Term
|
Definition
| the most prevalent allele in a population that encodes a functionally active protein. |
|
|
Term
| Mutant/Recessive or loss of function allele |
|
Definition
| altered by mutation. recessive alleles cause a substantial decrease in the expression of a functional protein, but does not affect the phenotype of the heterozygote because 50% of the functional protein encoded by the normal gene is adequate to provide a normal phenotype. More likely to eliminate a trait. |
|
|
Term
| Essential gene/Lethal allele/Nonessential gene/Conditional lethal alleles |
|
Definition
| necessary for survival/ causes the death of an organism/ not required for survival but beneficial/ cause lethality under a given set of circumstances such as temperature |
|
|
Term
|
Definition
| the heterozygote exhibits a phenotype that is intermediate between the corresponding homozygous individuals. get 1:2:1 instead of expected 3:1. at cellular or molecular level, it is more likely alleles will be incompletely dominant. 50% of the normal protein cannot accomplish the same level of pigment synthesis that 100% of the protein can. |
|
|
Term
| Multiple alleles of that gene |
|
Definition
| when a single gene exists in 2 or more alleles such as coat color in rabbits |
|
|
Term
|
Definition
| the Ia and Ib alleles of ABO blood group are codominant to each other but are dominant to the i allele. Tyoes O and AB provide an unambiguous genotype because O can only be ii and AB can only be IAIB. |
|
|
Term
|
Definition
| analogous to incomplete dominance; 2 copies of the allele (in females) provides more color than 1 copy of the allele (in males). for ex. the eosin allele |
|
|
Term
| Overdominance or heterozygote advantage |
|
Definition
| heterozygotes may display characteristics that are more beneficial to their survival and reproduction than either corresponding homozygote. Heterozygotes for sickle cell anemia have resistance to malaria and do not suffer from the disease. 3 mechanisms for overdominance: 1)Disease resistance 2)Homodimer formation 3) Variation in functional activity |
|
|
Term
|
Definition
| when dominant alleles are not phenotypically expressed such as polydactyly. The degree of expression is the expressivity of a trait. |
|
|
Term
| Sex-influenced inheritance |
|
Definition
| alleles that are dominant in one gender but recessive in the opposite gender such as human pattern baldness |
|
|
Term
|
Definition
| traits found only in one of the two genders such as feather type in chickens |
|
|
Term
| Cross between 2 gene that exist in both dominant and recessive alleles with four phenotypes produced |
|
Definition
| a cross between 2 individuals that are heterozygous for both genes produces a 9:3:3:1 ratio. |
|
|
Term
| Cross between 2 genes existing in both dominant and recessive alleles when the recessive alleles are EPISTATIC to the dominant alleles of the other gene. |
|
Definition
| produces a 9:7 ratio in offspring in a cross between 2 heterozygous individuals. Epistatic interactions are explained by different proteins participating in an enzymatic pathway leading to the formation of a single product. |
|
|
Term
| Cream allele and epistasis |
|
Definition
| autosomal recessive and not in the same gene as the eosin allele which is X-linked. Epistasis refers to the situation where one gene masks the phenotypic effects of a different gene. In flies, the cream-colored eyes are due to the effect of a second gene that modifies the expression of the eosin allele. |
|
|
Term
|
Definition
| two or more genes can be located on the same chromosome and are physically linked to each other because each eukaryotic chromosome contains a single,continuous,linear piece of DNA. |
|
|
Term
|
Definition
| During the prophase of meiosis I, homologous chromosomes pair and form synapses. The paired chromosomes are called bivalents. The bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent. |
|
|
Term
| Genetic recombination/nonparental/parental |
|
Definition
| crossover resulting in gametes in which the arrangement of linked alleles has been changed. the gametes are nonparental or recombinant gametes and their offspring will have different traits than either parent. Offspring with same combination of alleles as parents are parental or nonrecombinant offspring. |
|
|
Term
| Bateson and Punnett discovered that 2 traits that did not assort independently |
|
Definition
