Genetics
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
1 of 13
, 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
2 of 13
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
1 of 13
, 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
2 of 13
