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Chapter 4: Genetics
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Chromosomes, genes, alleles and mutations
How DNA is organized
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Chromosomes = bundles of long strands of DNA
Eukaryotes: minimum 2 chromosomes (associated with proteins)
Humans: 46 chromosomes (associated with proteins)
Prokaryotes: one chromosome (not associated with proteins)

Genes
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Gene = heritable factor controlling a specific characteristic
Genes organized into chromosomes
Variations of genes = alleles
Alleles of same gene occupy locus on each chromosome of a pair
Genome = complete set of an organism's base sequences

Mutations
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Mutation = random, rare change in genetic material
Possible cause: change of the base sequences in DNA
Consequence: different amino acid placed in polypeptide chain
This can have no, little or major effects on the organism
Example: sickle cell anaemia

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Meiosis
Meiosis
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Meiosis = form of cell division, which produces gametes (sex cells) (reduction division)
Each new cell produced by meiosis only has half the number of chromosomes = haploid
cells
Meiosis generates 4 haploid daughter cells

Homologous chromosomes
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Homologous = similar in shape and size, carrying the same genes
In each chromosome pair, chromosomes are homologous
One chromosome from father, one from mother

The phases of meiosis
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Parent must divide twice → 4 daughter cells
Difference to mitosis: crossing over = exchange of genetic material between non-sister
chromatids
Meiosis I → production of two cells with a single set of chromosomes each
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Prophase I
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Chromosomes become visible as DNA becomes more compact
Homologues attracted to each other → pair up
Crossing over
Spindle fibres made from microtubules form

Metaphase I
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Bivalents line up along cell's equator
Nuclear membrane disintegrates

Anaphase I
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Spindle fibres from poles attach to chromosomes and pull them to opposite poles

Telophase I
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Spindles and spindle fibres disintegrate
Chromosomes uncoil and new nuclear membranes form

Cytokinesis, but no S phase
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Dominant alleles are always expressed in a phenotype
Recessive allele: Only has an effect on the if in homozygous state
Codominant alleles: Pairs of alleles that both affect the phenotype when present in a
heterozygote
Locus: Particular position on homologous chromosomes of a gene
Homozygous: Having two identical alleles of a gene
Heterozygous: Having two different alleles of a gene
Carrier: An individual who has a recessive allele of a gene that does not have an effect on
their phenotype

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Multiple alleles
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Sometimes: several alleles for one gene
Ex: Blood type ( book p
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Coli)
To copy a gene, it must be transferred into a plasmid
o Plasmid removed from host cell
o Plasmid cut open using restriction endonuclease
o Gene to be copied is placed into plasmid = gene splicing
o Pasted sing DNA ligase  plasmid now called recombinant plasmid, can be used as
vector
o Vector placed inside host bacterium  put into bioreactor (ideal conditions)
Host cell now copies the gene as it reproduces  can be used for production of insulin (ex
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