placental tissue

Conducted at 11~ weeks with a higher risk of miscarriage (~1%)

Question 10

Autoradiography

Answer 10

John Cairn pioneered a technique for measuring the length of DNA while uncoiled (via autoradiography)

Question 11

Autoradiography steps

Answer 11

1. Radioactive thymidine is incorporated into cell’s DNA
2. Chromosomes were fixed to photographic surface and treated with silver bromide (AgBr)
3. Radiation converts ions into insoluble grains that is visible via electron microscopy when a film is developed.

Question 12

Sex Determination

Answer 12

Humans Have 23 pairs of Chromosomes
→ Diploid number (2n) = 46 chromosomes

22 pairs are homologous autosomes
→ Each pair has identical genes and loci
→ Alleles may differ (one from each parent)

The 23rd pair are the sex chromosomes
→ Females have two X chromosomes (XX)
→ Males have X and Y chromosomes (XY)

The Y chromosomes is responsible for the development of male characteristics
→ Hence, the father always determines sex

Question 13

Karyogram basic

Answer 13

A karyogram shows the chromosomes of a length cell in homologous pairs of decreasing length.