2. DNA = Deoxyribonucleic Acid. Inherited from your parents Genetic material Determines an organism’s traits

3. Double Helix --> twisted ladder Made of nucleotides (building blocks of DNA) Nucleotides have three parts: 1. Deoxyribose sugar unit (Side) 2. Phosphate group (Side) 3. Nitrogenous base (Rungs)

4. 1. Adenine (A) 2. Thymine (T) 3. Cytosine (C) 4. Guanine (G) Always in pairs to form rungs of a ladder A with T & G with C Ladders can UNZIP! Like a ZIPPER! (important in DNA Replication)

6. All organisms: are composed of different proteins have DNA made up of the same 4 nucleotides. So… how can organisms be different if their genetic material is made of the same 4 nucleotides?????

7. By the way the nucleotides are sequenced in DNA Example: A-C-C-T-T-G vs. G-G-C-T-A-T.  (Like the words STREAM and MASTER – both have same letters, BUT different arrangement and meaning) If one tiny mistake occurs in one pair-- > a particular protein will not be made

8. Organisms with very similar sequences are very closely related Example: the chimpanzee and gorilla

9.  Nucleus of cells  Makes up the chromosomes

10.  Long strands of DNA  Each one contains many genes  Homologous pairs  2 chromosomes that look similar & have the same genes Humans = 46 chromosomes (23 pairs) 22 homologous pairs 2 sex chromosomes (Male =XY, Female = XX)

11. Picture of an individual’s chromosome

12. A cell sample is taken & chromosomes are photographed Homologous pairs are matched up Normal Karyotype: 46 chromosomes (22 homologous, 2 sex chromosomes) Can detect chromosomal abnormalities in fetus by amniocentesis Missing, extra, or broken chromosomes

13. Can you see the extra chromosome?....... This one shows an extra chromosome #21 – called trisomy 21. A person with this karyotype has Down’s Syndrome.

14. Chromosome: made of many genes Gene: DNA sequence that codes for a trait Allele: alternate form of a gene Examples: eye color gene has blue, brown, green alleles