{"id":1154,"date":"2012-09-06T13:54:24","date_gmt":"2012-09-06T01:54:24","guid":{"rendered":"https:\/\/blog.waikato.ac.nz\/bioblog\/2012\/09\/more_on_mosaics\/"},"modified":"2012-09-06T13:54:24","modified_gmt":"2012-09-06T01:54:24","slug":"more-on-mosaics","status":"publish","type":"post","link":"https:\/\/blog.waikato.ac.nz\/bioblog\/2012\/09\/more-on-mosaics\/","title":{"rendered":"more on mosaics"},"content":{"rendered":"

A couple of days ago I posted a stunning photo of a peacock<\/a>, and talked a bit about the possible genetic underpinnings of its colour patterns. My friend & blog-buddy Grant<\/a> then pointed me at the story of a cat<\/a> that has a similarly amazing colouration. Venus even has her own Facebook page<\/a>! (I will definitely be using both these images & their stories with my first-year class next week.)<\/p>\n

\"\"<\/a><\/p>\n

As you can see,  one half of Venus’s face is black, with a yellow eye, while the other half is orange – with a blue eye. What a stunning cat!<\/p>\n

The underlying reason for her striking colouration isn’t clear. She could be a chimera, formed from the fusion of two fertilised eggs, so that some of her cell lines would have different DNA from the rest. She could equally well be a particularly impressive example of the results of X-chromosome inactivation in female mammals<\/a>. In that case, of the two X chromosomes in the cells of the right-hand-side of Venus’s face, the one with the ‘orange’ allele would have been inactivated. That side of her face is black because all cells have functioning X chromosomes that are expressing the ‘black’ allele. The reverse would be true for the orange side of her face.<\/p>\n

Which leaves the question: why does she have a blue <\/i>eye on the orange side?<\/p>\n

In the comments thread to my original post, herr doktor bimler noted that<\/p>\n

\n

[the] X-chromosome mosaicism of female mammals turned up a lot in colour-vision research, because women carrying a colour-deficiency gene on one X chromosome end up with their retinas being more-or-less coarse patchworks of colour blindness. In the extreme case people can be red-green deficient in one eye and normal in the other**.<\/p>\n<\/blockquote>\n

This can also be true for haemophilia<\/a>, where the gene locus involved in the most common form of this disease is found on the X chromosome. (Haemophilia C is not sex-linked.<\/a>) Heterozygous women, with one normal and one recessive, deleterious allele, are regarded as carriers<\/a>, unaffected but with the potential to pass the ‘haemophilia’ allele on to some of their children, with damaging effect in those sons who receive it. But – and I must get my class to consider this one next week – such women are mosaics for X chromosome genes. If the ‘haemophilia’ X chromosome is ‘on’ in all the cells of their bone marrow, those women would also be haemophiliac.<\/p>\n

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<\/p>\n

**Being a person with a dry sense of humour, herr doktor concluded that such women "must spend their lives hiding from the colour vision researchers who wish to experiment upon them."<\/p>\n","protected":false},"excerpt":{"rendered":"

A couple of days ago I posted a stunning photo of a peacock, and talked a bit about the possible genetic underpinnings of its colour patterns. My friend & blog-buddy Grant then pointed me at the story of a cat that has a similarly amazing colouration. Venus even has her own Facebook page! (I will […]<\/p>\n","protected":false},"author":19,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"yoast_head":"\nmore on mosaics : BioBlog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blog.waikato.ac.nz\/bioblog\/2012\/09\/more-on-mosaics\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"more on mosaics : BioBlog\" \/>\n<meta property=\"og:description\" content=\"A couple of days ago I posted a stunning photo of a peacock, and talked a bit about the possible genetic underpinnings of its colour patterns. My friend & blog-buddy Grant then pointed me at the story of a cat that has a similarly amazing colouration. Venus even has her own Facebook page! 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