Chapter 6 and 7 Mitosis and Meiosis

Cell divisions  There are two kinds of cells in a multicellular organism-  BODY CELLS (SOMATIC) these are the cells that make up our bodies  GERM (SEX) CELLS (GAMETES) these are the cells that are used during sexual reproduction  This means that there are two types of divisions  Mitosis- makes new body cells  Meiosis- makes new sex cells  There are two kinds of cells in a multicellular organism-  BODY CELLS (SOMATIC) these are the cells that make up our bodies  GERM (SEX) CELLS (GAMETES) these are the cells that are used during sexual reproduction  This means that there are two types of divisions  Mitosis- makes new body cells  Meiosis- makes new sex cells

Prokaryotic Division  Bacteria and other unicellular organisms reproduce by BINARY FISSION  This means that the organisms duplicate everything inside their cell and then split to form another identical organism  The parent cell and offspring are genetically identical to each other  Bacteria and other unicellular organisms reproduce by BINARY FISSION  This means that the organisms duplicate everything inside their cell and then split to form another identical organism  The parent cell and offspring are genetically identical to each other

Binary Fission

Eukaryotic cell division  All the DNA and other organelles must be duplicated  GENE- a segment of a chromosome made of DNA that codes for certain traits, proteins, or RNA  CHROMOSOME- the linear, coiled segments made of DNA, these contain all of our genes  CHROMATIDS- each half of a chromosome  CENTROMERE- the point where two chromatids attach to each other  All the DNA and other organelles must be duplicated  GENE- a segment of a chromosome made of DNA that codes for certain traits, proteins, or RNA  CHROMOSOME- the linear, coiled segments made of DNA, these contain all of our genes  CHROMATIDS- each half of a chromosome  CENTROMERE- the point where two chromatids attach to each other

Chromosome numbers  Every organism has a specific number of chromosomes- for humans it is 46  Our 46 chromosomes are made of 23 pairs of matching chromosomes called HOMOLOGOUS chromosomes  We get 23 chromosomes from each parent that pair up to determine what we are like  DIPLOID- cells that have all their chromosomes 46 (23 pair) 2n  HAPLOID- cell that have half their chromosomes 23 (n)  ZYGOTE- the new cell formed after fertilization  Every organism has a specific number of chromosomes- for humans it is 46  Our 46 chromosomes are made of 23 pairs of matching chromosomes called HOMOLOGOUS chromosomes  We get 23 chromosomes from each parent that pair up to determine what we are like  DIPLOID- cells that have all their chromosomes 46 (23 pair) 2n  HAPLOID- cell that have half their chromosomes 23 (n)  ZYGOTE- the new cell formed after fertilization

Chromosomes

 We have 23 pairs of chromosomes- these contain the genes that make us who we are.  Chromosome pairs 1-22 are called AUTOSOMES- these determine all of our traits EXCEPT our sex  The 23 rd pair of chromosomes are called the SEX CHROMSOMES- these determine our sex  XX = girl  XY= Boy  Remember you will get one sex chromosome from each parent- so who determine the sex of a child?  We have 23 pairs of chromosomes- these contain the genes that make us who we are.  Chromosome pairs 1-22 are called AUTOSOMES- these determine all of our traits EXCEPT our sex  The 23 rd pair of chromosomes are called the SEX CHROMSOMES- these determine our sex  XX = girl  XY= Boy  Remember you will get one sex chromosome from each parent- so who determine the sex of a child?

Female and male karyotypes

Changes in chromosome numbers  Occasionally mistakes occur and a person gets too many chromosomes or not enough chromosomes- these will be discussed later in your genetic disorder projects  In order to determine if this is the case a KARYOTYPE will be made- this is a photo taken during mitosis that shows all the chromosomes  NONDISJUNCTION- the failure of chromosomes to separate causing a sex cell to have too many or too few chromosomes  Occasionally mistakes occur and a person gets too many chromosomes or not enough chromosomes- these will be discussed later in your genetic disorder projects  In order to determine if this is the case a KARYOTYPE will be made- this is a photo taken during mitosis that shows all the chromosomes  NONDISJUNCTION- the failure of chromosomes to separate causing a sex cell to have too many or too few chromosomes

CELL CYLE  The life cycle of a cell starting with a new cell and ending with cell division  3 Stages  INTERPHASE- the majority of a cell’ life  MITOSIS- division of the nucleus  CYTOKINESIS- the division of the cell membrane and other cellular parts  The life cycle of a cell starting with a new cell and ending with cell division  3 Stages  INTERPHASE- the majority of a cell’ life  MITOSIS- division of the nucleus  CYTOKINESIS- the division of the cell membrane and other cellular parts

Cell cycle

INTERPHASE  90% of the cells life  3 phases  G1 phase- this is where a cell grows and carries out its normal routine. If all is correct it will pass the G1 checkpoint  S phase- this is where all the DNA in the nucleus is copied. If all is correct it will pass the G2 checkpoint  G2 phase- the cell will prepare for division. If all is correct it will pass the Mitosis checkpoint  90% of the cells life  3 phases  G1 phase- this is where a cell grows and carries out its normal routine. If all is correct it will pass the G1 checkpoint  S phase- this is where all the DNA in the nucleus is copied. If all is correct it will pass the G2 checkpoint  G2 phase- the cell will prepare for division. If all is correct it will pass the Mitosis checkpoint

Loss of Control  If things go wrong during interphase, the cell may not be able to control mitosis  This will lead to uncontrolled division of a cell  Uncontrolled growth and division of a cell can lead to CANCER  If things go wrong during interphase, the cell may not be able to control mitosis  This will lead to uncontrolled division of a cell  Uncontrolled growth and division of a cell can lead to CANCER

MITOSIS  Phases of mitosis  PROPHASE  METAPHASE  ANAPHASE  TELOPHASE  CYTOKINESIS- division of cell membrane- most often is combined with Telophase  Phases of mitosis  PROPHASE  METAPHASE  ANAPHASE  TELOPHASE  CYTOKINESIS- division of cell membrane- most often is combined with Telophase

PROPHASE  Chromsomes condense and become visible. Nucleus dissolves. Centrioles move to opposite ends of cell. Spindle fibers form

METAPHASE  Chromosomes line up along center of cell (equator). Spindle fibers attach to chromosomes

ANAPHASE  Spindle fibers begin to shorten. Chromosomes separate and begin to move to opposite ends of cell.

