Genetic Definitions - Some Definitions for Genetics...

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Unformatted text preview: Some Definitions for Genetics Genetics GENE GENE A heredity factor for a particular character (e.g., seed shape in peas); Mendel hypothesized that each organism had two genes for the character. One of these genes was derived maternally and the other derived paternally. Allele Allele One of several possible states for a gene. Mendel hypothesized that there were two possible alleles (e.g., round seeds versus wrinkled seeds) for each character (e.g., seed shape). Biology 100 Biology Human Biology Genotype The genetic make up of an organism; the actual alleles that are present. Homozygous Homozygous When the genotype for a particular character consists of two identical alleles (e.g., RR or rr). Heterozygous Heterozygous When the genotype for a particular character consists of two different alleles (e.g., Rr). Biology 100 Human Biology Phenotype The actual appearance of the organism. The phenotype is a result of the expression of the genotype as the physical characteristics of the organism. The phenotype may also involve the interaction of the organism with its environment. environment. Biology 100 Human Biology Dominant Dominant Allele Allele Of the two possible alleles involved in determining the genotype of an organism, one of these alleles is said to be dominant if it masks the expression of the other allele in the heterozygote (e.g., round is dominant over wrinkled). dominant Biology 100 Biology Human Biology Recessiv e Allele An allele is said to be recessive if its expression is masked by the presence of the other allele in the heterozygote. Recessive traits may be observed as the phenotype when the genotype is homozygous for the recessive allele (e.g., rr). Biology 100 Human Biology Genotype Versus Genotype Genotype Genotype Phenotype Phenotype Phenotype RR rr Seeds Seeds Rr Round Seeds Wrinkled Wrinkled Round Seeds Biology 100 Biology Human Biology TrueBreeding When a group of organisms “breed true” for a particular trait, their offspring and their offsprings’ descendants always exhibit that trait. In order to be true-breed for a trait, the organism must be homozygous (e.g., either RR or rr) for the trait in question. Biology 100 Human Biology Hybrid The offspring resulting from crossing two different truecrossing breeding parents (e.g., the breeding offspring resulting when crossing RR with rr). In which case, the offspring will be heterozygous (e.g., Rr) (e.g., Biology 100 Biology Human Biology Recessiv e Allele An allele is said to be recessive if its expression is masked by the presence of the other allele in the heterozygote. Recessive traits may be observed as the phenotype when the genotype is homozygous for the recessive allele (e.g., rr). ...
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This note was uploaded on 04/19/2011 for the course BIOL 101 taught by Professor Wong during the Fall '09 term at University of Hawaii, Manoa.

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