1. Forms of DNA
DNA changes form during the cell cycle, depending on whether it needs to be used or whether it needs to be moved to a different part of the cell.

2. DNA Basics DNA stands for___________________.
DNA carries the genetic code for an organism
The genetic code is divided into thousands of smaller pieces of information called genes
Each gene has the instructions for making a specific protein
DNA gives the code to RNA, which then builds the protein for the cell
The protein gives an organism one of its traits

3. Genes and Chromosomes
A chromosome is a single long strand of DNA, with many genes connected together
Each chromosome has about 1000 genes on it
Humans normally have 46 chromosomes, 23 from Mom and 23 from Dad – these are the chromosome pairs (PS - other organisms have different numbers of chromosomes)
The chromosomes are numbered by size - number one is the biggest and has the most genes on it
Since the chromosomes come in pairs, every cell has 2 copies of each gene – one came from the mother, the other from the father

4. Which do you have?

5. Storing DNA
Each person has enough DNA in their body that if it was strung together it would reach __________ This means that we need to store it all efficiently.
DNA is wrapped around proteins called histones which act like spools for the DNA thread and these allow the cell to store the DNA in a smaller space.
DNA double helix
DNA filling the nucleus of one cell
DNA wrapped around histone proteins
DNA & histones packed together

6. Chromatin vs. Chromosomes I
Chromatin is found during interphase, when the cell needs to get information from the genes in the DNA.
Chromatin is loose tangles of DNA, like an unwound rope that is being used by a rock climber.

7. Chromatin vs. Chromosomes II
Chromosomes are found during mitosis, when the cell needs to move the DNA from one part of the cell to another.
Chromosomes are wound up strands of DNA, like a rope that is being carried from the car to a cliff by a rock climber.

8. Chromatin vs. Chromosomes III
Chromatin Interphase  UnwoundInvisible Chromosomes Mitosis MovableMicroscopically Visible

9. Chromosome Pairs I
All of your body cells (everything except egg cells and sperm cells) are called “somatic cells.”
Every somatic cell has 2 copies of each chromosome. One copy was inherited from the mother, the other from the father. Humans have ____ pairs of chromosomes in their somatic cells.
These pairs have all the same traits on them, but they can have different versions of each trait.
An “allele” is a specific version of a gene on a chromosome. So the “tongue-rolling” allele is one version of the tongue muscle gene (the other version is the “non-rolling” allele).

10. A “karyotype” – a picture of all the homologous pairs from a person.
Notice there are 2 copies of every chromosome – one of each pair came from the father, the other came from the mother.
ETC.!!!
Tongue-Rolling Allele from Dad
Widow’s Peak Allele from Dad
Non-Rolling Allele from Mom
Widow’s Peak Allele from Mom
The alleles might be different from each other….
…. Or they might be the same!

11. Chromosome Pairs II
The pairs of chromosomes found in your somatic cells are called “homologous pairs,” because they are similar, but not identical (one came from mom, one from dad, they have the same genes but not all the same alleles of the genes).

13. Chromosomes & Cell Division
Before the cell divides, it must copy all of its DNA so that both new cells get a complete copy of the genetic code. This happens during the ____stage of ___________.
When the DNA is copied, it forms identical pairs of chromosomes – they have all the same alleles for every gene. The identical pairs are called “sister chromatids.”
The sister chromatids are held together in the middle at a spot called the centromere. The centromere breaks apart during anaphase, when the sisters separate and go to different daughter cells.

14. Check the matching colors - all alleles are identical
Check the matching colors - all alleles are identical! (Unless they mutated!)
These chromatids were formed by copying the DNA
(known as “replication” during the S stage of interphase.
You copy all of your mom’s and all of your dad’s chromosomes
every time you go through the S stage.