CHAPTER FIVE
GENETICS AND INHERITANCE
DEFINITIONS
HEREDITY: Transmission of characteristics from parent to offspring.
INHERITANCE:set of characteristics passed from parent to offspring
GENETICS: study of heredity and variations that occur in the transmission of
hereditary characteristics
HOMOLOGOUS PAIR: identical in shape and size. One is maternal and the other
paternal.
AUTOSOMES:contains two sets of diploid chromosomes. One set maternal, the
other paternal.
GONOSOMES:contains one set of haploid chromosomes. Formed by meiosis.
GENES:a particular length of DNA at a particular location on the chromosome
that influences a certain characteristic
DNA: genetic material which makes up a chromosome
LOCUS: particular position of a gene on a chromosome
MONOGENIC INHERITANCE: characteristics controlled by a single gene at a single
locus
POLYGENIC INHERITANCE:characteristics controlled by more than one gene at
different loci on one or more chromosomes
PHENOTYPE: external appearance of an organism
GENOTYPE: genetic composition of an individual. Determines phenotype.
Combination of alleles for a characteristic
ALLELES:alternative forms of a gene found at the same locus and providing
different expressions of a characteristic
DOMINANT:one allele overpowers the other. It determines the phenotype.
, RECESSIVE: One allele is overpowered by the other. Only determines the
phenotype if both alleles are recessive.
HOMOZYGOUS: an individual has two copies of the same allele for a particular
genotype
HETEROZYGOUS: an individual has two different alleles for a particular
genotype
VARIATION: differences between individuals within a population
MUTATION: change in nucleotide sequence of a gene, resulting in a new allele
CROSSING OVER:process of homologous chromosomes exchanging corresponding parts
and thus genes during the first division of meiosis
HYBRID:an offspring from a cross between parents differing in one trait only
INBRED:in plants it is self pollination. In animals it is mating amongst the
offspring of the same parents
MONOHYBRID CROSS:cross between parents differing in one trait only
TRAIT: a gene characteristic
DIHYBRID CROSS:cross between parents differing in two traits
MONOHYBRID CROSSES
GREGOR MENDEL
- an Austrian monk
- did breeding experiments with garden peas from 1857 to 1864 to find out if
contrasting characteristics was a result of the effect of cross fertilisation.
He had 3 laws:
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
GENETICS AND INHERITANCE
DEFINITIONS
HEREDITY: Transmission of characteristics from parent to offspring.
INHERITANCE:set of characteristics passed from parent to offspring
GENETICS: study of heredity and variations that occur in the transmission of
hereditary characteristics
HOMOLOGOUS PAIR: identical in shape and size. One is maternal and the other
paternal.
AUTOSOMES:contains two sets of diploid chromosomes. One set maternal, the
other paternal.
GONOSOMES:contains one set of haploid chromosomes. Formed by meiosis.
GENES:a particular length of DNA at a particular location on the chromosome
that influences a certain characteristic
DNA: genetic material which makes up a chromosome
LOCUS: particular position of a gene on a chromosome
MONOGENIC INHERITANCE: characteristics controlled by a single gene at a single
locus
POLYGENIC INHERITANCE:characteristics controlled by more than one gene at
different loci on one or more chromosomes
PHENOTYPE: external appearance of an organism
GENOTYPE: genetic composition of an individual. Determines phenotype.
Combination of alleles for a characteristic
ALLELES:alternative forms of a gene found at the same locus and providing
different expressions of a characteristic
DOMINANT:one allele overpowers the other. It determines the phenotype.
, RECESSIVE: One allele is overpowered by the other. Only determines the
phenotype if both alleles are recessive.
HOMOZYGOUS: an individual has two copies of the same allele for a particular
genotype
HETEROZYGOUS: an individual has two different alleles for a particular
genotype
VARIATION: differences between individuals within a population
MUTATION: change in nucleotide sequence of a gene, resulting in a new allele
CROSSING OVER:process of homologous chromosomes exchanging corresponding parts
and thus genes during the first division of meiosis
HYBRID:an offspring from a cross between parents differing in one trait only
INBRED:in plants it is self pollination. In animals it is mating amongst the
offspring of the same parents
MONOHYBRID CROSS:cross between parents differing in one trait only
TRAIT: a gene characteristic
DIHYBRID CROSS:cross between parents differing in two traits
MONOHYBRID CROSSES
GREGOR MENDEL
- an Austrian monk
- did breeding experiments with garden peas from 1857 to 1864 to find out if
contrasting characteristics was a result of the effect of cross fertilisation.
He had 3 laws:
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
