Unit A, Lesson 7: Mitosis, Meiosis, and Fertilization

The symbolic representation of being haploid

1n

The symbolic representation of being diploid

2n

A molecule that is double helix in shape and contains the genetic information needed for the development and functioning of all known living organisms

DNA

-replicating DNA -carrying it's cells processes -occurs 90% of the time

Interphase

-the process that creates gametes (egg and sperm cells), and each cell that is created is unique. -The process used to create sex cells; a two-stage division process that results in four cells that have half the number of chromosomes as the original cell -human sperm and egg cells each have 23 chromosomes. making 46 chromosome altogether. -reduction division: starting human cells is 46 and is reduced to 23 cells. - each cell is unique. -all sperm cells are different.

Meiosis

-an important process that is used by all living organisms. In our bodies it is used for growth and for repairing injuries. -Mitosis = cell division done by body cells -Mitosis makes identical cells -occurs 10% of the time -Cells are not dividing all the time -Mitosis is not a process that makes sperm or egg cells (THAT IS MEIOSIS!)

Mitosis

-Meiosis starts off in the same way that mitosis does. The cells in the reproductive organs will replicate the DNA to form the X shape. The membrane surrounding the nucleus will dissolve and the chromosomes will begin to pair up. This is where meiosis begins to differ from mitosis. -a human has 46 chromosomes. Each chromosome has a matching pair; it is the same chromosome with the same genes, but variations in those genes. For example, the length of your ring finger when compared to your middle finger is controlled by a gene on one chromosome. There are two variations of this gene and both variations are located in the same spot on the same chromosome. Since a person has two copies of each chromosome, they can also have both variations of the gene. -These chromosomes are not exactly alike because they have different variations, but they are still the same chromosome because they contain the same genes. This pair is called homologous chromosomes.

What comes before Meiosis?

chromosomes, and DNA, are always found in the nucleus of a cell (the brain of the cell). -This nucleus will only use the information it needs from the DNA, but will contain all 46 chromosomes. This acts as a kind of back-up system for our genetic material.

Where are chromosomes and DNA always found?

The production of genetically identical offspring from one individual

asexual reproduction

-At the DNA level, once a cell gets large enough to divide, the chromosomes replicate themselves. -These replicated chromosomes then look like Xs, with each leg of the X being one copy of the chromosome. During this time the membrane (border) around the nucleus will dissolve to allow the chromosomes more room.

before mitosis begins

It is very unlikely for any gamete to have the exact same genetic information, and this is why siblings are always different from each other. The only exception is identical twins because they are formed from the same fertilized egg and so have the same genetic information.

can different gametes have the same genetic info?

Chromosomes are strands of DNA that contain many genes. -A threadlike structure that contains DNA and proteins and is found in the nucleus of most living cells. It becomes X-shaped when it duplicates. -Each chromosome contains specific genes -A typical human has 23 pairs of chromosomes-each pair consists of one chromosome from the mother and one chromosome from the father-for a total of 46 chromosomes. -Each pair of chromosomes will have the same genes, however they may have slight variations depending on the information that each parent passed down. -A karyotype will show all the chromosomes matched up in their pairs. -Chromosomes are actually made up of DNA that has been wrapped around specific proteins called histones. These histones act as spools to wrap the DNA around. -Chromatin is the name used for this combination of DNA and proteins that make up chromosomes.

chromosomes

-The two identical cells that are cerated through mitosis -daughter cells grow until they get big enough to divide into their own daughter cells. -This growing and dividing occurs constantly in your body and is known as asexual reproduction.

daughter cells

A cell that has the normal amount of chromosomes. It has pairs of homologous chromosomes.

