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Summary Study Unit 1 Genetics 214
Mitosis & Meiosis, Mendel’s postulates and the various extensions of these,
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GeneticsStudy of how Biological information is stored, transmitted, translated and expressed ->
heredity & variation.
Chromosomal theory of inheritance: Each trait controlled by pair of factors
Heredity & development dependent on (genes).
genetic info residing in genes, contained in • Diploid number (2n): 2 chromosomes.
chromosomes, faithfully transmitted through • Haploid number (n): 1 chromosome.
gametes. • Homologous chromosomes:
chromosomes exists in pairs.
Alleles: alternative forms of same genes. • Mitosis: chromosomes copied &
Phenotypes: different alleles produce distributed as diploid set to each
differences in observable features.
daughter cell (identical).
Genotype: set of homologous copies of alleles
for given trait.
• Meiosis/gamete formation: daughter
Locus: place on chromosome where particular cell receives 1 chromosome from each
gene located. pair = reduction, 2n -> n (not identical).
Trait: genetically determined characteristic due Reduction essential = maintain
to specific genes a chromosome. constant number of chromosomes.
Autosomal genes: are not located on X or Y
chromosomes (not sex dependent). Genetic variation:
Sex dependent: genes carried on X and Y
chromosomes.
Mutation: any heritable change in DNA
sequence & source of all genetic
variation.
Chemical nature of genes
Genes carried on chromosomes -> proteins & RNA, single stranded molecule, with
DNA major chemical components. Uracil instead of thymine.
DNA
Carrier of ALL genetic information. Macro
molecules made up of sugar (deoxyribose),
phosphate & nucleotides:
Uracil = Pyrimidine (1 ring)
• Guanine:
Central dogma
How genes create proteins.
Transcription: in nucleus, where DNA
constructs complimentary RNA sequence
• Cytosine:
(mRNA). mRNA moves to cytoplasm & binds
to ribosomes.
Translation: on ribosomes, where the
genetic code in mRNA consists of codons (3
linear nucleotides). tRNA recognize info
• Adenine:
encoded in mRNA codon & carry proper
amino acids for construction of proteins.
Proteins
Polymers made of 20 different amino acid
• Thymine: monomers & are end products of gene
expression.
Diverse biological functions due to many
different combinations of 20 amino acids.
DNA twisted into double helix, exact Amount of sequences:
complements to on another: 20 n – amount of amino acids.
Enzymes (largest category) used as catalyst
to lower activation energy to allow cellular
metabolism to proceed at body temp.
Guanine & Adenine = Purines (2 rings) M.Smit 22631585@sun.ac.za
Cytosine & Thymine = Pyrimidines (1 ring)
, Chromosomes
Cell & genetic material: Homologous chromosomes: identical in
Plasma membrane: outer covering defining cell length, genetic loci & centromere placement.
boundaries &controls movement of material. • Sex-chromosomes not homo.
Microtubules: fibers of tubulin (protein) +
microfilaments of actin (protein).
Centrioles: organelle made of microtubules, which
organizes microtubules into spindle fibers.
Spindle fiber: lengthen & shorten as addition/loss of
polarized tubulin subunits.
Centrosome: differentiated cytoplasm containing
centrioles.
Chromatin: network of uncoiled chromosomes &
DNA, RNA, histones and other proteins
Centromere: specialized heterochromatic
chromosomal region where sister chromatids
remain attached after replication & where spindle
fibers attach during mitosis/meiosis.
Karyokinesis: nuclear division.
Cytokinesis: cytoplasmic division.
Sister chromatids: genetically identical
chromatids, of same homologous pair.
Biparental inheritance: each sister chromatid
come from maternal & paternal.
Cell cycle
Interphase – G1, S + G2
• Intensive metabolic activity, cell growth &
M Checkpoint:
cell differentiation are evident.
Chromosome • G2 (gap II) end: volume of cell doubled &
G2 Checkpoint:
spindle attached DNA replicated -> mitosis.
Cell size & if
DNA replicated • G2 & S phases lengths are consistent in
correctly all cell types.
• S phase: cohesion forms between sister
chromatids.
• G1 phase length depends on cell.
• G1 point where:
Cell proliferation occurs – initiating DNA
replication.
No proliferation – entering G0 –
withdrawal from cycle, still metabolic
active.
Cancer cell avoid/fast tracks G0.
G1 Checkpoint:
Enough
resources
M.Smit 22631585@sun.ac.za
(nutrients),
growth factors &
DNA damage
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