A concise, bullet-pointed summary on Genetics. Covers strictly what you need to know for all tests and assessments (as dictated by the SAGS guidelines). Includes annotated diagrams and images to illustrate points mentioned, as well as additional research, helpful when understanding the work
Gregor Mendel, the father of genetics
• Gregor Mendel started a series of experiments on garden peas that would reveal several
fundamental principles of genetics
• Over a 10 year period he studied inheritance in pea plants
• Mendel used pea plants to study how a particular characteristic was passed down from
one generation to the next
• The pea plants that he used had opposing characteristics eg. Long stem vs short stem
• First he test planted them for 2 years and self pollinated them by hand to make sure
that they were homozygous (pure-breeding), hence their offspring were identical for
many generations
• The first set of plants that is crossed in an experiment is called the parental generation
(P) and their offspring is called the first filial generation (F1)
• F1 generation can be self or cross pollinated and their offspring is called the second
filial generation (F2)
• Mendel found that the inheritance of characteristics is determined by genes
• He also found that genes for a particular characteristic occurred in pairs and within the
pair, the genes may be the same or different
• If the genes were different then the action of the one of the two was dominant and the
other recessive
Genetics: the study of the behaviour of genes
Genes: the hereditary factors contained on the DNA, pairs of genes on each homologous
chromosome / sections of DNA that code for a characteristic
Characteristics/traits: how the gene is expressed eg. The gene of eye colour gives you
blue or brown eyes
Locus: the position on the chromosome where a certain gene is found
Allele: the name given to genes which copy corresponding loci on a homologous pair of
chromosomes, only two alleles for each gene
Monohybrid cross: a genetic cross between parents for only one gene
Homozygous: the 2 alleles on corresponding loci are the same
Heterozygous: the 2 alleles on corresponding loci are different
Dominant: the gene in a heterozygous pair shows its characteristics
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, Genotype: the genetic makeup present in an organism
Phenotype: describes the visible physical appearance
Family Trees / Pedigree charts
• A pedigree diagram is a construction of a set of symbols that allows for us to record a
particular phenotypic trait in many generations of a family
• Helps to see whether a couple is likely to pass on a genetic disease
• Reveals several generations of individuals in a family
• How to read a pedigree chart
• Number every generation from top to bottom in roman numerals
• Number each individual starting with the top left and moving right and down
• Males are represented by squares and females by circles
• Darkened shapes represent affected individuals
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