Flashcards in Session 3-Mitosis And Meiosis Deck (55):
What is a telomere?
Repeated sequence (TTAGGG) in humans at each end of chromosome/chromatid. Telomere becomes shorter every time cell divides
What is a chromatid?
One of two threadlike strands formed by division during mitosis and meiosis
What is a centromere?
Links sister chromatids and consists of repetitive sequences
What is the difference between sister and non-sister chromatids?
They both have the same genes but may have different alleles
What is the cell division for somatic cells called?
What does mitosis produce?
Two identical daughter cells with same chromosome content as parent cell
What happens in the G0 stage of the cell cycle?
Cells can leave the cell cycle and enter the inactive state of G0
What is the synthesis (S) phase of the cell cycle?
The interval when DNA replication takes place (chromosomes are duplicated)
What is the G1 phase of the cell cycle?
Interval of cell growth before DNA replication (chromosomes unduplicated)
Which phases are included in interphase?
G1, S and G2
What happens in the G2 phase of the cell cycle?
Interval following DNA replication when the cell prepares to divide
What are the 5 stages of mitosis?
What happens in prophase?
Nuclear membrane disappears
Chromosomes become visible
Spindle fibres appear
What happens in prometaphase?
Microtubule spindles attach to centromere
What happens in metaphase?
Chromosomes line up in middle (metaphase plate)
Random alignment of chromosomes
What happens in anaphase?
Microtubule spindles pull each replicated chromosome apart and chromatids separate and go to separate poles of cell
What is the name given when the chromatids are separated in anaphase?
Chromosome (46 chromosomes left in each cell)
What happens in telophase?
Nuclear membrane reappears
Cleavage forms (where the cell is cleaved)
What does meiosis produce?
Four non-identical haploid cells (produces eggs and sperm)
What happens in meiosis I?
Homologous pairs of chromosomes line up and separate
What are the stages of meiosis I?
What happens in prophase I?
Chromosomes are replicated
Nuclear membrane disappears
Homologous chromosomes "find" each other because near/identical sequence
What happens in metaphase I?
Homologous pairs line up in metaphase plane
What happens in anaphase I?
Homologous chromosomes separate
What happens in telophase I?
Nuclear membrane reforms
What is a homologous chromosome?
Pair of chromosomes of similar size and shape and same identical gene loci. One from mother, one from father.
What is a bivalent?
Homologous chromosomes attached to each other by chiasmata during first division of meiosis
What happens in meiosis II?
Chromosomes line up and chromatids separate
What are the stages of meiosis II?
What happens in prophase II?
Microtubules move one member of centriole pair to opp spindle pole in each of two daughter cells
Microtubules attach to chromosomes
Chromosomes recoil and shorten
What happens in metaphase II?
Microtubules, motor proteins and duplicated chromosomes interact, positioning all of the duplicated chromosomes midway between two spindle pairs
Unpaired chromosomes align at equator of cell
What happens in anaphase II?
Attachment between sister chromatids (centromere) of each chromosome breaks and two are moved to opp spindle poles
Each former sister is now a chromosome on its own
What happens in telophase II?
After cytoplasmic division, each daughter cell is haploid
All chromosomes are in an unduplicated state
Chromosomes uncoil and nuclear envelope reforms
What are the consequences of meiosis?
Maintains constant chromosome number from generation to generation
Generation of genetic diversity by random assortment of chromosomes and crossing over
How long does spermatogenesis take?
When and where does spermatogenesis start?
In the testes as soon as puberty starts
Why do spermatogonia go through mitosis as well as meiosis?
If only meiosis took place, you would run out of germ cells
Cell produced at an early stage in the formation of the spermatozoa. Spermatogonia first appear in the testes of the foetus but do not multiply significantly until after puberty
Cell produced in intermediate stage in the formation of the spermatozoa. Develop from spermatogonia
What happens in meiosis I in spermatogenesis?
Primary spermatocyte (diploid) becomes secondary spermatocyte (haploid)
What happens in meiosis II of spermatogenesis?
Sister chromatids separate and end up with four unique daughter cells which are called spermatids. These eventually mature (lose cytoplasm, get head and tail etc) in testes and eventually become sperm
How long does oogenesis take?
Why does mitosis take place in oogenesis?
To make more oogonium or to make a primary oocyte
When does oogenesis begin and when does it stop temporarily?
Begins in the foetal stage and stops in prophase I of meiosis during foetal development
How often does a primary oocyte go through meiosis and become an ovum?
Once a month
What is the goal of oogenesis?
Produce one big "egg" with all the cytoplasm, nutrients etc
What happens to the secondary oocyte if it is not fertilised?
It is shed during menstruation
What happens to the secondary oocyte if it is fertilised?
Meiosis II will be completed and it becomes a zygote
What are the consequences of missegregation in meiosis?
Third of all identified miscarriages
Leading cause of mental retardation
What is nondisjunction?
The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, resulting in abnormal distribution of chromosomes in daughter nuclei
What is aneuploidy?
Error in cell division resulting in daughter cells having an incorrect number of chromosomes
Why does aneuploidy of the sex chromosomes have fewer adverse effects than aneuploidy of autosomes?
Everyone has at least one X chromosome so an incorrect number of sex chromosomes will not have as adverse an effect as having an incorrect number of autosomes as this would be lethal. Extra sex chromosomes would simply condense into one/inactivate.
What is a karyotype?
Number and visual appearance of chromosomes in a cell nuclei of an organism or species
What is mitotic nondisjunction?
The failure in mitosis for two members of a chromosome pair to separate normally so both the chromosomes go to one daughter cell while none go to the other daughter cell.