test cross

(noun)

In genetics, a test cross, first introduced by Gregor Mendel, is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait. Simplier, test crosses determine the genotype of an individual with a dominant phenotype.

Related Terms

Examples of test cross in the following topics:

  • The Punnett Square Approach for a Monohybrid Cross

    • Called the test cross , this technique is still used by plant and animal breeders.
    • In a test cross, the dominant-expressing organism is crossed with an organism that is homozygous recessive for the same characteristic.
    • The test cross further validates Mendel's postulate that pairs of unit factors segregate equally.
    • A test cross can be performed to determine whether an organism expressing a dominant trait is a homozygote or a heterozygote.
    • This cross produces F1 heterozygotes with a yellow phenotype.

  • Typing and Cross-Matching for Transfusions

    • Blood banks test donor blood to ensure recipient compatibility, reducing the risk of hemolytic reaction, renal failure, and death.
    • Due to the different antigen blood types, blood must be cross-matched during processing to avoid potential complications.
    • Much of the routine work of a blood bank involves testing blood from both donors and recipients to ensure that every recipient is given blood that is compatible and is as safe as possible.
    • Several laboratory tests allow cross-matching of compatible blood between donor and recipient.
    • Explain the purposes of typing and of cross-matching blood prior to transfusion

  • Agglutination Reactions

    • Agglutination reactions apply to particulate test antigens that have been conjugated to a carrier.
    • The endpoint of the test is the observation of clumps resulting from that antigen-antibody complex formation.
    • If an antigen is present in a test specimen, it will bind to the antibody and form visible, cross-linked aggregates.
    • Agglutination tests are easy to perform and in some cases are the most sensitive tests currently available.
    • These tests have a wide range of applications in the clinical diagnosis of non-infectious immune disorders and infectious disease.

  • Testes Ducts

    • Testes ducts, which include the seminiferous tubules and vas deferens, are involved in the creation or transportation of sperm.
    • Seminiferous tubules are located in the testes, and is where meiosis occurs and the gametes (spermatozoa) are created.
    • Seminiferous tubule in cross-section (large tubular structure - center of image) with sperm (black, tiny, ovoid bodies furthest from the outer edge of the tubular structure).
    • Diagram of cross-section of testes: 1: Testicular septa 2: Convoluted seminiferous tubules 3: Testicular lobules 4: Straight seminiferous tubules 5: Efferent ductules 6: Rete testis.

  • Diagnostic Blood Tests

    • They are also used in drug tests.
    • Although the term blood test is used, most routine tests (except for most hematology) are done on blood plasma instead of blood cells.
    • For these reasons, blood tests are the most commonly-performed medical tests.
    • While the regular glucose test is taken at a certain point in time, the glucose tolerance test involves repeated testing to determine the rate at which glucose is processed by the body.
    • These tests include: complete blood count, hematocrit (mean corpuscular volume), erythrocyte sedimentation rate (ESR), cross-matching (to determine blood type for transfusion or transplant), and blood cultures (done if infection is suspected).

  • Validity and Reliability of Personality Assessments

    • Because of this, objective tests are said to have more validity than projective tests.
    • In contrast to objective tests, projective tests are much more sensitive to the examiner's beliefs.
    • In the Thematic Apperception Test, however, which involves open-ended storytelling, standardization of test administration is virtually nonexistent, making the test relatively low on validity and reliability.
    • For many decades, traditional projective tests have been used in cross-cultural personality assessments.
    • However, it was found that test bias limited their usefulness.

  • Two-Way ANOVA

    • The two-way analysis of variance (ANOVA) test is an extension of the one-way ANOVA test that examines the influence of different categorical independent variables on one dependent variable.
    • As with other parametric tests, we make the following assumptions when using two-way ANOVA:
    • We define a factorial design as having fully replicated measures on two or more crossed factors.
    • In a factorial design multiple independent effects are tested simultaneously.
    • All terms require hypothesis tests.

  • Structure of a Nerve

    • It prevents certain molecules from crossing from the blood into the endoneurial fluid.
    • The impulses travel from one neuron to another by crossing a synapse, and the message is converted from electrical to chemical and then back to electrical.
    • Neurologists usually diagnose disorders of the nerves by a physical examination, including the testing of reflexes, walking and other directed movements, muscle weakness, proprioception, and the sense of touch.
    • This initial exam can be followed with tests such as nerve conduction study, electromyography, or computed tomography.
    • An illustration of a cross-section of a nerve highlighting the epineurium and perineurium.

  • One-to-One Functions

    • An easy way to check if a function is a one-to-one is by graphing it and then performing the horizontal line test.
    • One way to check if the function is one-to-one is to graph the function and perform the horizontal line test.  
    • The graph below shows that it forms a parabola and fails the horizontal line test.
    • Notice it fails the horizontal line test.
    • Because the horizontal line crosses the graph of the function more than once, it fails the horizontal line test and cannot be one-to-one.

  • Complementation

    • If, when these strains are crossed with each other, some offspring show recovery of the wild-type phenotype, they are said to show "genetic complementation".
    • A complementation test (sometimes called a "cis-trans" test) refers to this experiment, developed by American geneticist Edward B.
    • The beauty of this test is that the trait can serve as a read-out of gene function even without knowledge of what the gene is doing at a molecular level.
    • Example of a complementation test.
    • Flies from Strain 1 have complementary mutations to flies from Strain 2 because when they are crossed the offspring are able to complete the full metabolic pathway and thus have red eyes.