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Heterosis, hybrid vigor, or outbreeding enhancement is the improved or increased function of any biological quality in a hybrid offspring. An offspring is heterotic if its traits are enhanced as a result of mixing the genetic contributions of its parents.
Hybrid fitness may also differ with cross direction, [25] between first generation and later generation hybrids, [26] and among individuals within generations of the same cross-type. [ 27 ] [ 28 ] In some cases hybrids may evolve into new hybrid species with reproductive isolation to both parent taxa.
When conducting a dihybrid test cross, two dominant phenotypic characteristics are selected and crossed with parents displaying double recessive traits. The phenotypic characteristics of the F1 generation are then analyzed. In such a test cross, if the individual being tested is heterozygous, a phenotypic ratio of 1:1:1:1 is typically observed. [7]
In the example pictured to the right, RRYY/rryy parents result in F 1 offspring that are heterozygous for both R and Y (RrYy). [4] This is a dihybrid cross of two heterozygous parents. The traits observed in this cross are the same traits that Mendel was observing for his experiments. This cross results in the expected phenotypic ratio of 9:3:3:1.
A hybrid between two inbred strains can be used to cancel out deleterious recessive genes resulting in an increase in the mentioned areas. This is known as heterosis. [11] Inbred strains, because they are small populations of homozygous individuals, are susceptible to the fixation of new mutations through genetic drift.
The plants of the F1 generation resulting from this hybrid cross were all heterozygous round and yellow seeds. Classical genetics is a hallmark of the start of great discovery in biology, and has led to increased understanding of multiple important components of molecular genetics, human genetics, medical genetics, and much more.
The masking effect of outcrossing is known as genetic complementation, [3] an effect also recognized as hybrid vigor or heterosis. Once outcrossing is established in a lineage of flowering plants due to the benefit of genetic complementation, subsequent switching to inbreeding becomes disadvantageous because it allows expression of the ...
The words homozygous, heterozygous, and hemizygous are used to describe the genotype of a diploid organism at a single locus on the DNA. Homozygous describes a genotype consisting of two identical alleles at a given locus, heterozygous describes a genotype consisting of two different alleles at a locus, hemizygous describes a genotype consisting of only a single copy of a particular gene in an ...