Mitosis and Meiosis Flashcards
What is mitosis
Part of the cell cycle that produces new cells with the same genetic content
Important processes involved in the production of identical daughter cells
DNA replication, chromosome duplication, chromosome separation
What is cell division
Process where a parent cell divides into 2 daughter cells
Where does mitosis occur
occurs in somatic cells (body cells) producing cells with a diploid number of chromosomes
Where does meiosis occur
occurs in the sex organs to produce sex cells (gametes) with a haploid number of chromosomes
What are the 2 mains phases in the mitosis cell cycle
Interphase (made up of 3 stages, 90% of cell cycle), M-phase consisting of mitosis (nuclear division) and cytokinesis (division of the cytoplasm at the end of telophase)
3 stages of interphase
First gap phase (G1)- cell increases in size and makes the mRNA and proteins needed for S phase, Synthesis (S)- cell duplicates its genetic material (chromosomes), Second gap phase (G2)- nucleus is well defined, rapid cell growth and protein synthesis, cell prepares for mitosis
Steps of cytokinesis
Interphase- DNA replicated, centrioles replicated, defined nucleus, Prophase- DNA condenses, nuclear membrane and nucleolus disintegrates, chromosomes appear as chromatids, miotic spindle forms, centrioles move to opposite poles, Metaphase- chromosomes line up on the equator of the cell, Anaphase- spindle fibres retract pulling chromosomes to opposite poles, cell elongates, Telophase- nuclei reform, cell elongates and furrow develops, Cytokinesis- 2 independent cells
What does meiosis produce
gametes for reproduction
What does meiosis involve
DNA replication, chromosome pairing, two successive nuclear divisions that distribute haploid sets of chromosomes to each gamete
What must occur before meiosis
mitosis occurs forming 2 identical chromatids held together at the centromere
What steps in meiosis produce genetically different gametes
crossing over (prophase)- allows DNA to break and swap creating new gene combinations, random assortment (metaphase)- chromosomes independently line up resulting in variation of alleles, non-disjunction (anaphase)- homologous chromosomes fail to separate meaning extra of less chromosomes
What is crossing over
When chromatids cross and some genetic material from one chromatid can swap to the other chromatid
What is random assortment
Homologous chromosomes line up randomly in metaphase 1 meaning that different allele combinations are possible
What is non-disjunction
Failure of homologous chromosomes to separate properly during anaphase 1, Failure of sister chromatids to separate properly during anaphase 3
What can non-disjunction cause
chromosomal abnormalities- when a zygote is formed by a gamete that has undergone a non-disjunction event resulting in offspring having extra or missing chromosomes in every cell of their body, conditions such as Patau’s syndrome (trisomy 13), Edwards syndrome (trisomy 18), Down syndrome (trisomy 21), Klinefelter syndrome (XXY)
What causes Klinefelter syndrome
Error (nondisjunction) results in either the mother’s egg or the father’s sperm having the extra X chromosome (equal chance of either happening), If the reproductive cell with the extra x chromosome contributes to the genetic makeup of a child, the child will have one or more extra X chromosomes in each of the body’s cells
Who does Klinefelter syndrome effect and how
affects males physical, behavioural and cognitive development and functioning, causes problems such as a small penis, small testes and infertility, Affects 1 in every 500-1,000 newborn males
Difference between main processes of mitosis and meiosis
Mitosis- 1 duplication, 1 nuclear division
Meiosis- 1 duplication, 2 nuclear divisions
Difference of what mitosis and meiosis produce
Mitosis- produces 2 diploid cells, new cells for growth and repair
Meiosis- produces 4 haploid cells, gametes for sexual reproduction
Difference in homologous chromosomes in mitosis and meiosis
Mitosis- homologous chromosomes don’t pair off
Meiosis- homologous chromosomes do pair off
Difference in the makeup of chromosomes in mitosis and meiosis
Mitosis- chromosomes don’t change genetic makeup
Meiosis- genetic makeup of chromosomes can be changed through crossing over
Difference in separation in mitosis and meiosis
Mitosis- chromatids separate so that each new cell gets a complete set of daughter chromosomes
Meiosis- first division- members of homologous pairs separate so the new cell gets a haploid set of chromosomes, second division- chromatids separate giving 4 haploid cells
First steps of meiosis
Prophase 1: Nuclear membrane disappears, Centrioles move to poles, Spindle fibres form, Homologous chromosomes line up and overlap at the chiasmata which allows for the crossing over of genetic material
Metaphase 1: Homologous chromosomes line up randomly on the equator
Anaphase 1: Homologous chromosomes separate and move towards opposite poles (segregation)
Telophase 1: Cytoplasm divides to form 2 cells with a diploid number of chromosomes, Cells aren’t identical (unlike mitosis)
Second steps of meiosis
Interphase 11: No replication of DNA, only time passes
Prophase 11: Spindle fibres forming, Each daughter cell has 1 chromosome from each pair
Metaphase 11: Chromosomes (2 sister chromatids) line up on the equator
Anaphase 11: Chromatids separate each moving to the opposite pole so non-disjunction can occur
Telophase 11: Nuclear membrane forms, 4 haploid daughter cells are produced, 4 sperm but 1 egg (3 polar bodies)- to be covered in spermatogenesis and oogenesis
