Genetics: Meiosis Flashcards
Define meiosis
Explain the process of meiosis 1
• P-I:Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
• M-I:Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
• A-I:Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
• T-I:Chromosomes decondense, nuclear membranemayreform, cell divides (cytokinesis) to form two haploid daughter cells
Explain the process of meiosis 2
• P-II:Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
• M-II:Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
• A-II:Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
• T-II:Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
The advantage of meiotic division?
The advantage of meiotic division and sexual reproduction is that it promotes genetic variation in offspring.
Meiosis is responsible for the production of gametes
The three main sources of genetic variation arising from sexual reproduction are:
Crossing over
Random Orientation
Random Fertilisation
Explain how crossing over leads to genetic variation
• The exchange of genetic material occurs betweennon-sister chromatidsat points calledchiasmata
As a consequence of this recombination, all four chromatids that comprise the bivalent will be genetically different
• Chromatids that consist of a combination of DNA derived from both homologous chromosomes are calledrecombinants
• Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
Explain how random orientation leads to genetic variation
When homologous chromosomes line up in metaphase I, their orientation towards the opposing poles israndom
The orientation of each bivalent occursindependently, meaning different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in anaphase I
Explain how random fertilisation leads to genetic variation
The fusion of two haploid gametes results in the formation of a diploid zygote
• This zygote can then divide by mitosis and differentiate to form a developing embryo
As meiosis results in genetically distinct gametes, random fertilisation by egg and sperm will always generate different zygotes
Identical twins are formedafterfertilisation, by the complete fission of the zygote into two separate cell
Differences in meiosis and mitosis
• Division– Mitosis involves only one cell division, but meiosis requires two cell divisions
• Independent assortment– Homologous pairs are randomly separated into separate cells in meiosis, but not mitosis
• Synapsis– Homologous pairs form bivalents in meiosis, but not mitosis
• Crossing over– Non-sister chromatids of homologous pairs may exchange genetic material in meiosis, but not mitosis
• Outcome– Mitosis results in the formation of two daughter cells, while meiosis produces four daughter cells
• Ploidy– Daughter cells produced by mitosis are diploid, while daughter cells produced by meiosis are haploid
• Use– Mitosis is used to clone body cells, while meiosis is used to generate sex cells (gametes)
• Genetics– Cells produced by mitosis are genetically identical (clones), while cells produced by meiosis are genetically distinct
Mnemonic:Disco Pug
Similarities in meiosis and mitosis
They are both preceded by interphase (which includes DNA replication)
They both divide according to a common pathway (prophase→metaphase→anaphase→telophase)
They both split their cells via cytokinesis
Meiosis and mitosis are both processes of cell division, and they share several similarities:
Both meiosis and mitosis involve the replication of DNA before cell division.
In both meiosis and mitosis, the chromosomes condense and become visible under a microscope.
Both processes involve the formation of a mitotic spindle,
Both meiosis and mitosis result in cell division.
both meiosis and mitosis undergo cytokinesis, the division of the cytoplasm, to form two separate daughter cells.
Advantages of mitotic division?
Mitosis is essential for the growth and development of multicellular organisms.
Mitosis plays a crucial role in tissue repair and regeneration.
Mitosis ensures that the chromosome number is maintained in each cell generation.
Mitosis produces genetically identical daughter cells, which helps maintain the genetic identity of the organism.
Mitotic division is the basis of asexual reproduction in many organisms.
What is the significance of independent assortment during meiosis?
Independent assortment refers to the random arrangement and separation of homologous chromosomes during meiosis. It contributes to genetic diversity by producing unique combinations of alleles in the resulting gametes.
