Classical and Modern Genetics

1. Classical and Modern Genetics

2. Classical and Modern Genetics • “Genetics”: study of how biological information is carried from one generation to the next • Classical • Laws of inheritance developed from observations of Gregor Mendel (1800’s) • Modern • Studies of how genes pass information from parent to offspring on the basis of molecular chemistry (1950 to present).

3. Classical and Modern Genetics • Classical (beginning in the 1800’s) • Mendel observed traits in pea plants being passed from parent to offspring via “unit of inheritance” • Observed traits could be dominant or recessive • Dominant traits expressed even if only present in one parent • Recessive traits expressed only if neither parent has the dominant trait • Tested crosses in pea plants • Tested in both 1-trait and 2-trait crosses

4. Classical and Modern Genetics • When studying genetic crosses must distinguish between genotype and phenotype for a particular trait: • Example: tall (dominant) / short (recessive)

5. Classical and Modern Genetics • Mendel’s test crosses - Cross-pollinated purebred and hybrid plants to observe offspring • If parents are pure for a single trait: • Female: TT • Male: tt • All four possible offspring in first generation look “tall” but are hybrid Tt • If cross hybrids above: • Female: Tt • Male: Tt • 3 of 4 possible offspring in second generation look tall and 1 of 4 looks short. One of tall is pure TT, Two of tall are hybrid Tt, The one short is pure tt.

6. Classical and Modern Genetics • Modern (beginning in the 1950’s) • Mendel’s “units of inheritance” recognized as “genes” • Genes located on chromosomes • Chromosomes present in pairs in nucleus of eukaryotic cells • Chromosomes contain nucleic acids which code for all inheritance

7. Classical and Modern Genetics • Human Chromosomes • A total of 46 chromosomes (23 pairs) • All cells have 46 chromosomes except reproductive cells • Reproductive cells have just 23 – one member of each pair • 22 pairs are “autosomes” and 1 pair is the “sex chromosome pair” • Males have the sex chromosome XY, Females have XX

8. Classical and Modern Genetics • Nucleic Acids • 4th category of organic molecules • Include DNA, RNA, (and ATP) • Large polymers made from chain of monomers • Monomer unit = nucleotide • Sugar • Phosphate group • Base

9. Classical and Modern Genetics • DNA • Double strand in helix formation • Described by Watson and Crick (1953) • DNA nucleotides contain • Sugar • deoxyribose • Phosphate group • Base • A, Adenine • T, Thymine • C, Cytosine • G, Guanine • Base pairs include • A-T, T-A, C-G, G-C • Sequence of bases determines genetic code

10. Classical and Modern Genetics • RNA • Uses code from DNA to direct production of protein by the cell • Single strand nucleic acid • Nucleotide contains • Sugar • Ribose • Phosphate group • Base • A, Adenine • U, Uracil (instead of thymine as found in DNA) • C, Cytosine • G, Guanine • Three different types: mRNA, tRNA, rRNA

11. Classical and Modern Genetics • Transcription of DNA message • Method by which coded DNA message is read by RNA • mRNA (messenger RNA) copies a specific DNA sequence and carries it from the nucleus to the ribosomes

12. Classical and Modern Genetics • Translation of message into a protein • A “codon” (set of three bases) on the mRNA is read by a tRNA (transfer RNA) which picks up the proper amino acid for the code and brings it to the ribosome • Protein synthesis (joining the correct amino acids together) occurs at the ribosomes

13. Classical and Modern Genetics • Definitions • Genetic code • Correspondence between base pair sequences and amino acids • Mutation • Error in the coded sequence • Genome • Complete description of an organisms genetic code • Mapping • Position of every gene on every chromosome • Sequencing • Exact order of base pairs on every gene Human genome has 3 billion base pair sequences!