GENETICS TERMINOLOGY
1 . THE BASICS: DNA AND GENES
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Genetics: The study of heredity and the variations of these
inherited characteristics.
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Gene: A specific segment of DNA that codes for a particular
protein, which in turn determines a characteristic (like eye colour).
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Controls structural and physiological characteristics
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Chromatin: The thread-like formation of DNA found in the nucleus
when a cell isn't dividing.
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Chromosome: DNA that has coiled up tightly into a visible
structure during cell division.
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Homologous chromosomes: A pair of identically shaped and
structured chromosomes, one from the mother and the other from
the father.
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Genome: Complete set of all the genes in all the chromosomes of
a particular species.
2. THE MECHANICS OF INHERITANCE
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Monogenic inheritance: The inheritance of characteristics that are controlled by only one gene at a
single locus on the chromosome. For example, freckles and earlobe attachment.
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Polygenic inheritance: The inheritance of characteristics that are controlled by more than one gene at
more than one loci on one or more chromosomes. For example, skin colour and height.
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Allele: Different versions of the same gene. For example, if the gene is "Height," the alleles might be
"Tall" and "Short."
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Locus: The specific location or position of a gene on a chromosome.
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Dominant Allele: An allele that masks the expression of a recessive allele. It’s always expressed in the
phenotype if present (represented by a capital letter, e.g., T).
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Recessive Allele: An allele that is only expressed if two copies are present (represented by a
lowercase letter, e.g., t).
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Genotype: The genetic makeup of an organism (the letters, like Tt).
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Phenotype: The physical appearance or visible trait of the organism (like "Tall").
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Genotype determines phenotype
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Homozygous: Having two identical alleles for a trait (e.g., TT or tt). Also called "pure breeding."
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Heterozygous: Having two different alleles for a trait (e.g., Tt). Also called a "hybrid."
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Created by Mrs Nadel-Nel
3. GENETIC CROSSES
The tools we use to predict what the "kids" will look like.
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Monohybrid Cross: A genetic cross involving only one characteristic (e.g., seed colour).
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Punnett Square: A grid used to calculate the probability of genotypes and phenotypes in offspring.
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Genotypic Ratio: Writing the genotype out as a ratio (e.g., 1 TT : 2 Tt : 1 tt).
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Phenotypic Ratio: Writing the phenotype out as a ratio (e.g., 3 Tall : 1 Short).
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Created by Mrs Nadel-Nel