Cells Cycles And Divisons Flashcards
What are the 4 main events in the cell cycle in all organisms?
Cell division signals
DNA replication
DNA segregation
Cytokinesis
What is cell division in prokaryotes called?
Binary fission
What happens in binary fission?
Cell division signals- usually external factors such as nutrient concentration and environmental conditions
Replication- most prokaryotes have one circular chromosome, with two important regions. ori- where replication starts and ter- where replication ends
DNA segregation- when replication completed, ori regions move to opposite ends of the cell, segregating the daughter chromosomes
Cytokinesis- cell membrane pinches in, protein fibers form a ring. New cell wall materials are synthesized, resulting in separation of two cells
What happens in interphase of the cell cycle in eukaryotes?
Nucleus visible
Cell function occurs
3 subphases:
G1- Chromosomes are unreplicated
Duration variable
Ends at G1 to S transition when commitment is made to DNA
replication
S- DNA replicates
Sister chromatids remain together until mitosis
G2- Cell prepares for mitosis
What are the stages of mitosis?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
What does mitosis produce?
Two identical daughter cells, diploid
What is prophase in mitosis?
Chromosomes visible but condensing
Chromosomes match up with their homologous pairs
What is metaphase in mitosis?
Chromosomes line up in the middle of the cell in their pairs
What is anaphase in mitosis?
Spindle fibres pull sister chromatids to opposite sides of the cell
What is telophase in mitosis?
New nuclei form around the chromatids
What is cytokinesis in the cell cycle?
Splitting of the cytoplasm to create two new cells
What does meiosis produce?
4 genetically non identical cells, called gametes. Haploid
How does meiosis differ from mitosis?
Meiosis goes through two lots of prophase, metaphase, anaphase, telophase and cytokinesis, whereas mitosis goes through one lot. However despite going though two rounds, DNA is only replicated once
On the 2nd round of meiosis, chromosomes are not in pairs
How does meiosis generate genetic diversity?
Through recombination, crossing over and independent assortment of alleles
What are the errors in meiosis?
Inherited disorders can arise due to abnormal meiosis:
Abnormalities in chromosome number
Chromosome structural arrangement
Can be visualised and detected on a karyotype
How can meiosis cause abnormal chromosome numbers?
Due to nondisjunction, when pairs of homologous chromosomes or sister chromatids fail to separate
Different outcomes if this occurs in meiosis I or meiosis II
Meiosis I: two gametes that lack that chromosome and two gametes with two copies of the chromosome
Meiosis II: one gamete lacks that chromosome, two normal gametes, and one gamete with two copies of the chromosome
What is euploid?
Having the appropriate number of chromosomes
What is aneuploid?
Having an inappropriate number of chromosomes
What is monosomy?
Having loss of 1 chromosome
What is trisomy?
Having an extra chromosome
How can meiosis causing chromosome structural arrangement be bad?
Can be partial duplications, deletions, inversions and translocations that occur during crossing over
Can lead to disease
What is the advantages of 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 haploid?
More efficient cell cycle/faster division
More rapid growth
Survival in resource poor conditions
