1. 3.2 - Chromosomes

2. Essential Idea: Chromosomes carry genes in a linear sequence that is shared by members of a species.
3.2
Chromosomes
Understandings:
Prokaryotes have one chromosome consisting of a circular DNA molecule
Some prokaryotes also have plasmids but eukaryotes do not
Eukaryote chromosomes are linear DNA molecules associated with histone proteins
In a eukaryote species there are different chromosomes that carry different genes
Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
Diploid nuclei have pairs of homologous chromosomes
Haploid nuclei have one chromosome of each pair
The number of chromosomes is a characteristic feature of members of a species
A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.
Applications:
Cairn’s technique for measuring the length of DNA molecules by autoradiography
Compare genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica
Compare diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum
Use karyograms to deduce sex and diagnose Down syndrome in humans
Skill:
Use of databases to identify the locus of a human gene and its polypeptide product

3. Prokaryote chromosomes
A. Single circle of DNA

4. Plasmids – small loops of extra DNA
1. Replicate independently
2. Usually not needed under normal conditions but useful in unusual circumstances

5. II. Eukaryote Chromosomes A
II. Eukaryote Chromosomes A. During interphase, DNA found as chromatin – DNA and histones

6. Homologous pairs – similar shape, size, carry same genes (One from mom, one from dad)
1. Alleles – different forms of the same gene

7. Prokaryotes
Eukaryotes
Number of Chromosomes 1
2 or more
Shape
Circular
Linear
Histones
Not present
Present
Plasmids present
Sometimes
Never
Organized in pairs No
Yes

8. III. Diploid and Haploid Cells A
III. Diploid and Haploid Cells A. Diploid (2n)– 2 complete sets of chromosomes – one from mom, one from dad 1. Most cells in your body (somatic cells) B. Haploid (n)– sex cells (gametes, egg, sperm) – 1 set of chromosomes Ex. Humans – n=23, 2n=46

9. C. Chromosome number is a defining feature of a species

10. Karyotypes – pair and displays chromosomes to identify and diagnose abnormalities
A. Place homologous pairs together in order of size and then sex chromosomes

11. Sex Determination
A. Sex chromosomes
1. Females – XX
2. Males XY
B. All other chromosomes called“autosomes”

12. Use film to capture radiation being given off by a substance
Autoradiography
Use film to capture radiation being given off by a substance
Can be used to measure the length of DNA strands
Cairns’ technique – inject radio markers (radioactive thymidine-contains 3H) into the DNA to expose film faster
Used it to show that a bacterial chromosome is circular, called them “theta structures