BIO 200 Lecture 6 (What Mendel Didn't Know: Genetics)

chromosomes

threadlike structures made of DNA and proteins that carry genetic information

implications of paired chromosomes

chromosomes come in homologous pairs (one from each parent), allowing for recombination and independent assortment

human chromosome counts

23 pairs, 46 chromosomes

karyotypes

picture/map of all chromosomes in a cell, arranged in homologous pairs

chromatids

identical copies of a duplicated chromosome, joined at the centromere

sister chromatids

the two identical chromatids of a duplicated chromosome

centromere

• the region where sister chromatids are joined

• spindle fibers attach here during division

homologous pair

two chromosomes (one maternal, one paternal) with the same genes but possibly different alleles

basics of mitosis and meiosis

• mitosis: produces identical cells for growth and repair

• meiosis: produces gametes (sperm/egg) with half the chromosome number

cell outcomes of mitosis and meiosis

• mitosis: 2 identical diploid cells

• meiosis: 4 unique haploid cells

basic differences between mitosis and meiosis

• mitosis: one division, no crossing over, identical cells

• meiosis: two divisions, crossing over, genetic variation

ploidy

number of copies of chromosomes:

• haploid (1N)

• diploid (2N)

• polyploid (>2N)

sex chromosomes

chromosomes that determine sec (X and Y in humans)

crossing over/recombination

exchange of DNA between homologous chromosomes during meiosis, increasing variation

how chromosomes explain gene linkage

genes close together on the same chromosome tend to be inherited together

how recombination eliminates gene linkage

crossing over can separate linked genes, creating new allele combinations

basics of DNA structure

DNA is a double helix with a sugar-phosphate backbone and paired bases (A-T, C-G)

nucleotides

DNA building blocks: sugar, phosphate, and nitrogenous base (A, T, C, G)

• Adanine (A)

• Thymine (T)

• Cytosine (C)

• Guanine (G)

how does DNA replicate

semi-conservative process: each new DNA molecule has one old strand and one new strand, guided by DNA polymerase

the central dogma

flow of genetic information: DNA → RNA → protein

transcription and translation

• transcription: DNA → RNA (in nucleus)

• translation: RNA → protein (at ribosome)

how are proteins formed?

chains of amino acids assembled by ribosomes according to RNA instructions

can you go from DNA sequence to protein?

not directly from DNA to protein, but DNA codes for RNA, and RNA codons direct amino acid sequence

codons and using the amino acid table

a codon = 3 nucleotides coding for 1 amino acid. The amino acid table helps decode RNA sequences

what do comparisons of protein sequences or DNA tell us about organism relatedness?

species with more similar DNA/protein sequences are more closely related evolutionarily

Watson and Crick

scientists who described the double-helix structure of DNA in 1953