| they suggested that the transmission of these traits from the parental to F2 generation was coupled. They did not realize that the coupling was due to the linkage of the two genes on the same chromosome. |
|
|
Term
| Morgan provided evidence for linkage of genes |
|
Definition
| He proposed that linkage is due to the occurrence of 2 or more different genes on the same chromosome. He studied 3 X-linked traits and proposed that all 3 genes are located on the same X chromosome. He proposed to explain occurrence of nonparentals and difference in certain combinations: 1.Homologous X chromosomes in the female can exchange pieces of chromosomes and create new nonparental combinations of alleles. 2.The likelihood of crossing over depends on the distance between 2 genes. |
|
|
Term
| Chi-square analysis to determine linkage vs. independent assortment |
|
Definition
| 1.Hypothesize that genes are not linked(independent assortment hypothesis)This allows calculation of expected # of offspring based on genotypes of the parents and the law of independent assortment 2.Calculate expected values of each of the 4 phenotypes based on hypothesis 3.Calculate and interpret. If the deviations between the observed and expected values are too large to occur as a matter of chance and reject hypothesis. |
|
|
Term
| Data of Creighton and McClintock correlated crossing over with formation of nonparental offspring involving linked genes |
|
Definition
| Crossover between C and wx genes. They followed transmission of chromosomes that had morphologically distinguishing features.The abnormal chromosome(Cwx) demonstrated that 2 homologous chromosomes physically exchanged segments as a result of crossing over. Normal chromosome 9 and a knobbed/translocated chromosome 9 crossover produced a chromosome that had either a knob or a translocation but not both. They hypothesized that offspring with nonparental phenotypes were the product of a crossover via the exchange of chromosomal segments btwn homologous chromosomes. |
|
|
Term
|
Definition
| less frequent crossing over during an early stage of embryonic development causing a patch of tissue in the adult that is genetically and phenotypically different from the rest of the organism. "Twin Spots" |
|
|
Term
|
Definition
| the use of crosses as a method to determine the linear order of genes that are linked to each other along the same chromosome. |
|
|
Term
| Map distance along a chromosome and frequency of recombination between 2 genes |
|
Definition
| the percentage of recombinant offspring is a measure of the distance between 2 genes!(Morgan's experiment) |
|
|
Term
| Test Cross to determine if recombination has occurred during gamete formation(meiosis) in the heterozygous parent |
|
Definition
| Used to determine the # of offspring that can only be explained by crossing over. Cross an individual heterozygous for 2 or more genes and an individual recessive and homozygous for these same genes. |
|
|
Term
| Sturtevant used the frequency of crossing over btwn 2 genes to produce the first genetic map. |
|
Definition
| As the percentage of recombinant offspring approaches a value of 50%, this value becomes progressively more inaccurate as a measure of map distance. When the distance btwn 2 genes is relatively large, the likelihood of multiple crossovers in this region causes the observed # of recombinant offspring to be an underestimate of the true distance btwn the 2 genes. |
|
|
Term
| Trihybrid crosses used to determine the order of and distance btwn 3 linked genes. |
|
Definition
| 1.Cross 2 true-breeding strains that differ with regard to 3 alleles to obtain F1 individuals heterozygous for all 3 alleles with all dominant and recessive alleles located on separate homologous chromosomes. 2.Mate F1 female heterozygotes to male flies homozygous recessive for all 3 alleles and crossovers during gametogenesis in females may produce new combos 3.Collect data for F2 generation with 8 possible combos of offspring. The combo of the traits in the double crossover indicates which genes is in the middle. 4.Calculate map distance btwn pairs of genes by regrouping data according to pairs of genes or calculate % of single and double crossovers. 5.Construct the map by using distance btwn genes that are closest together. |
|
|
Term
|
Definition
| When a crossover occurs in one region of a chromosome, it often decreases the probability that another crossover will occur nearby. |
|
|
