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Biology Level
AP Biology Level
Cell Cycle, Mitosis, and Meiosis
Chromosomes, Genes, and Mitosis
Each human chromosome is made up of only one double helix strand of DNA. Each one has between 50 million and 250 million nucleotides. One human DNA strand stretched out would be between 0.6 inches and 3.0 inches long (15-75 millimeters) All the DNA in one nucleus would stretch 6 feet (1.8 meters)
In order to get all of this genetic information to fit into a microscopic cell nucleus the DNA strand needs to be wound very compactly.
Genes
A gene is a segment of DNA that codes for a specific trait
-A trait is a characteristic that is inheritable
-The specific location of a gene on the DNA is called a locus (loci for plural)
-Different chromosomes contain different amounts of genes
-The largest human chromosome is chromosome 1
-It has more than 3,000 genes on it
-The smallest human chromosome is chromosome 22
-It has about 600 genes on it
A Karyotype is a picture of all of an individuals chromosomes
Different species have different amounts of chromosomes
In each cell
-A human has 23 pairs of chromosomes
-A Human has 46 chromosomes all together
-Even though a human has 46 they only have 23 different ones since a human has two of each chromosome. One set from mom one set from dad.
-Chromosomes that contain the same genes are called homologous chromosomes
-Just because they have the same genes does not mean that they are identical
-They have the same genes but they have different alleles (different versions of those genes)
Diploid and Haploid
-If an organism or cell has two of every chromosome it is called Diploid (Meaning Double)
-Diploid organisms receive one set from each parent
-Humans are a diploid organism
-An organism or cell that only has one of every chromosome is called Haploid (Meaning Half)
-There are some organisms that are haploid and usually reproduce asexually
-Gametes are haploid cells because they will fuse with another haploid and become a diploid cell
-Humans have two different types of cells
-Gametes- sex cells like sperm and eggs which are haploid and contain half of your DNA
-Somatic cells-body cells which are diploid and contain all of your DNA
Chromosomes
-There are autosomes which are chromosomes that both males and females have in common
-And then there are sex chromosomes that are different depending if you are male or female
-In mammals the sex chromosomes are X and Y
-The X chromosome is the female chromosome and the Y chromosome is the male chromosome
-If you have a Y chromosome you are male
-XX= Female and XY=Male
-Sex chromosomes are different for different animals
-Birds have a ZW
ZZ=Male and ZW=Female
-Some insects like ants have diploid females and haploid males
XX=Female and X=Male
-Chromosomes have different parts
-Gene Locus
Mitosis
The Cell Cycle
-Interphase is the normal growth and living stage of a cell
There are 3 steps to interphase.
-G1 is the first growth stage where a cell grows
-S phase is the synthesis stage. This is the time that a cell starts copying all of its DNA so when it comes time to divide it will have a copy for both cells
-G2 is the 2nd growth stage where the cell grows for the purpose of division.
There are checks before many of the stages can continue
-Prophase is the first phase is division. During prophase the nucleus breaks apart and the chromatin condenses into chromosomes. The chromosomes then begin to get pulled to the center of the cell
-Metaphase is when the chromosomes are all aligned in the middle of the cell
-Anaphase is when the sister chromatids are being pulled apart to opposite ends of the cell
-Telephase is when 2 nuclei start to form around the separated chromatids, the chromatids unwind, and cytokinesis begins to split the cell
Mitosis
With sexual reproduction
-There are two gametes that fuss together. This makes a genetically different organism
-During mitosis the two cells are genetically identical but with sexual reproduction two different genetic codes come together
-Both the egg and sperm are haploid having only one set of chromosomes
-When they come together they make one diploid cell
-When the egg and sperm fuse together that cell is called a zygote
-That cell then starts dividing through mitosis growing into a fetus
As we will learn the most important aspect of sexual reproduction in a biological sense is that it creates diversity
Cloning
Cloning is a type of asexual reproduction where the offspring is genetically identical to the parent
How do we make clones?
Lets talk about Dolly!
Can this be done with any type of animal
-For the most part yes!
How about a human?
Could we make a wooly mammoth?
Stem Cell Research
-Lets write on the board
-What do you think stem cell research is?
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