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| Gregor Johann Mendel was an Austrian priest and scientist, and is often called the father of genetics for his study of the inheritance of traits in pea plants. Mendel showed that the inheritance of traits follows particular laws, which were later named after him. |
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| If two alleles differ, then one, the dominant, will be fully expressed while the other, the recessive, will not be expressed. |
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| Mendel's first law, stating that allele pairs separate during gamete formation, and then randomly re-form as pairs during the fusion of gametes at fertilization. |
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| A Monohybrid cross is a cross between parents who are heterozygous at one locus; for example, Bb x Bb. |
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| Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar in order to achieve offspring with a genetic identity closer to that of the parent. A testcross is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait. Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. If all offspring display the dominant phenotype, the individual in question is homozygous dominant; if the offspring display both dominant and recessive phenotypes, then the individual is heterozygous. |
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| Law of Independent Assortment |
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| The Law of Independent Assortment, also known as "Inheritance Law", states that the inheritance pattern of one trait will not affect the inheritance pattern of another. While Mendel's experiments with mixing one trait always resulted in a 3:1 ratio between dominant and recessive phenotypes, his experiments with mixing two traits (dihybrid cross) showed 9:3:3:1 ratios. Independent assortment occurs during meiosis I in eukaryotic organisms, specifically anaphase I of meiosis, to produce a gamete with a mixture of the organism's maternal and paternal chromosomes. Along with chromosomal crossover, this process aids in increasing genetic diversity by producing novel genetic combinations. |
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| A heterozygous genotype that creates an intermediate phenotype. In this case, only one allele (usually the wild type) at the single locus is expressed in a doseage dependent manner, which results in an intermediate phenotype. Ex. RR x rr= Rr |
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| Neither phenotype is recessive. Instead, the heterozygous individual expresses both phenotypes. Ex A x B=AB |
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| Most genes exist in populations in more than two allelic forms. Ex. Blood groups, AB. |
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| Epistasis is the interaction between genes. Epistasis takes place when the action of one gene is modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is said to be epistatic, while the phenotype altered or suppressed is said to be hypostatic. |
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| Occurs when a single gene influences multiple phenotypic traits. Consequently, a new mutation in the gene will have an effect on all traits simultaneously. |
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| The inheritance of a phenotypic characteristic that varies in degree and can be attributed to the interactions between two or more genes and their environment. |
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| Refers to variations of a phenotype in individuals carrying a particular genotype. |
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| Genes and the Environment |
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| Occurs when particular genetic loci or alleles for genes are inherited jointly. Genetic loci on the same chromosome are physically connected and tend to segregate together during meiosis, and are thus genetically linked. Alleles for genes on different chromosomes are usually not linked, due to independent assortment of chromosomes during meiosis. |
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| A genetic map of a species or experimental population that shows the position of its known genes and/or genetic markers relative to each other in terms of recombination frequency, rather than as specific physical distance along each chromosome. A genetic map is a map based on the frequencies of recombination between markers during crossover of homologous chromosomes. The greater the frequency of recombination (segregation) between two genetic markers, the farther apart they are assumed to be. |
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| Sex linkage is the phenotypic expression of an allele that is related to the chromosomal sex of the individual. Genes that are present on the X or Y chromosome are called sex linked genes. |
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| The interrelationships of parents and children across the generations. |
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| A Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male. The inactivation state of chromosomes is passed on to daughter cells during mitosis. |
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| changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division. |
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| Results of Gene Mutations (A) |
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| Results of Gene Mutations (B) |
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| Deletion: Removes a chromosomal segment. Duplication: Repeats a segment. Inversion: Reverses a segment. Translocation: Switches segments between chromosomes. |
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| The characteristic chromosome complement of a eukaryote species. The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes. |
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| The failure of chromosome pairs to separate properly during cell division. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes. When a single chromosome is lost (2n-1), it is called a monosomy, in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs. When a chromosome is gained, it is called trisomy, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs. |
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| A non-sex chromosome. It is an ordinarily paired[1] type of chromosome that is the same in both sexes of a species. For example, in humans, there are 22 pairs of autosomes. |
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| A genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner. It is an inheritance process independent of the classical Mendelian inheritance. Imprinted genes are either expressed only from the allele inherited from the mother, or in other instances from the allele inherited from the father. |
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| Results in a spectrum of characteristic physical, intellectual, emotional and behavioural features which range from severe to mild in manifestation. The syndrome is associated with the expansion (excessive repetition) of a single trinucleotide gene sequence (CGG) on the X chromosome, and results in a failure to express the FMR-1 protein which is required for normal neural development. |
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| The transmission of genes that occur outside the nucleus. |
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