diploid

-The process where two sex cells join to create one cell with the normal number of chromosomes. This is the process that forms a baby. -when a male gamete cell (in humans, the sperm cell) and a female gamete cell (in humans, the egg cell) join together to create a cell with two sets of chromosomes, a diploid cell. -Once it becomes a diploid cell, it can undergo mitosis, just like a regular somatic cell, to grow and start developing. This is the process that creates offspring through sexual reproduction. -Before fertilization , we have two gamete cells created by meiosis, one from the mother and one from the father. Remember that gamete cells are haploid cells. -Once the two gamete cells have combined into one cell, the new cell has two copies of the chromosomes, one from the mother and one from the father. -This cell is now a diploid cell because it has two copies of each chromosome. -The main advantage to sexual reproduction is that unique offspring are produced. With a full set of chromosomes, there can be over 70 trillion possible genetic combinations. That means that even if an organism had 70 trillion offspring, no two would be alike! The exception to this would be identical twins.

fertilization

The sex (sperm and eggs) cells in a living organism. These are haploid cells and are used in sexual reproduction.

gametes

A segment of DNA that carries the instructions for the creation of one protein

genes

A cell that has only half of the normal amount of chromosomes. It has only one copy from each pair of homologous chromosomes.

haploid cell

A pair of chromosomes that would be matched during a karyotype because they have the same length, centre point, and genes. In humans, one of these chromosomes would come from the individual's mother and the other from their father.

homologous chromosomes

-An image that organizes the chromosomes of a cell according to the chromosome number.

karyotype

-Mitosis: repairs damage, makes body cells, makes identical cells, helps with growth. -Meiosis: does not make identical cells, sperm and egg cells. -One way to remember the difference is that mitosis—mi-t(w)o-sis—ends with diploid (2n) cells that have two copies of the chromosomes, while meiosis—mei-o(ne)-sis—ends with haploid (1n) cells that have one copy of the chromosomes.

mitosis vs meiosis

liver cells do not need to grow and divide quite as fast as skin cells

rate of growth of liver cells

Nerve cells are also a type of somatic cell, however they never divide. Once a nerve cell dies, it will not be replaced.

rate of growth of nerve cells

Skin cells are constantly dying and being replaced as they are our first defence against the outside world

rate of growth of skin cells

The production of offspring by combining genetic information from two individuals of different sexes

sexual reproduction

-Any type of cell in a living organism other than the sex cells. -Your body creates new cells to stack on the old ones (like building blocks) or to replace damaged ones. -This is how you grow and heal -These building block cells are called somatic cells (body cells) and mitosis is the process that creates new somatic cells. -Just like any other living thing, somatic cells grow as they get older. -Once a cell gets big enough, it will divide itself into two new identical cells. -These new identical cells are called daughter cells. -Each type of somatic cell will grow at a different rate. For example, a liver cell will grow at a slower rate than a skin cell.

somatic cells

-step 1 At this stage in meiosis, the homologous chromosomes pair up and line up down the centre of the cell. -step 2 Once the homologous chromosomes are in line, each pair will split and the duplicate chromosomes will move to opposite sides of the cell. -step 3 Then the cell will split off and divide into two cells. These cells are not identical to their parent cells because they do not have two pairs of each chromosome, instead they have one chromosome from each pair in its replicated X form. -step 4 Now the replicated chromosomes will line up down the middle of their respective cells. -step 5 Once they have lined up, the replicated chromosomes will split, with one copy going to each side of the cell. -step 6 Now each of the cells will divide into two cells, creating four new cells. -These cells are special because they only have one of the homologous chromosomes—this means they have half the number of chromosomes as a regular cell! This type of cell is called a haploid cell — remember ha(lf)ploid cell—and it is symbolized by 1n. A somatic cell is called a diploid cell — remember di(meaning two)ploid cell-and it is symbolized by 2n.

steps of MEIOSIS

-Step 1 Once the chromosomes have replicated they will move to line up at along the centre of the parent cell. -Step 2 Once they are in line, the replicated chromosomes are pulled apart and move to opposite ends of the cell. -Step 3 The cell then begins to pinch off and becomes two new cells. -Step 4 The chromosomes then move back to the centre and into the nucleus of the new daughter cell -Each cell has one copy of the replicated chromosomes. -Since the replicated chromosomes have been split between the new daughter cells and are no longer replicated, they will no longer have the X shape. -Both the parent cell and the daughter cells contain pairs of chromosomes, meaning that there is material from both parents. -When there are two copies of each chromosome, the cell is considered to be diploid.

steps of MITOSIS