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Trihybrid Crosses

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal...

Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.

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Formation of Species

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Incomplete Dominance

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Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.

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Massive haplotypes underlie ecotypic differentiation in sunflowers.

Marco Todesco^1,2, Gregory L Owens^1,2,3, Natalia Bercovich^4,5

¹Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada.

|July 10, 2020

Summary

Large, non-recombining haplotype blocks maintain adaptive alleles in wild sunflowers, driving ecotype differentiation. Structural variation plays a key role in this ecotypic adaptation process.

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Area of Science:

Evolutionary biology
Genetics
Ecology

Background:

Species often comprise ecotypes adapted to diverse environments.
Mechanisms of ecotype formation and maintenance, especially under hybridization, remain poorly understood.

Purpose of the Study:

Investigate the genetic basis of ecotypic differentiation in wild sunflowers.
Identify genomic regions and mechanisms responsible for maintaining adaptive traits across different environments.

Main Methods:

Resequencing of 1,506 wild sunflowers across three species (Helianthus annuus, H. petiolaris, H. argophyllus).
Identification and analysis of large, non-recombining haplotype blocks.
Association analysis of haplotype blocks with ecological traits and environmental factors.

Main Results:

Discovered 37 large (1-100 Mbp) non-recombining haplotype blocks associated with ecological traits and environmental conditions.
These blocks maintain adaptive alleles, differentiating sunflower ecotypes and showing significant effects on traits like flowering time and seed size.
Haplotype blocks are highly divergent, linked to structural variants, and may represent introgressions from related species.

Conclusions:

Limited recombination within specific haplotype blocks is crucial for maintaining adaptive allele combinations and driving ecotype divergence.
Structural variation significantly contributes to ecotypic adaptation in wild sunflowers.