Definition

Noun: 1. A genetic cross used to determine an unknown genotype: A test-cross is a specific breeding experiment in genetics. It involves crossing an individual with an unknown genotype for a particular trait with an individual that is homozygous recessive for that same trait. The phenotypes of the resulting offspring are then analyzed to deduce the unknown genotype of the first parent.

Usage and Examples

• Noun:
  • The biologist performed a test-cross to determine if the pea plant with round seeds was homozygous dominant or heterozygous.
  • In a classic Mendelian test-cross, if any offspring display the recessive phenotype, the parent with the unknown genotype must be heterozygous.

Advanced Usage and Concepts

• Purpose in Genetic Analysis: The test-cross is a fundamental tool for revealing whether an organism displaying a dominant phenotype is homozygous (carrying two dominant alleles) or heterozygous (carrying one dominant and one recessive allele). The homozygous recessive parent, often called the "tester," can only contribute a recessive allele, so the offspring's traits directly reflect the alleles contributed by the parent with the unknown genotype.
• Interpreting Results:
  • If all offspring show the dominant phenotype, the unknown parent is likely homozygous dominant.
  • If the offspring show a mix of dominant and recessive phenotypes (approximately a 1:1 ratio), the unknown parent is heterozygous.

Variants and Related Words

• Backcross (n): A broader term for crossing a hybrid with one of its parents or an organism genetically identical to a parent. A test-cross is a specific type of backcross where the parent used is homozygous recessive.
• Tester (n): In genetics, the homozygous recessive individual used in a test-cross.

Synonyms

• Backcross (specifically when the cross is to a homozygous recessive parent)
• Test mating (a more general term used in animal breeding)

Related Phrases and Terms

• "To perform a test-cross": The action of conducting this genetic experiment.
  • The next step in the experiment is to perform a test-cross.
• "Test-cross progeny": Refers to the offspring resulting from a test-cross.
  • The ratio in the test-cross progeny confirmed the hypothesis.

Noun

1. a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring