Lecture 1, 2

Lecture Overview

• Review of basic concepts from molecular biology and genetics.

• Important for students familiar with college-level biology or AP Biology.

• Focus on definitions like loci, alleles, and recombination.

DNA Structure

• Human body contains ~37.2 trillion cells, each carrying genetic information.

• Genetic info is in deoxyribonucleic acid (DNA), composed of nucleotides:

  • Adenine (A)

  • Thymine (T)

  • Cytosine (C)

  • Guanine (G)

• DNA is a double-stranded molecule; base pairing is:

  • A pairs with T

  • C pairs with G

• Human genome: 3.2 billion nucleotides (or base pairs).

Chromosomes

• DNA is organized into 23 chromosomes in humans.

• Chromosomes visible during certain life-cycle phases, composed of DNA and proteins.

• Chromosomes are located in the nucleus; the rest of the cell is cytoplasm.

Proteins

• Proteins perform cellular functions, made up of amino acids (22 types).

• Structure determines function; examples include:

  • Hemoglobin for oxygen transport.

  • Lactase for lactose digestion (enzyme).

DNA to Protein: Transcription and Translation

• Transcription: DNA to RNA; RNA is single-stranded (thymine replaced by uracil).

  • Production includes mRNA (messenger RNA).

• Translation: mRNA to protein at ribosomes.

  • Codons (3 nucleotides) code for amino acids; start (AUG) and stop codons defined.

Genes and Gene Expression

• Protein coding genes (~20,000 in the human genome) include:

  • Exons (coding segments)

  • Introns (non-coding segments)

• Gene expression regulated by transcription factors.

Loci and Alleles

• Diploid organisms (e.g., humans) have two copies of DNA (one from each parent).

• Loci are positions in the genome; alleles are specific versions of genes.

• Polymorphism: presence of different alleles at a locus.

Genotypes

• Genotype: combination of alleles at a locus.

  • Homozygous: two identical alleles.

  • Heterozygous: two different alleles.

Mutations and Meiosis

• Mutations are errors during DNA replication; common types are:

  • Point mutations: single nucleotide changes.

• Meiosis produces haploid gametes (egg and sperm) from diploid cells.

Mendel’s Laws of Genetics

• Law of Segregation: alleles segregate during gamete formation.

• Law of Independent Assortment: alleles at different loci assort independently.

• Phenotypes are observable traits.

Genetic Drift and Population Genetics

• Genetic drift: random changes in allele frequencies, significant in small populations.

• Drift can lead to fixation (allele frequency of 1) or loss (allele frequency of 0).

• Founder effect: reduced genetic variability in small populations.

Conclusion

• Allele frequencies change due to various factors including genetic drift and mutations.

• Understanding of allele transmission essential in population genetics and evolutionary studies.