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Chapter 24 : Mendelian Genetics at the Molecular Level: An Example of Epistasis

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Mendelian Genetics at the Molecular Level: An Example of Epistasis, Page 1 of 2

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Abstract:

The black/brown coloration of Labrador retrievers is determined by whether their melanocytes can synthesize TYRP1 and thus convert brown eumelanin to black eumelanin. The yellow coat color is based on the ability of follicle melanocytes to receive a hormone signal that induces production of TYRP2 and TYRP1. These enzymes, which convert dopaquinone to the brown and black pigments, respectively, are not constitutively produced in melanocytes. Instead, the melanocytes receive a signal from the hormone melanocortin 1 (MC1) (also referred to as melanocyte-stimulating hormone), which causes the cell to produce the enzymes. The hormone signal is transmitted when the hormone binds to a membrane receptor protein, melanocortin 1 receptor (MC1R). The melanocytes of yellow Labs cannot receive the hormone signal to produce TYRP2 and TYRP1. Researchers took skin biopsies and used PCR to determine the protein-coding sequence of the TYRP1 gene. They found two common variants that could account for brown coat color—a premature stop codon in exon 5 and the deletion of a proline, also in exon 5—in addition to one less common variant.

Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24

Key Concept Ranking

Stop Codon
0.5142415
Membrane Protein
0.5111379
Surface Receptors
0.45836055
Amino Acids
0.45674145
Sequencing Methods
0.4565076
0.5142415
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Figures

Image of Figure 24.1
Figure 24.1

In black and chocolate Labs, MC1 binds to its receptor, MC1R, signaling the melanocyte to produce TYRP2 and TYRP1. The melanocyte can then synthesize black or brown pigment.

Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24
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Image of Figure 24.2
Figure 24.2

In yellow Labs, the MC1R is nonfunctional. MC1 cannot bind to it, and the hair follicle melanocytes never receive the signal to synthesize TYRP2 and TYRP1. The melanocytes therefore do not synthesize black or brown pigment. Instead, dopaquinone is converted into yellow phaeomelanin.

Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24
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Download as Powerpoint

References

/content/book/10.1128/9781555816100.chap24a
1. Everts, R. E.,, J. Rothuizen,, and B. A. van Oost. 2000. Identification of a premature stop codon in the melanocytestimulating hormone receptor gene (MC1R) in Labrador and Golden retrievers with yellow coat colour. Animal Genetics 31:194199.
2. Hoekstra, H.,, R. Hirschmann,, R. Bundey,, P. Insel,, and J. Crossland. 2006. A single amino acid mutation contributes to adaptive beach mouse color pattern. Science 313:101104.
3. Schmutz, S. M.,, T. G. Berryere,, and A. D. Goldfinch. 2002. TYRP1 and MC1R genotypes and their effects on coat color in dogs. Mammalian Genome 13:380387.

Tables

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Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24
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Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24
Generic image for table
Untitled

Possible gametes for parents with genotype BbRr

Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24
Generic image for table
Untitled

Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24
Generic image for table
Untitled

Citation: Kreuzer H, Massey A. 2008. Mendelian Genetics at the Molecular Level: An Example of Epistasis, p 343-349. In Molecular Biology and Biotechnology: A Guide for Teachers, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555816100.ch24

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