3.2 Chromosomes

Question 1

Define autosomes

Answer 1

AUTOSOMES: chromosomes which do not determine the sex of the organsim

Question 2

Genetic material in prokaryotes

Answer 2

• no nucleus
• circular DNA - nucleoid (genophore)
• no proteins - naked DNA
• may have plasmids - additional circular small DNA (addition to genophore)

Question 3

Explain bacterial conjugation

Answer 3

Bacteria can transfer plasmids in bacterial conjugation

• sex pili help attach - exchange plasmids
• plasmids can self-replicate and produce rpoteins
• plasmids used as vectors in labs for genetic engineering

Question 4

Organisation of DNA in eukaryotic chromosomes

Answer 4

• DNA is packed by histones into octamers to form nucleosome
• nucleosomes linked with additional histone H1 protein- chromatosomes
• chromatosomes coil to form solenoid structure
• forms loops condened into chromosomes
• chromatin supercoils during division to form chromosomes

Question 5

Chromosome anatomy

Answer 5

Question 6

How locus position is identified

Answer 6

Locus 7q31

1. First number - chromosome in haryotype
2. Second - letter p/q determines on which arm (p - shorter, q - longer)
3. Third - number identifies G band (Giemsa banding - coloured chromosome sections produced)

Question 7

Define homologous chromosomes

Answer 7

HOMOLOGOUS CHROMOSOMES: maternal and paternal chromosomes of sexually repsoducing organisms with the same strcutural features and same genes at same loci positions (the genes themselves may be different)

Homologous chromosomes separated in meiosis to form haploid gametes

Question 8

Diploid vs haploid cells

Answer 8

Diploid (2n)

• pairs of homologous chromosomes (each from a parent)
• two gene copies for one trait
• somatic cells - created via mitosis

Haploid (n)

• one homologous chromosome
• gametes halpoid derived from diploid cells in meiosis
• also present in bacteria, fungi (don’t reproduce sexually)

Question 9

Define sex chromosomes (heterosomes)

Answer 9

SEX CHROMOSOMES: chromosomes which determine the sex of an organism (X and Y)

Y chromosome - male determining - SRY gene especially

Females homologous (XX), males - not homologous (XY)

Father is responsible for determination of sex

Question 10

Define karyotype

Answer 10

KARYOTYPE: number and types of chromosomes in a eukaryotic cell

Question 11

How karyotyping is done

Answer 11

1. Harvesting cells
2. Chemically initiating division - arresting mitosis while chromosomes are condensed
3. Chromosomes are stained - photographed -> karyogram
4. Chromosomes arranged in homologous pairs

Question 12

For what karyotyping can be used

Answer 12

1. Prenatal - genetic disease, sex determining

Down syndrome - genetic condition - 3 homologous pairs of 21st chromosome - trisomy 21 - caused by non-disjunction in one of parents’ gametes - causes mental and physical delays in development

Question 13

For what is autoradiography used

Answer 13

AUTORADIOGRAPHY:

1. Cells grown in radioactive thymidine solution
2. Radioactive thymidine incorporated into DNA
3. Chromosomes are isolated and fixed to a surface
4. Surface immersed in radioactive solution with AgBr
5. Excess wahsed away silver stains
6. Exposed on photographic film - chromosomes analysed

Question 14

Measuring chromosome length

Answer 14

Using autoradiography - using tritiated uracil

Question 15

Why are the genomes of plants the largest?

Answer 15

PLant genomes can vary drastically because due to the capacity for plant species to self-fertilise and become polyploid

Question 16

Types of chromosomes

Answer 16