Mitosis and Meiosis Flashcards
What are the 2 types of cell division?
Binary fission: occurs in bacteria, asexual (1 cell becomes 2)
Mitosis: carried out by somatic (body) cells, allows multicellular organisms to grow in size, repair damaged cells and replace worn out cells
Meiosis: occurs in germ cells, produces gametes used for sexual reproduction
Describe interphase (stage 1 of the cell cycle)
G1: growth stage 1, cell grows and develops
S (synthesis): DNA gets replicated
G2: growth stage 2, any structures or proteins needed for cell division are produced
Describe Mitosis
1 cell becomes 2
Prophase: Chromatin condenses to form chromasomes, nuclear membrane and nucleolus dissolve, centrioles move to opposite sides
Metaphase: Chromosomes line up at the equator, spindle fibres form from centrioles and attach to the centromeres of the chromosomes
Anaphase: spindle fibres pull one sister chromatid (identicle chromosomes) to each side
Telophase: spindle fibres dissolve and chromatids get surrounded by a nuclear membrane, nucleolus reappears
Cytokinesis: division of ctyoplasm, animal cells form a cleavge furrow and plant cells form a cell plate
Describe Meiosis I.
Prophase I: homologous chromosomes pair up to form tetrads (recombination occurs, chromosomes exchange DNA
Metaphase I: tetrads line up at the equator randomly such that each side will have some maternal and some paternal
Anaphase I: tetrads are pulled apart, each side receives a pair of chromosomes
Telophase I: nuclear membrane reappears, spindle fibres dissapear and the 1 cell becomes 2
Describe Meiosis 2
Everything happens in 2 cells from meiosis I
Prophase II: Chromatin coil up, nuclear membrane dissolves and spindle fibres form
Metaphase II: chromosomes line up at the equator, spindle fibres connect to the centromeres
Anaphase II: spindle fibres contract and the chromosomes are seperated into chromatids
Telophase II: nuclear membrane reforms, spindle fibres dissolve, chromosomes uncoil and 2 cells become 4
What is a diploid number?
2n where n is the number of chromosomes contributed by each gamete
46 in humans
What is a haploid number
n where n is the number of chromosomes contributed by each gamete
23 in humans
What is Crossing Over?
The process by which maternal and paternal chromosomes exchange DNA
What is non-disjunction?
Failure of chromosomes to separate causing one gamete to have an extra chromosome and one to have a missing chromosome
What are some disorders caused by non-disjunction
Down Syndrome: an extra copy of chromosome 21
Trisomy 18/Edwards syndrome: extra chromosome 18
Klinefelter syndrome: extra X chromosome
Turner syndrome: Missing an X chromosome
Explain the 4 ways in which chromosome structure can be affected.
Duplication: a part of the chromosome is repeated
Inversion: a part of the chromosome is reversed
Insertion: the addition of base pairs to a DNA molecule
Translocation: a segment of DNA breaks off one chromosome and attaches to another, non-homologous chromosome
