Test cross

<p>Under the <a href="/facts/Mendelian_inheritance/v2038wkl">law of dominance</a> in <a href="/facts/Genetics/bu8wne0A">genetics</a>, an individual expressing a <a href="/facts/Dominance_(genetics)/DsvtPyQU">dominant</a> <a href="/facts/Phenotype/vxWXKGLj">phenotype</a> could contain either two copies of the dominant <a href="/facts/Allele/8FxCS9KA">allele</a> (<a href="/facts/Homozygous/XzEJ5gPp">homozygous</a> dominant) or one copy of each dominant and <a href="/facts/Dominance_(genetics)/DsvtPyQU">recessive</a> allele (<a href="/facts/Zygosity/XzEJ5gPp">heterozygous</a> dominant). By performing a test cross, one can determine whether the individual is heterozygous or homozygous dominant.
</p><p>In a test cross, the individual in question is bred with another individual that is homozygous for the recessive trait and the <a href="/facts/Offspring/v7LD4qBl">offspring</a> of the test cross are examined. Since the homozygous recessive individual can only pass on recessive alleles, the allele the individual in question passes on determines the phenotype of the offspring. Thus, this test yields 2 possible situations:
</p>
<ol><li>If any of the offspring produced express the recessive trait, the individual in question is heterozygous for the dominant allele.</li>
<li>If all of the offspring produced express the dominant trait, the individual in question is homozygous for the dominant allele.</li></ol>

Test cross open-in-new

Test cross