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Overview of Mendelian and non-Mendelian genetics

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A farmer breeds a champion bull with a good quality cow of the same breed.
Discuss why the offspring from the champion bull may not necessarily have the attributes to become champions themselves. Include simple diagrams and describe how the characters resulting in a favourable phenotype arise and the importance of combinations of genes in the expression of phenotypic characters. Explain the processes involved in the inheritance of characteristics

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The inheritance of genetic traits is determined by a number of factors. First, you must determine how the trait is inherited. Because the offspring come from breeding the champion bull with a cow that has it's own genetic contribution, you needed to know how the two genomes are going to interact to produce the offspring. I will start with the simplest scenarios and increase in complexity.

Some traits are accounted for by single genes with two alleles in a dominant recessive relationship. The desired trait might be the dominant allele in which case only a single copy of the allele from the champion bull will produce the trait in the offspring.
A = desired allele
a = other allele

Champion bull is Aa or AA. Dam may be aa, Aa, or AA. Draw out each cross to see the outcome. If bull is Aa and Dam is aa. Then 3/4 of the possible offspring carry the desired trait and 1/4 do not.

If the desired trait is a result of the recessive allele, then the probabilities change.
a = desired allele
A = other allele

Champion bull must be aa and Dam can be aa, Aa, AA. If the bull (aa) is bred to the dam AA, then all of the offspring will be Aa and non will carry the desired trait inherited as aa.

The above case applies to autosomal genes. It may be that the desired trait is carried on the sex chromosomes. If this is the case then inheritance of the desired allele is tied to gender. Again the desired allele may be either dominant or negative.
XA = desired allele
Xa or Y = other allele

The champion bull (XAY) bred to a dam (XaXa) will ...

Solution Summary

Several paragraphs explaining how Mendelian and non-Mendelian genetics account for diversity in cattle traits. Web references provided.

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