Biology 4.3 - Inheritance DEFINITIONS

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Gene
A sequence of DNA that codes for a particular polypeptide with a specific locus on a chromosome.
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Locus
The specific position of a gene or mutation on a chromosome.
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Allele
A variant nucleotide sequence for a gene at a given locus that codes for an altered phenotype.
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Dominant
An allele is described as 'dominant' when it is always expressed when present.
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Recessive
An allele is described as 'recessive' when it is not expressed in the presence of a dominant allele. It is only expressed when the alleles are homozygous.
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Phenotype
The characteristic/appearance of a gene.
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Genotype
The set of alleles that determines the expression of a characteristic/trait.
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Homozygous.
If the alleles for a particular gene are the same, e.g. RR, tt.
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Heterozygous
If the alleles for a particular gene are different, e.g. Rr, Tt
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Autosomes
Any chromosome that is not a sex chromosome is an autosome.
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Sex chromosome
A chromosome involved in the determination of the sex of an organism.
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Monohybrid inheritance
Inheritance controlled by a single gene.
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Law of segregation (first law)
This law states that the characteristics of an organism are determined by alleles which occur in pairs. In gametes, only one of the pair is present.
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Dihybrid inheritance
The simultaneous inheritance of two unlinked genes (e.g. genes on different chromosomes).
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Karyotype
The arrangement of homologous pairs in decreasing size order.
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Sex linkage
When a gene is carried by a sex chromosome, and as a result the characteristic it encodes is seen predominantly in one sex.
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Sex-linked recessive allele
A gene that is carried by a sex chromosome that must be present in both chromosomes to be expressed in females, but is always expressed in males.
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Duchenne Muscular Dystrophy (DMD)
An X-linked recessive condition that causes the gradual loss of muscle mass and progressive muscle weakness.
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Mutation
A random, spontaneous event that changes the amount, arrangement or structure of DNA.
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Mutagen
An agent that changes the amount, arrangement or structure of DNA.
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Carcinogen
An agent that causes cancer.
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Oncogene
A proto-oncogene with a mutation that results in cancer.
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Card 2

Front

Locus

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The specific position of a gene or mutation on a chromosome.

Card 3

Front

Allele

Back

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Card 4

Front

Dominant

Back

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Card 5

Front

Recessive

Back

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