TELOPHASE  Chromosomes at opposite ends. Nucleus reforms. Chromosomes uncoil. Spindle dissolves. Cytokinesis begins.

CYTOKINESIS  Cell membrane pinches together at the CLEAVAGE FURROW. Cells continue to separate. In plant cells a CELL PLATE forms across the cell eventually forming a new cell wall.

MEIOSIS  Has the same phases as mitosis, however there are 2 divisions of the nucleus resulting in 4 cells being produced.  The DNA is only copied once resulting in cells that have only half the information (n)  This makes Germ cells (gametes)  The resulting cells are unique from each other  Has the same phases as mitosis, however there are 2 divisions of the nucleus resulting in 4 cells being produced.  The DNA is only copied once resulting in cells that have only half the information (n)  This makes Germ cells (gametes)  The resulting cells are unique from each other

Meiosis

Phases of Meiosis  Meiosis I  Prophase I  Metaphase I  Anaphase I  Telophasse I  Meiosis II  Prophase II  Metaphase II  Anaphase II  Telophase II  Meiosis I  Prophase I  Metaphase I  Anaphase I  Telophasse I  Meiosis II  Prophase II  Metaphase II  Anaphase II  Telophase II

PROPHASE I  Chromosomes condense. Nucleus dissolves. Spindles form. Centrioles move.  Crossing over occurs  Chromosomes condense. Nucleus dissolves. Spindles form. Centrioles move.  Crossing over occurs

Crossing Over

METAPHASE I  Chromosomes line up randomly along equator. Spindles attach.

ANAPHASE I  Chromosomes move to opposite ends of cell.

TELOPHASE I and CYTOKINESIS  Chromosomes reach opposite ends of cell. Nucleus reforms. Cytokinesis divides the cell.

PROPHASE II  Cell DOES NOT COPY the DNA. New spindle forms, centrioles move, nucleus dissolves, crossing-over DOES NOT occur

METAPHASE II  Chromosomes linje up randomly along equator. Spindles attach.

ANAPHASE II  Chromatids (1/2 of chromosome) divide randomly and begin to move to opposite ends of the cell.

TELOPHASE II and CYTOKINESIS  Chromatids reach opposite ends of cell, nucleus reforms, cell divides.  The cells that form have ½ of the original chromosomes  Chromatids reach opposite ends of cell, nucleus reforms, cell divides.  The cells that form have ½ of the original chromosomes

GAMETOGENESIS  The four haploid cells that form will develop into gametes  SPERMATOGENESIS- in males all 4 haploid cells will develop into sperm cells  OOGENESIS- in females cells divide unevenly during cytokinesis. At the end of meiosis I there is a polar body and a secondary egg cell. The polar body will divide into two polar bodies and the egg cell will divide into an egg cell and a third polar body.  Polar bodies die. Egg will continue to develop into an egg  The four haploid cells that form will develop into gametes  SPERMATOGENESIS- in males all 4 haploid cells will develop into sperm cells  OOGENESIS- in females cells divide unevenly during cytokinesis. At the end of meiosis I there is a polar body and a secondary egg cell. The polar body will divide into two polar bodies and the egg cell will divide into an egg cell and a third polar body.  Polar bodies die. Egg will continue to develop into an egg

Gametogenesis

VARIATION  The resulting cells that form from meiosis are all unique in the genetic information that they have.  Crossing-over reshuffles parts of chromosomes creating unique chromosomes  Independent assortment- this means that chromosomes will randomly line up and then be randomly divided during meiosis  Random fertilization- human male will produce over 100 million sperm daily and will use millions during sex. What are the odds that a sperm will carry the exact copy of chromosomes that made you? What are the odds that an egg was made exactly the same.  The resulting cells that form from meiosis are all unique in the genetic information that they have.  Crossing-over reshuffles parts of chromosomes creating unique chromosomes  Independent assortment- this means that chromosomes will randomly line up and then be randomly divided during meiosis  Random fertilization- human male will produce over 100 million sperm daily and will use millions during sex. What are the odds that a sperm will carry the exact copy of chromosomes that made you? What are the odds that an egg was made exactly the same.

Random fertilization

Variation  Think of a deck of cards. There are black pairs of cards and red pairs of cards. If I shuffled the cards and dealt you pairs of cards from 2-Ace, what are the odds that you would get exactly all the same cards if I did it again. How many times would I have to deal the cards for that to happen?

Why is variation important?  Variation is the driving force in natural selection.  If all organisms are identical will a species evolve?  Variation allows for individuals to be unique.  Some of the organisms will be dealt good combinations of genes, others will be dealt bad combinations.  If conditions change, then variation allows for organisms to be better adapted to those changes.  Variation is the driving force in natural selection.  If all organisms are identical will a species evolve?  Variation allows for individuals to be unique.  Some of the organisms will be dealt good combinations of genes, others will be dealt bad combinations.  If conditions change, then variation allows for organisms to be better adapted to those changes.