Meiosis Flashcards
What does diploid mean
Cell that contains 2 copies of each chromosome
Somatic cells
Body tissues which undergo mitosis
Haploid
A cell which contains 1 copy of each chromosome
Gamete
A reproductive cell that is formed through meiosis (sperm, ovum)
Germ line cell
Reproductive cells responsible for gametogenosis (formation of gamete’s) in humans the 23 pairs of chromosomes are referred to as homologous
Homologous chromosome
Pairs of chromosomes that have the same length, centromere location, genes, and banding pattern when stained with specific dyes
Not identical to each other, but contain genes that code for same trait
Meiosis
Process by which sex cells or gametes are formed, occurs in testes and ovaries in humans
Involves 2 nuclear divisions
Results in the 4 daughter cells having half the number of chromosomes as the original parent cell (haploid)
Meiosis I?
Called reduction division because the diploid chromosome number is reduced to haploid
What is happening in prophase I?
Nuclear envelope begins to dissolve, centrioles move to opposite poles and spindle fibres form
Homologous chromosomes are held tightly along their lengths referred to as synapsis (foursome of chromatids)
Crossing over happens
What is crossing over?
Process whereby the chromosomes synapse, chromosomes intertwine and break and exchange segments
Permits exchange if genetic info = genetic variation
Metaphase I (meiosis)
Homologous chromosomes attach to spindle fibres and line up at equatorial plate
Anaphase I (meiosis)
Homologous chromosomes move towards opposite poles = segregation
One member of each homologous pair will be found in each new cell
Reducing chromosome number from 2n to n
Telophase I (meiosis)
Membrane forms around each nucleus, 2 nuclei are not identical as each daughter cell contains one member of the chromosome pair.
Meiosis II
Marked by separation of 2 chromatids
Prophase II (meiosis)
Nuclear envelope dissolves and spindle fibres begin to form
Signals beginning of 2nd division
Metaphase II
Chromosome line up at the equatorial plate
Anaphase II (meiosis)
Sister chromatids of each chromosome seperate and move to opposite poles
Telophase II
Second nuclear division is completed, nuclear envelope begins to form around chromosomes, 2nd division of cytoplasm occurs, 4 haploid daughter cells are produced
Mutation
Change in DNA sequence of a gene
Gametic mutation
Mutations can be inherited, parents can pass on genetic mutation to their children if mutation occurs in gamete’s, increasing frequency within population
Somatic mutation
Mutations can be accquired, 2 types
Spontaneous: mutations that arise in nature, no specific agent other than natural processes. Associated w occurance. Eg misetaje occurs when cell copies its DNA before cell division
Induced: mutations that arise from external factors, chemical, exposure, non-naturally occurring radiation exposure, virusus
Eg uv radiation.
Not passed on
2 categories of mutations
Changes in chromosome structure
Changes in number =no disjunction
Deletion
Section of chromosome is deleted, happens in S phase
Eg 22q11, heart defects
Duplication
Section KF a chromosome appears 2 or more times in a row, results in larger number of copies of gene
S ohase
Fragile X syndrome, development issues
Inversion
A section of chromosome is inverted (reversed) during crossing over, no genetic material gained or lost, can alter sequence of a gene making it no longer functional
Chromosome 9, inversion syndrome
Translocation
Swapping a portion of a chromosome with a non-homologous chromosome
Crossing over w nkt its pair
Robertsonian translocation, no visible symptoms
Errors in chromosome number
Non disjunction disorder
When chromosomes are separated during meiosis can cause errors, when 2 homologous chromosomes move to same pole during meiosis or when sister chromatids don’t seperate , when it results in one cell too little it’s called nondisimjumction,
Monosomy
When gamete w 22 chromosomes combines with a normal gamete (23) the zygote will contain 45 chromosomes, only 1 copy of certain chromosome
Trisomy
When gamete w 24 chromosomes combines with a normal gamete the zygote will contain 47 chromosomes, 3 copies of certain chromosomes, normal: 2
What 2 processes occur in meiosis which increase genetic diversity
- Crossing over : in prophase 1, exchange if alleles btw non sister chromatids. Similar alleles transferred
- Independent assortment: occurs when genes from parents are assorted randomly,
different genes separate independently from another,
results in chromosomes lining up randomly,
creates cells w diff combinations of alleles from both maternal and paternal chromosome
Synapsis
When homologous chromosomes come together to cross over (foursome of chromatids) or tetrad
Karyotype
Staining and photographing chromosomes during mitosis, done during pregnancy to test for genetic disorder’s.
2 techniques: cvs (chronic villi sampling) and amniocentesis
CVS: invoked sampling chronic villi which is what connects placenta to mothers uterus lining
Amniocentesis: involves removing from of the the cells that are floating in amniotic fluids
