A short section of DNA that codes for particular polypeptide
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Allele
A particular form of a gene
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Homozygous
Both alleles of a gene are the same
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Heterogeneous
The alleles of the same gene are different
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Gene locus
The position of the gene on the chromosome
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Dominant
The dominant allele is expressed in the phenotype over the recessive gene (in a heterogeneous condition)
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Phenotype
Outward appearance in terms of trait being considered
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Genotype
The two alleles for a particular trait
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Mendel's first law of inheritance/The law of segregation
The two alleles of each gene separate during meiosis with only one entering each gamete.
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Monohybrid inheritance
The inheritance of alleles at one gene locus
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Co-dominance
The two alleles at a particular gene locus are different but neither has a dominant effect nor masking effect on the other. The phenotype of a heterozygous individual is different to the phenotype of both homogeneous genotypes.
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Multiple alleles
For some traits there is more than two possible alleles for a particular gene in a population at the gene locus. So, the inheritance of the trait is multiple alleic.
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Lethal alleic combinations
Usually lethal alleic combinations result in the spontaneous abortions of embryos or fetuses at a very early stage and are most often recessive so are only expressed when both alleles are present
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Autosomal recessive
Trait appears in only some generations. Approximately even number of males and females are affected
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Autosomal dominant
Impossible to pass on the condition without at least one parent having the trait. Approximately even number of male and female affected.
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X-Linked recessive
More common in males but not present in all males
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X-linked dominant
Not restricted to males the way X-linked recessive traits are
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Dihybrid inheritance
The inheritance of alleles at two gene loci
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Mendel's second law/The Law of independent assortmant
During the formation of gametes, the segregation of the alleles of one gene is independent to the segregation of the alleles of any other gene.
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The aditive effect of the alleles across two gene loci
Some traits are a consequence of the cummulative effect of certain alleles in 2/+ genes. The phenotype is thus dependant on a genotype straddling across two genes
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Epistatsis
A form of gene interaction where one gene interferes with the expression of another gene, or influences it.
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Epigenetics
The role of the environment in affecting a gene expression
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