Genes exhibit independent assortment but do not act independently in their phenotypic expression. 

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#Unit 4. Cell Communication and Cell Signaling

MAD and MNT work with the SIN3 co-repressor protein to bring in histone deacetylases that help to block transcription

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#Unit 4. Cell Communication and Cell Signaling

A classic inherited cancer syndrome is retinoblastoma, which is caused by loss of function of RB.

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#Unit 4. Cell Communication and Cell Signaling

Children with hereditary (familial) retinoblastoma inherit one defective copy of the RB gene 

(sometimes seen as a small deletion on one of the two copies of chromosome 13)

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#Unit 4. Cell Communication and Cell Signaling

Sporadic retinoblastoma, inherit two normal RB alleles, each of which has undergone a LOF somatic mutation in a single retinal cell

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#Unit 4. Cell Communication and Cell Signaling

Subsequent loss or inactivation of the remaining normal allele in a somatic cell, known as loss of heterozygosity causes cancer to develop.

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#Unit 4. Cell Communication and Cell Signaling

Three mechanisms for LOH of tumor-suppressor genes:

Inactivating mutation or deletion

Chromosome missegregation

Mitotic recombination