Chromosomes: the genetic material of the cells is organized into chromosomes
Chromatin: chromosomes contain chromatin, chromatin is a combination of proteins and DNA
Most human cells are diploid meaning chromosomes occur in pairs
Prior to mitosis the chromosomes are replicated forming sister chromatids connected by a centromere
Karyotype: a visual display of someone’s chromosomes
The cell cycle: occurs continuously and has four stages G1 S G2 … the interphase stages and M the meiotic phases cytokinesis and the stage of mitosis
In G1: a cell doubles organelles accumulates materials for DNA synthesis
In S: DNA replication occurs
In G2: a cell synthesizes proteins needed for cell division
Checkpoints: control the progression of the cell cycle cells cycle. Cells that fail to pass the checkpoints may undergo apoptosis( G0) protein p53 can stop cell
Mitosis; duplication division that insures that the daughter cells have the diploid (2n) number same as the parent cell
Mitotic spindle: important role in the separation of the sister chromatids during mitosis
Centrosomes: organizes the mitotic spindles and contain clusters of microtubules called centrioles
Mitosis phases:
PROPHASE: Chromosome attach to spinal fibers
METAPHASE: Chromosomes Align at the equator
ANAPHASE: Chromatids separate becoming chromosomes that moves towards the poles
TELOPHASE: nuclear envelopes form around chromosome and cytokinesis begins
Cytokinesis in animal cells involves cleavage farrow to separate the cytoplasm
Meiosis: is a reduction division reduces the diploid from 2n to n haploid number.
Meiosis I: homologous chromosomes pair and the separate. Interkinesis follows meiosis I
Meiosis II : sister chromatids separate, resulting in four cells with haploid number of chromosomes that move into daughter nuclei
Cross over: meiosis results in genetic recombination
Spermatogenesis and oogenesis
Spermatogenesis: in males produces four viable sperms
Oogenesis : in females produces one egg and several polar bodies
Comparison of mitosis and meiosis
In prophase I homologous chromosomes pair there is no pairing in mitosis
In metaphase I homologous duplication chromosomes align at the equator
Nondisjunction: change the chromosome number in gametes resulting in trisomy or monosomy
Numerical vs structural abnormalities
Trisomy 21
Turner syndrome
XXY
XYY
Humans have 46 chromosomes
Chromosomal abnormalities happen as a result of error in one or more of the following meiosis, mitosis, maternal aging, and environment
Egg with 23 chromosomes … sperm with 23 chromosomes… create zygote with 46 chromosomes
Mitosis = zygote with 46 chromosomes creates two cells with 46 chromosomes
Meiosis cell with 46 chromosomes creates four gametes with 23 chromosomes each
more than two chromosomes of a pair- trisomy
Trisomy 21 down syndrome
46 chromosomes
structural abnormalities deletion – a portion of the chromosome is missing or deleted duplication- a portion of the chromosome is duplicated resolution in extra genetic material translocation- when a portion of one chromosome is transferred to another chromosome inversions: a portion of the chromosome has broken off turned upsidedown and re attached rings: a portion of the chromosome has broken off and formed a circle ring this can happen with or without loss f genetic material down syndrome occurs in 1 in 800 births in Canada it has extra genetic material associated with the 21st chromosome. (just an extra chromosome on the 21st)
-flattened nasal bridge
-small mouth
-thin upper lip
-enlarged tongue
-low muscle tone fifth finger only has one flexion furrow
health concerns heart defects leukemia underactive thyroid frequent infections
