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Units of information on heritable traits, which parents transmit to offspring.
Each gene has its own locus, or location, along the length of a particular chromosome. |
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| Cells with a diploid chromosome number (2n) have pairs of genes, on pairs of homologous chromosomes. |
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| Alters a gene's molecular structure and its message about a trait. It may cause a trait to change, as when a gene for flower color specifies yellow and a mutant form of the gene specifies white. |
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| All molecular forms of the same gene. |
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Offspring of a cross between two individuals that breed true for different forms of a trait.
Each inherited nonidentical alleles for a trait being studied. |
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| Has a pair of dominant alleles (AA) for the trait under study. |
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| Has a pair of recessive alleles (aa). |
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| Has a pair of nonidentical alleles (Aa) |
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| Two homozygous parents differ in a trait that is governed by alleles of one gene. They are crossed to produce F1 offspring that are all heterozygous. |
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| The change that each outcome of an event will occur is proportional to the number of ways in which the outcome can be reached. |
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| A simple way to predict that probably outcomes of a genetic cross by constructing and filling in a diagram of all possible combinations of genotypes, phenotypes, or both. |
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| A cross that might reveal the (unknown) genotype of an individual showing dominance for a trait; the individual is crossed with a known homozygous recessive individual. |
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Mendel: Diploid cells have pairs of genes on pairs of homologous chromosomes. The two genes of each pair are separated from each other during meiosis,so they end up in different gametes.
Every organism carries pairs of factors, called alleles, for each trait and the members of the pair segregate (separate) during the formation of gametes. For example, if an individual is Bb for eye color, during gamete formation, one gamete would receive a B, and the other made from that cell would receive a b. |
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| Start with a cross between true breeding homozygous parents that differ in two traits governed by alleles of two genes. The F1 offspring are all heterozygous for the alleles of both genes. |
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An outcome of random alignments at metaphase 1 of meiosis. Each homologous chromosome and its partner -- and the genes they carry -- are assorted into different gametes independently of the other pairs. Crossing over can affect the outcome.
Members of each pair of factors are distributed independently when the gametes are formed. Quite simply, inheritance of one trait or characteristic does not interfere with inheritance of another trait. For example, if an individual is BbRr for two genes, gametes formed during meiosis could contain BR, Br, bR, or br. The B and b alleles assort independently of the R and r alleles. |
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| Three or more slightly different molecular forms of a gene that persists among the individuals of a population. |
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A case of alleles at a single gene locus having positive or negative impact on two or more traits.
Example: Mutation that causes sickle ell anemia. This single gene mutation "sickles" the blood cells, leading to systemic symptoms such as heart, lung, and kidney damage; muscle pain; weakness; and generalized fatigue. |
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| All genes on a chromosome. |
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| Of individuals of a population, a range of small differences in the phenotypic expression of a trait. |
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Inheritance of multiple genes that affect the same trait.
Eye color is an example of a polygenic trait. The tone (color), amount (blue eyes have less than brown eyes), and position (how evenly distributed the pigment is) of pigment all play a role in determining eye color.
Skin color. |
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An interaction among products of two or more gene pairs that influence the same trait.
Example: Coat color of mice. |
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| The first to gather evidence of patterns by which genes are transmitted rom parents to offspring. |
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| The first generation of offspring, or the first "filial" generation in a genetic cross. |
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| The second generation of offspring, or the second "filial" generation in a genetic cross. |
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| An organism's genetic makeup for a given trait. A simple example of this could involve eye color where B represents the allele for brown and b represents the allele for blue. The possible genotypes include homozygous brown (BB), heterozygous brown (Bb), and homozygous blue (bb). |
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| The physical expression of the trait associated with a particular genotype. Some examples of the phenotypes for Mendel's peas were round or wrinkled, green or yellow, purple or white flower. |
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| Mendel: This states that when two opposite pure-breeding varieties of an organism are crossed, all the offspring resemble one parent. This is referred to as the dominant trait. The variety that is hidden is referred to as the recessive trait. |
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An individual heterozygous for a trait (Yy) shows characteristics not exactly like any parent. The phenotype is a "mixture" of both of the parents' genetic input.
There are two major types of intermediate inheritance:
1. Incomplete dominance or "blending inheritance"
2. Codominance |
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| The heterozygous genotype produces an "intermediate" phenotype rather than the dominant phenotype; neither allele dominates the other. A classic example is flower color in snapdragons-- crossing a snapdragon plant that has red flowers with one that has white flowers yields offspring with pink flowers. |
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Situation in which both alleles express themselves fully in a heterozygous organism.
Human blood groups. Both alleles are fully expressed in the phenotype. |
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| A form of genetic recombination that occurs during prophase 1 of meiosis, led to their production. The less often this recombination occurs, the closer the genes must be on the chromosome. THe farther apart two genes are on a chromosome, the more often crossover will occur. Recombination frequency can be used to determine how close two genes are on a chromosome through the creation of linkage maps. |
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| Genetic map put together using crossover frequencies. |
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| Used to geographically relate the genes on the basis of these frequencies. |
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