Topic 3.3: Meiosis Flashcards
Define meiosis
Meiosis is the process by which sex cells (gametes) are made in the reproductive organs
It involves the reduction division of a diploid germline cell into four genetically distinct haploid nuclei
Define sister chromatids
The two identical DNA molecules are identified as sister chromatids, and are held together by a single centromere
What happens during prophase I of meiosis I?
Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
What happens during metaphase I of meiosis I?
Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
What happens during anaphase I of meiosis I?
Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
What happens during telophase I of meiosis I?
Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
What happens during prophase II of meiosis II?
Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
What happens during metaphase II of meiosis II?
Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
What happens during anaphase II of meiosis II?
Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
What happens during telophase II of meiosis II?
Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
Defien synapsis
In prophase I, homologous chromosomes undergo a process called synapsis, whereby they pair up to form a bivalent (or tetrad)
Define chiasmata
The homologous chromosomes are held together at points called chiasmata (singular: chiasma)
What are The three main sources of genetic variation arising from sexual reproduction?
Crossing over (in prophase I) Random assortment of chromosomes (in metaphase I) Random fusion of gametes from different parents
Define non-disjunction
Non-disjunction refers to the chromosomes failing to separate correctly, resulting in gametes with one extra, or one missing, chromosome (aneuploidy)
Define karyotyping
Karyotyping is the process by which chromosomes are organised and visualised for inspection
What is chorionic villi sampling?
Chorionic villi sampling involves removing a sample of the chorionic villus (placental tissue) via a tube inserted through the cervix
What is aminocentesis?
Amniocentesis involves the extraction of a small amount of amniotic fluid (contains fetal cells) with a needle
What is the difference between mitosis and meiosis in terms of divisions?
Mitosis: one
Meiosis: two
What is the difference between mitosis and meiosis in terms of independent assortment?
Mitosis: no
Meiosis: yes (metaphase I)
What is the difference between mitosis and meiosis in terms of synapsis?
Mitosis: no
Meiosis: yes- form bivalents
What is the difference between mitosis and meiosis in terms of crossing?
Mitosis: no
Meiosis: yes (prophase I)
What is the difference between mitosis and meiosis in terms of outcome?
Mitosis: two cells
Meiosis: four cells
What is the difference between mitosis and meiosis in terms of ploidy?
Mitosis: diploid
Meiosis: haploid
What is the difference between mitosis and meiosis in terms of use?
Mitosis: body cells
Meiosis: sex cells (gametes)
What is the difference between mitosis and meiosis in terms of genetics?
Mitosis: identical cells
Meiosis: variation
Define polyploidy
Polyploidy is a condition whereby an organism has more than two complete sets of chromosomes in all cells
