3.2 Chromosomes Flashcards
Where can genetic material be found in prokaryotes?
As prokaryotes have no nucleus, genetic material found free in cytoplasm in nucleoid (single chromosome of naked circular DNA molecule, genophore). Prokaryotes can also have additional circular DNA (plasmids)
What is a plasmid?
Small, circular DNA molecules that contain a few genes and are capable of self-replicating. Can only be found in some prokaryotic naturally, not eukaryotic cells.
What is bacterial conjugation?
When bacterial cells exchange plasmids to evolve new features within a generation.
What are eukaryotic chromosomes?
Linear molecules of DNA that are associated with histone proteins.
ORGANISATION:
1. DNA put with 8 histone proteins to form nucleosome
2. Nucleosomes linked by additional H1 histone to form chromatosomes
3. Chromatosomes coil (~6 chromatosomes per turn) to form 30 nm fibre
4. Fibres form loops, which compress and fold around protein scaffold to form chromatin
5. Chromatin supercoils during cell division to form chromosomes
What are components associated with eukaryotic chromosome structure?
Eukaryotic chromosomes are compacted during cell division.
Each chromosome has centromere, which divides chromosome into two arms.
How can a specific locus be identified?
3 points of reference:
1. Number/letter which denotes chromosome (e.g. 7q31 = chromosome 7)
- p or q to indicate arm (e.g. 7q31 = q arm)
- Number corresponding to G band location (e.g. 7q31 = position 31
What are homologous chromosomes?
Chromosomes that share same structural features and same genes at same loci positions, but alleles can differ.
Homologous chromosomes must be separated in gametes (meiosis) before reproduction to prevent chromosome numbers doubling with each generation
What’s the difference between diploid and haploid nuclei?
Diploid nuclei possess pairs of homologous chromosomes (2n), meaning two gene copies for each trait. Thus, must be split in half for reproduction (gametes). Diploid cells are present in most animals and many plants.
Haploid nuclei possess only one set of chromosomes (n), meaning a single gene copy for each trait. All sex cells will be haploid, and is derived from diploid cells via meiosis. Haploid cells are also present in bacteria and fungi.
What does a chromosome number show?
Chromosome number is a characteristic feature for the members of a species. Usually, organisms with different diploid numbers cannot interbreed. In cases where different species can interbreed, offspring are usually infertile.
What is a karyogram?
A visual profile that shows the number and types of chromosomes in a eukaryotic cell. Chromosomes are arranged into homologous pairs and stained when photographed.
How is human sex determined?
Sex chromosomes (or heterosomes), X and Y.
Females have XX, males have XY.
Y chromosome contains genes for male sex characteristics, thus the absence of it develops female sex organs.
What is autoradiography?
When chromosomes are grown and isolated in order to develop a photographic film, which allows chromosomal DNA to be visualised with an electron microscope.
