3.2 Chromosomes Flashcards
what do prokaryotes possess instead of a nucleus?
nucleoid (genetic material found free in the cytoplasm)
what does the genetic material of a prokaryote consist of? (2)
- single chromosome consisting of a circular DNA molecule (genophore)
- the DNA of prokaryotic cells is naked (not associated with proteins for additional packaging)
what do prokaryotic cells possess in addition to the genophere?
plasmids (circular DNA molecules)
what are plasmids?
- small circular DNA molecules that contain only a few genes and are capable of self-replication
what do bacterial cells do with plasmids?
- exchange plasmids via sex pili in a process called bacterial conjunction
what does the exchange of genetic material allow for bacteria?
allows bacteria to evolve new features within a generation (horizontal gene transfer)
why are plasmids ideal vectors for gene manipulation in labs? (2)
they can self-replicate and autonomously synthesise proteins
what does the genetic material of eukaryotic cells consist of? (2)
- multiple linear molecules of DNA that are associated with histone proteins
- the packaging of DNA with histone proteins result in a compact structure for ore efficient storage
what is the organisation of eukaryotic chromosomes? (5)
- DNA is complexed with 8 histone proteins (octamer) to form a nucleosome
- nucleosomes are linked by an additional histone protein (H1 histone)
- these coil to form a solenoid structure which is condensed to form a 30nm fibre
- these fibres then form loops which are compressed and folded around a protein scaffold to form chromatin
- chromatin will supercoil during cell division to form chromosomes that re visible (stained) under microscope
what is the constriction point of a chromosome called?
centromere
why is it significant that sexually reproducing organisms inherit their genetic sequences from both parents?
these organism will possess 2 copies of each chromosome
what are maternal and paternal chromosome pairs called?
homologous chromosomes
what do homologous chromosomes share?
- the same structural features (eg. same size, banding patterns, centromere positions)
- same genes at the same loci positions
why must homologous chromosomes be separated in gametes (via meiosis)?
to prevent chromosome numbers continually doubling with each generation
why do sexually reproducing organisms have 2 sets of chromosomes (diploid)?
receive genetic material from both parents
what must organisms must do to create gametes from the diploid chromosomes?
- they must create gamete with half the number of chromosomes (haploid)
what occurs when 2 haploid gametes fuse?
it results in a diploid cell (zygote) which grows into new organism
what are the characteristics of diploid cells? (4)
- possess pairs of homologous chromosomes(in nuclei)
- nuclei will possess 2 gene copies (allele) for each trait
- all somatic (body) cell in the organism will be diploid with new diploid cells created via mitosis
- diploid cells are present in most animals and many plants
what are the characteristics of haploid cells? (4)
- nuclei possessing only 1 set of chromosomes are haploid
- these nuclei will possess a single gene copy(allele) for each trait
- all sex cells (gametes) in the organism will be haploid and are derived from diploid cells via meoisis
- haploid cells are also present in bacteria (asexual) and funji (except when reproducing)
how is sex determined in humans?
sex chromosomes (pairs of chromosomes)
what sex chromosomes do females possess?
2 copies of X chromosome (XX)
what sex chromosomes do males possess?
1 copy of X and 1 copy of Y (shorter)
what will the absence of a Y chromosome lead to?
female sex organs developing
which parent is always responsible for determining the sex of offspring?
- father
- is male sperm contain X chromosome then girl
- if sperm contain Y chromosome then boy
