- Slides: 68
Cell Division Mitosis and Meiosis
Types of Cell Division 1) Mitosis occurs in all body cells (somatic cells) in animals, plants, and humans n production of 2 identical daughter cells that are diploid n growth or replacement of body cells. n asexual reproduction. (offspring and parents are identical)
Types of Cell Division 2) Meiosis occurs only is sex cells (sperm and egg) n production of the 4 non-identical gametes (sex cells) that are haploid n Sperm and eggs have half the genetic information n sexual reproduction n Discovered looking at dividing germ-line cells
The Cell Cycle n n 10% time dividing (mitotic phase/meiotic phase) 90% time interphase (G 1, S, G 2 phases)
Interphase 1) G 1 (gap phase) -manufactures proteins and amino acids needed for both cell processes and cell division, carries out metabolic duties n Cell grows 2) S phase (synthesis phase) – DNA replicates. -longest stage of the cell cycle
3) G 2 (gap phase) n increases the rate of protein synthesis and prepares to divide. n grows larger Cyclins are proteins that help control the cell cycle: Two main types of cyclins: 1) G 1 cyclins: tell the cell to switch from G 1 phase to Sphase 2) MPF- mitosis promoting factors made from cyclins create proteins at this point to initiate/promote cells that are in G 2 to move into mitosis. Once mitosis is complete MPF degrades and the cell goes back into G 1 phase.
Division n Mitosis or Meiosis n cell can divide only about 50 times on average. n To ensure that the cells in a tissue are healthy, cells will undergo a form of cell suicide called apoptosis. n Cell Death
Terms n Chromatin – complex long threads made of DNA and protein that makes up chromosomes n Uncondensed chromosome – long, thin strands not visible with light microscope Condensed chromosome – short and visible n To help chromosomes condense, histone protein complexs will help DNA windup into spools of nucleosomes first and then chromosomes next. Topoisomerase II will help prevent DNA to tangle up while winding. n
Chromosome vs. Chromatid n Chromosomes replicate before division to form 2 matched sister chromatids
Ploidy n Humans have 46 chromosomes (diploid or 2 N) n Sex gametes have 23 chromosomes (haploid or N n Some organisms have polyploidy n Ex) corn – 4 n (tetraploidy)
Homologous chromosomes –same size and shape and carry the genes for the same traits, but have different details n Humans have 23 homologous chromosomes for a total of 46
Gene basic unit of heredity n sequence of nucleotide bases in DNA. n codes for a specific proteins n
n Autosomes – chromosomes that do not influence biological sex (humans have 22 pairs of these) n Sex Chromosomes – X and Y chromosomes that determine biological sex in humans (humans have 1 pair of these, the 23 rd chromosome pair)
Prophase (longest phase) n Early: chromatin condenses to form chromosomes, centrioles move to poles and attach to spindle fibres n Late: spindle fibres attach to centromere, nuclear membrane dissolves
Metaphase n chromosomes line up on the equatorial plate (center of the nucleus)
Anaphase n Spindle fibres contract from the centrioles and sister chromatids begin to separate apart, immediately chromosomes being to unravel
Telophase nucleolus re-appears, nuclear membrane reforms, the chromosomes unravel to form a loose mass of chromatin n cells undergo cytokinesis (divide cytoplasm) n
Plant vs Animal Cells n a cell plate forms between the new daughter cells n the cell membrane pinches in between the two daughter cells
Mitosis Overall n http: //www. loci. wisc. edu/outreach/bioclips/CDBio. html
Some Methods of Asexual Reproduction 1. Binary fission - equal division of both the organism cytoplasm and nucleus to form two identical organisms ex: Protist, amoeba
2) Budding - one parent dividing its nucleus (genetic material) equally, but cytoplasm unequally ex: Fungi- yeast -This is also known as sporulation in yeast
Meiosis – Sexual Cell Division Occurs in sexual reproduction The end result is 4 gamates that are genetically different Spermatagonium 4 sperms
Meiosis I – Reduction Division Prophase I – homologous chromosomes undergo synapsis (pair up) and crossing over occurs. -also, as in mitosis prophase: Chromos condense Nuclear membrane disappears Centrioles move to opposite poles -tetrad
n Metaphase I – homologous pairs line up along the equatorial plate, spindles insert into the centromeres.
n Anaphase I – homologous chromosomes separate and are pulled to opposite poles = segregation
n Chromosomes undergo independent assortment in during Anaphase I -increases genetic diversity
n Telophase I – daughter cells separate, each has one chromosome from each homologous pair. -reduction has occurred so that the new cells will be haploid (n) n -cytokinesis occurs
Meiosis II – like mitosis but no initial replication of DNA -very brief, not as long as meiosis I n Prophase II –spindles form
n Metaphase II –chromosomes align at the equatorial plate
n Anaphase II – the daughter chromatids separate and move towards separate poles
n Telophase II – spindle fibres disappear, nuclei reform and cytokinesis takes place. (All 4 daughter cells are haploid. )
How many genetic combinations of gamates? n The number of possible chromosome combination in a gamate is 2^n n Where ‘n’ is the haploid number n Ex. Humans n=23, thus 2^23 =8, 388, 608 different combinations!! n Now THAT’S diversity!!
