cell cycles and divisions Flashcards
what are the 4 main events in all organisms included in the cell cycle, although they occur differently in prokaryotes and eukaryotes
- cell division signals
- DNA replication
- DNA segregation
- cytokinesis
during what process do prokaryotes divide
binary fission
give 2 examples of external factors that are cell division signals in prokaryotes
- nutrient concentration
- environmental conditions
what is replicated in prokaryotes
circular chromosome
where does replication start and end (3 letter name)
ori - start
ter - end
in prokaryotes where do ori regions move to after replication is complete
ori regions move to opposite ends of the cell, segregating the daughter chromosomes
what happens in prokaryotes during cytokinesis
- cell membrane pinches in, protein fibres form a ring
- new cell wall materials are synthesised, resulting in separation of the two cells
what happens in eukaryotes during interphase
- nucleus is visible
- cell functions occur
- 3 growth subphases (G1, S and G2)
what happens at the G1 phase in eukaryotes
- chromosomes are single
- ends at G1-to-S phase when commitment is made to DNA replication and cell division (cannot be reversed)
what happens in the S phase in eukaryotes
- DNA replicates
- sister chromatids remain together until mitosis
what happens in the G2 phase in eukaryotes
- cell prepares for mitosis (e.g. synthesising the structures that move the chromatids)
what happens during mitosis in eukaryotes
- produces 2 genetically identical nuclei (barring errors in DNA replication / mutations)
what type of reproduction is based on mitosis
asexual reproduction
what type of reproduction requires meiosis
sexual reproduction
describe the process and results of meiosis
- 2 nuclear divisions, but DNA is replicated only once
- reduces chromosome number from diploid to haploid, with each haploid having a complete set of chromosomes
- gametes created
- offspring is not genetically identical to the parents
through which 2 processes is genetic diversity introduced via meiosis
recombination - crossing over
independent assortment of alleles
what 2 ways can inherited disorders arise due to abnormal meiosis
abnormalities in chromosome number
chromosome structural rearrangements ( crossing over is uneven)
what happens if nondisjunction occurs during meiosis I
2 gametes lack that chromosome and 2 gametes with 2 copies of the chromosome
what happens if nondisjunction occurs during meiosis II
one gamete lacks that chromosome, 2 normal gametes, and one gamete with 2 copies of the chromosome
what are the advantages of being diploid
- can repair DNA damage using other chromosome copy
- recessive mutations can be masked
- more rapid evolution possible
- greater diversity of immune gene alleles
what are the advantages of being haploid
- more efficient cell cycle allows faster division
- more rapid growth
- survival in resource poor conditions
what were the 2 successes in Mendel’s experiments
- true breeeding lines (binary, predictable traits)
- large sample size
how do bacteria exchange genes
by conjunction, via a sex pilus extending from one cell to another
genetic material passes through a cytoplasmic bridge called the conjugation tube
how do prokaryotic cells inherit DNA
- DNA passes from a donor cell to recipient cell
- donor and recipient DNA line up and crossing over can occur, changing the recipient’s genetic makeup
