3.2 Flashcards
What does prokaryote genome consist of?
a single circular chromosome and plasmids
Describe the structure of a prokaryotic chromosome
one chromosome consisting of a circular DNA molecule
What are plasmids?
what kind of genes are found on plasmids?
what happens to plasmids when prokaryotes divide?
small loops of naked DNA free in cytoplasm
genes not needed for basic life processes but may provide survival advantages (eg. antibiotic resistance)
plasmids may not be replicated simultaneously as the chromosome, so may not be passed on to daughter cells
Explain Cairns technique for measuring the length of DNA
- E. coli cells were grown in a solution containing tritiated thymidine, in order to produce radioactively labelled DNA
-They were then placed onto a dialysis membrane & their cell walls wer digested by lysozyme to release their DNA into the surface
-A thin photographic emulsion was applied to the surface of the membrane & left in darkness for two months
-After this, the film was developed and analysed using an electron microscope
-At each point where tritium atoms decayed, there was a dark grain, indicating the position of DNA
-Cairns images showed that E. coli’s chromosome was a single circular DNA molecule
-They also showed replication forks, and the long linear structure of chromosomes
Describe the structure of eukaryotic chromosome
eukaryotic chromosomes are linear DNA molecules associated with histones (to form nucleosomes)
What are homologous chromosomes?
homologous chromosomes are pairs of chromosomes (1 from each parent) with the same length, centromeres in the same position, and same genes at the same loci (may have different alleles of those genes)
Compare the genome size of different organisms
mbp
T2 phage: virus that infects E. coli: 0.18
E. coli: gut bacterium: 5
Drosophila melanogaster: fruit fly: 140
Homo sapiens: humans: 3000
Paris japonica: woodland plant: 150000
What are diploid nuclei?
diploid nuclei have pairs of homologous chromosomes
have 2 copies of each gene, 2 complete sets of chromosomes, have 2 chromosomes of each type
What are haploid nuclei?
haploid nuclei have only one chromosome of each pair
have 1 copy of each gene, have 1 complete set of chromosomes, have 1 chromosome of each type
What is the number of chromosomes a characteristic of?
The number of chromosomes is a characteristic of members of a species, where organisms with different numbers of chromosomes are unlikely to be able to interbreed. Very rarely during evolution, can the number of chromosomes of a species change.
Number of chromosomes can increase if a chromosome splits into two
Number of chromosomes can decrease if two chromosomes fuse together
Comparison of diploid chromosome numbers
chromosome number has no valid indication of genetic complexity
Parascaris equorom: roundworm: 4
Oryza sativum: rice: 24
Homo sapiens: humans: 46
Pan troglodytes: chimpanzees: 48
Canis familiaris: dog: 78
What is sex determined by?
sex is determined by sex chromosomes
X chromosome:
- is relatively large
- has centromeres near the middle
- have many genes essential for both male and females
Y chromosome:
- much smaller than X chromosome
- centromeres near its end
- contains smaller number of genes
- only small part is homologous with X
What are autosomes ?
chromosomes that do not determine sex
What is a karyotype?
a karyotype is the number of chromosomes and type of chromosomes in its nuclei
What is a karyogram? and how is it done?
a karyogram is all of the chromosomes of an organism arranged in homologous pairs in order of decreasing length
it is made by taking cells during metaphase in mitosis
staining them to make them visible
bursting the cell to release the chromosome
taking a digital micrograph of the chromosomes for them to be digitally cut and arranged in order
