dna = deoxyribonucleic acid. inherited from your parents genetic material determines an organism’s...
Post on 23-Dec-2015
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INTRODUCTION TO DNA AND CHROMOSOMES
DNA: What is IT?
• DNA = Deoxyribonucleic Acid.• Inherited from your parents• Genetic material• Determines an organism’s traits
DNA Structure
• 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 Different Nitrogen Bases:
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)
Importance of Nucleotide Sequences
• 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?????
How Do Organisms Differ?
• 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
Organisms with Similar DNA
• Organisms with very similar sequences are very closely related• Example: the chimpanzee and gorilla
Where is DNA Found?
Nucleus of cells Makes up the chromosomes
Chromosomes 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)
Karyotyping:
• Picture of an individual’s chromosome
More on Karyotyping
• 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
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.
CHROMOSOMES versus GENES?
• 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
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