Genes and DNA What are we really talking about????

1. Genes and DNAWhat are we really talking about????

2. Chromosome Structure

3. DNA • DNA is a double-stranded • Forms a helix (twisting structure) • Made up of a phosphate group, a sugar, and 4 different nucleotide bases

4. DNA • Looks like a twisted ladder • Sides of the ladder = backbone of the DNA molecule consists of the phosphate and sugar groups

5. DNA • Rungs of the ladder = nucleotide bases • 4 bases are: • Adenine (A) • Guanine (G) • Thymine (T) • Cytosine (C) Rungs are formed from complimentary base pairing – T always joins to A, C always joins with G on opposite strands

6. Homologous Chromosomes • Homologous chromosomes are pairs of chromosomes that are similar in length, centromere location, and banding pattern • One is from the female, other from the male

7. Homologous Chromosomes • Homologous chromosomes contain the same sequence of genes • Doesn’t mean they contain the exact same alleles for each gene  so they are not identical!

8. Wait – what’s a gene?What’s an allele? • Gene – a section of DNA that contains genetic information for the inheritance of specific traits • Allele – different forms of the same gene (i.e. Alternate versions of the same gene, e.g., gene for brown hair, gene for blonde hair, gene for black hair are all alleles for hair colour) • Genome – the complete DNA sequence of an organism • Human Genome Project

9. Karyotype • A pictorial representation of the set of chromosomes that an individual has • Most humans have 23 pairs of homologous chromosomes in their karyotype

10. Karyotype • 22 of the pairs are autosomes • Autosomes are chromosomes not involved in determining the sex of the organism • 1 pair = sex chromosomes • XX = female • XY = male