Genetics: Inbreeding and Linebreeding

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Questions and Answers

Inbreeding depression is mainly associated with a decline in:

Performance and vigor

What is the main difference between linebreeding and intensive inbreeding?

Whether they involve mating of closely related animals

What effect does inbreeding have on the number of pairs of genes existing in the homozygous state?

Increases the number of pairs

Which situation would lead to a higher rate of homozygosity due to inbreeding?

Mating of closely related animals Signup and view all the answers

What is not increased by inbreeding in a population?

Recessive alleles Signup and view all the answers

In terms of genetic effects, what is a common consequence of intense inbreeding?

Reduced performance and vigor Signup and view all the answers

What is the term for mating of unrelated animals within the same breed or from two different lines of the same breed?

Linecrossing Signup and view all the answers

What is the least common form of outbreeding due to animals from different species normally not interbreeding?

Species cross Signup and view all the answers

Which mating practice involves the mating of purebred sires to commercial grade females?

Grading up Signup and view all the answers

What effect does outbreeding have on the proportion of genes that are homozygous?

Decreases the proportion Signup and view all the answers

When unrelated animals are mated, what advantage is observed in their progeny?

Hybrid vigor or heterosis Signup and view all the answers

What defines a situation where two animals do not share a common ancestor for at least 5 generations?

Outbreeding Signup and view all the answers

What is one of the adverse effects of inbreeding mentioned in the text?

Slower growth rates Signup and view all the answers

How do recessive genes primarily contribute to the adverse effects of inbreeding?

By causing deficiencies in important enzymes Signup and view all the answers

What is a practical use of inbreeding mentioned in the text?

To uncover and eliminate detrimental recessive genes Signup and view all the answers

Why are more pairs of recessive genes expected to occur among inbred animals?

As the incidence of homozygotes increases Signup and view all the answers

What type of genes contribute significantly to inbreeding depression according to the text?

Non-additive genes Signup and view all the answers

How can inbreeding be beneficial when used in conjunction with selection?

It increases homozygosity of favorable genes Signup and view all the answers

Study Notes

Inbreeding

The more closely related the parents, the more inbred the offspring will be.
Intensive inbreeding involves mating of closely related animals that can be traced to more than one common ancestor.
Linebreeding is a type of inbreeding where relatives are chosen due to a particular common ancestor to incorporate as many genes as possible from a superior ancestor.

Genetic Effect of Inbreeding

Inbreeding increases the number of pairs of genes that exist in the homozygous state.
The rate of homozygosity increase depends on the closeness of relationship between parents.

Consequences of Homozygosity

Inbreeding does not increase the number of recessive alleles in the population, but increases homozygosity regardless of phenotypic expression.
Inbreeding is often associated with a decline in performance and vigor, and occasional appearance of genetic defects in animals (inbreeding depression).

Phenotypic Effects of Inbreeding

Inbreeding can lead to stillbirth, mummification, reduced fertility, increased deaths, susceptibility to disease, and slower growth rates due to recessive genes.

Outbreeding

Outbreeding increases the proportion of genes that are heterozygous and reduces the proportion that are homozygous.
Categories of outbreeding include linecrossing, breedcrossing, grading up, species cross, and random mating.

Genetic Effect of Outbreeding

Crossbreeding generally results in a more rapid increase in heterozygosity because the breeds are less likely to be related to one another.

Phenotypic Effect of Outbreeding

When unrelated animals are mated, their progeny tend to perform better due to hybrid vigor or heterosis.

Uses of Inbreeding

Inbreeding can be used along with selection to uncover and eliminate detrimental recessive genes.
It can increase homozygosity of favorable genes, and the best-performing animals can be retained for breeding purposes.
Inbreeding can be used to produce inbred lines for outcrossing programs, and benefits can be obtained when used in conjunction with selection.

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