Summary
Summary Genetics
- Module
- IB Biology
- Institution
- Peter Symonds College Winchester
Genetics notes, including inheritance patterns, genetic diseases, meiosis, and genetic engineering.
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➔ Metabolism: web of all the enzyme-catalysed reactions in a cell or organism➔ Anabolism: synthesis of complex molecules from simpler molecules including formation of
macromolecules from monomers by condensation reactions
➔ Catabolism: breakdown of complex molecules into simpler molecules including hydrolysis
of macromolecules into monomers
GENETICS
➔ Genes: sequence of bases found on chromosomes - heritable factor influencing a specific
characteristic
◆ gene locus: specific gene position on chromosome
◆ Centromere is section with no genes
➔ Chromosomes: DNA wrapped around histone protein
◆ Number of chromosomes is characteristic feature of members of a species
➔ Homologous chromosomes: carry the same sequence of genes
◆ Not necessarily same alleles or base pair sequence
➔ Diploid cells’ nuclei carry pairs of homologous chromosomes
◆ 2n
◆ all somatic cells (body cells) are diploid
➔ Haploid cells’ nuclei carry one chromosome of each pair
◆ n
◆ all gametes (sex cells) are diploid
◆ gametes fuse to form zygotes
◆ only contain one allele
➔ Alleles: various specific forms of same gene
◆ formed by mutation
◆ alleles differ by only one or a few bases
➔ Genome: whole of the genetic information of an organism
◆ Entire base sequence of human genes was sequenced in Human Genome Project
◆ Genome size: total amount of DNA
➔ Genotype: combination of alleles on chromosome pairs (Rr)
➔ Phenotype: what is expressed (R)
◆ Homozygous dominant (RR)
, ◆ Homozygous recessive (r)
◆ Heterozygous (Rr)
➔ Karyotype: property of a cell, number and type of chromosomes present in nucleus
◆ Karyogram: photograph of chromosomes in homologous pairs + decreasing length;
taken during metaphase of mitosis
➔ Sex chromosomes / heterosomes determine sex // autosomes are chromosomes that do
not determine sex
◆ alleles on men’s sex chromosomes are hemizygous (only on one chromosome)
➔ Prokaryotes have one chromosome with one circular DNA molecule - genophore
◆ some prokaryotes also have plasmids, unlike eukaryotes
● plasmids: additional circular DNA molecules
◆ naked DNA - not associated with protein
➔ Eukaryotic chromosomes are linear DNA molecules associated with histone proteins
◆ there are different chromosomes that carry different genes
➔ Polyploidy vs aneuploidy due to nondisjunction
◆ Gametes with extra or missing chromosomes
◆ Leads to conditions like Down’s syndrome (extra chromosome) or Klinefelter’s
syndrome (XXY sex chromosomes)
Diseases
➔ Many genetic diseases are due to recessive alleles on autosomal genes
➔ sex-linked patterns of inheritance are different
◆ sex-linked diseases are usually on X chromosome since it is longer + has more
genes
◆ only women can be carriers of recessive diseases, as dominant gene will mask it;
men will suffer more from recessive diseases on X chromosome
➔ Radiation + mutagenic chemicals increase mutation rate → can cause genetic diseases or
cancer (carcinogens)
➔ Cystic fibrosis: recessive autosomal trait
➔ Huntington's Chorea: dominant autosomal trait
➔ Sickle cell anemia: co-dominant autosomal trait
caused by base substitution mutation
◆ glutamic acid is replaced by valine as sixth
amino acid in hemoglobin polypeptide
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