n NOVA Online | 18 Ways to Make a Baby | How Cells Divide: Mitosis vs. Meiosis (Flash)
Human Life Cycle
Fern Life Cycle
Oogenesis vs Spermatogenesis n Oogenesis (female) n meiosis II completes only if egg is fertilized Secondary oocyte receives most of the cytoplasm and becomes the egg polar bodies have less cytoplasm and degenerate one egg cell is produced n n Spermatogenesis (male) n meiosis I and II are both completed before fertilization each sperm cell produced receives an equal share of cytoplasm flagellum forms from one of the centrioles four spermatids are produced n n n
Human Karyotype Chart Karyogram: A diagram or photograph of the chromosomes of a cell, arranged in homologous pairs and in a numbered sequence. Karyotype: The characterization of the chromosomal complement of an individual or a species, including number, form, and size of the chromosomes.
Biological Sex n Female is XX n Male is XY XX XY
n Chromosomal abnormalities can be detected by doing a karyotype chart. n Fetal cells are collected through amniocentesis or chorionic villi sampling
Successful cell division relies on 2 things: 1. accurate replication of the chromosomes (during S-phase of interphase) 2. exact separation / distribution of the chromosomes (usualy during anaphase I of meiosis)
n Trisomy –three chromosomes replace a normal pair (47 chromosomes in humans)
Abnormal Meiosis n Non-disjunction – occurs during meiosis when two homologous chromosomes move to the same pole. Chromosomes do not separate properly Normal Division Non-disjunction
Some Common Genetic Disorders **Research shows a higher incidence of these disorder in parents over 40 that have children Down’s syndrome – trisomy 21 n Extra 21 chromosome n more common in children born to women over 40 n characterized by short stature, folds to the eyelids, stubby fingers, wide gap between 1 st and 3 rd toes, large fissured tongue, round head, palm creases, mild to severe mental retardation.
Edward’s syndrome – trisomy 18 n results in severe overall defects with a life expectance of only 10 weeks Patau’s syndrome – trisomy 13 n results in non-functioning eyes, severe deficits and limited life expectancy.
Klinefelter’s syndrome – XXY male n sterile males with underdeveloped testes, overdeveloped breast tissue and sub-normal intelligence
Metafemale – XXX female n no obvious deficits however menstrual irregularities and early menopause are common, some have increase aggression XYY male n taller than normal, recurrent acne
n Monosomy –one chromosome replaces a normal pair (45 chromosomes in humans)
Turner’s syndrome – XO female n females with short stature, broad chest, heart defects, lack of breasts and absence of sexual maturation and menstruation Cri du Chat syndrome n deletion of a portion of one copy of chromosome number 5, malformed face and head, short life
Societal Issues of Cell Division Cloning n identical offspring are formed from a single cell or tissue of the parent. (similar to mitosis) n when plants send out runners, when bacteria divide and in identical twins.
How to Clone: (the quick and easy, yet not so successful way to carry out somatic-cell nuclear transfer) n Take an egg cell from an adult female and remove the nucleus (enucleation). n Replace the nucleus with the nucleus from a body cell of the individual to be cloned. (the cell must be toti-potent, or have its identity genes turned off) (you can use stem cells here)
n Zap it!!! (a little magic is required here) n Implant the zygote or blastula into the mother’s uterus. n Wait until the gestational period is up and voila! n Click and Clone
Dolly n n 1997 -2003 nucleus from udder cell put into egg cell
Problems with cloning: some think it is wrong!!! (ethical issue) n artificially cloned organisms seem to age faster n it is very time and resource consuming and is not guaranteed to work n
Societal Issues Ethical Issues: Issues that deal with right or wrong, beliefs…. not always religion vs science n Economical: Issues that deal with money, expenses, cost vs benefit/time n Socio-economical: issues dealing with class differences n Environmental: Issues dealing with changes to the abiotic or biotic aspects of an ecosystem n
Cell Ageing n the ends of the chromosomes, called telomeres, shorten each time a cell divides, and when they become critically short, the cell dies. Totipotent: when cells reach a certain number of divisions, or age, DNA begins to altered
Cancer n abnormal, uncontrolled cell division. n May be caused due to mutation of genes Tumour suppressor genes – suppress cell division. (mutation turns these off) n Proto-oncogenes – stimulate cell division. (mutation turns these on) n n Telomeres do not shrink in cancerous cells
Why is cancer bad n Cancer cells do not participate in helping the body to function. n Cancer cells require and take away nutrients n Cancer cells can break away (metastasis) from the tumour mass and spread to other parts of the body.
Pandos + Dolly = Pure Bio Magic #dreamcometrue