BIOL 1F90 Lecture Notes - Lecture 25: X-Inactivation, Barr Body, Genomic Imprinting

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greyantelope7

21 Jan 2016

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Calico cat coat color pattern: calico pattern is explained by the permanent inactivation of one, x-linked gene for coat color. Initiation and spreading occur only during embryonic development individual"s life. Involves a single gene, part of a chromosome, an entire chromosome, or all the chromosomes from one parent. Igf-2 gene example, insulin-like growth factor: offspring distinguished between maternally and paternally, offspring express either the maternal or paternal allele, but not. Igf-2 growth factor- absence of this growth factor will not grow to full height. Slide 98 (first image) both copies don"t make growth factor, in this case this individual is female and this female pairs with a male with two copies, homozygous female with a normal homozygous male. The offspring has one with the copy and one without (heterozygous) allele from female is turned off, allele from father is the active one.

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Could you help me out with question b? Please provide explanation as well.

7. a. Explain why the typical calico cat is a female with individual patches of orange and black fur. (Be sure to account for the mosaic phenotype.)

Answer: Calico cat has two patches of orange and black fur due to the alleles being present in the X chromosomes. As the female has XX chromosomes, they are able to present both colours. In detail, this is due to X chromosome inactivation. The X chromosome bearing the orange allele is activated when the black allele is inactivated and the black allele is activated when the orange allele is inactivated. The heterozygous female that has both alleles associated with the X chromosome shows mosaic pattern because X chromosome containing orange allele is activated and black allele is activated.

b. What is the underlying process an example of and what does it accomplish in terms of gene expression (i.e., why is it important to the cell/organism)? Answer:

aquamarinedeer796

		None of the females
		1/2 of the females
		All of the females
		Either 1/2 or none of the females depending on whether the black male cat was homozygous for black or heterozygous.

X-inactivation in mammals can lead to mosaic coloration if the gene governing coat color is on the X chromosome. This occurs with cats and can lead to the calico coat color on the back, a mosaic of orange and black patches. If a calico coat female and a black coat male mate and have kittens, what fraction of their female kittens will have a calico coat?

(4)7. Dosage compensation leads to a variety of interesting coat color patterns in certain mammals. For instance, a female cat that is heterozygous for two coat color alleles, say black and orange, will usually have the "calico" or mosaic phenotype. Describe the chromosomal basis for the mosaicism (calico) in the female. Explain why chromosomally normal male cats do not show the mosaic phenotype, but XXY male cats can be calico.

BIOL 1F90 Lecture Notes - Lecture 25: X-Inactivation, Barr Body, Genomic Imprinting

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