Hybrid vigour inbreeding project?

Question

One of my friends has to make a project on "hybrid vigour inbreeding".... she needs my help. Could u guys pls tell me wat the topic is abt??? and guide me to any links or presentations. thnx!!

Answer 1

Hybrid vigor is the term used to explain why when you cross two different inbred strains, the offspring generally have higher fitness than offspring of either of the respective strains.

One reason why this occurs is because of deleterious (negative) mutations that accumulate within the inbred lines, and by crossing them, you can eliminate some of those mutations.  Most evidence points to this being the primary reason for hybrid vigor.

But, for some traits, being heterozygous is advantageous over any homozygous condition.  This is true for traits where having two different alleles expands an individual's adaptation range (for example, temperature tolerance).  Since the inbred strains are highly homozygous, crossing two different highly homozygous strains will create a very heterozygous offspring.

One scientific paper that helps explain the genetics involved can be found at: http://www.pubmedcentral.nih.gov/article...

The references in this paper will give you further leads.

Answer 2

Hybrid vigor inbreeding, which is also known as heterosis, is a way of improving a specific characteristic of a hybrid.

From wiki:

Genetic basis of heterosis

Two leading hypotheses explain the genetic basis for fitness advantage in heterosis.

The overdominance hypothesis implies that the combination of divergent alleles at a particular locus will result in a higher fitness in the heterozygote than in the homozygote. Take the example of parasite resistance controlled by gene A, with two alleles A and a. The heterozygous individual will then be able to express a broader array of parasite resistance alleles and thus resist a broader array of parasites. The homozygous individual, on the other hand, will only express one allele of gene A (either A or a) and therefore will not resist as many parasites as the heterozygote.

The second hypothesis involves avoidance of deleterious recessive genes (also called the general dominance hypothesis), such that heterozygous individuals will express fewer deleterious recessive alleles than its homozygous counterpart.

The two hypotheses will have different consequences on the gene expression profile of the individuals. If over-dominance is the main cause for the fitness advantages of heterosis, then there should be an over-expression of certain genes in the heterozygous offspring compared to the homozygous parents. On the other hand, if avoidance of deleterious recessive genes is the cause, then there should be fewer genes that are under-expressed in the heterozygous offspring compared to the parents. Furthermore, for any given gene, the expression should be comparable to the one observed in the best of the two parents.

Hybrid vigor had been used in maize.