{"id":1435,"date":"2020-08-06T23:55:26","date_gmt":"2020-08-06T23:55:26","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/transmission-genetics\/epistasis\/"},"modified":"2021-01-31T23:19:53","modified_gmt":"2021-01-31T22:19:53","slug":"epistasis","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/transmission-genetics\/epistasis\/","title":{"rendered":"Epistasis"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><div class=\"intro\"><strong>Epistasis<\/strong> is a <strong>Non-Mendelian<\/strong> phenomenon where the expression of one gene\/trait is dependent on the expression of another gene\/trait i.e. the gene will only be expressed in the presence\/absence of another one.<\/div><\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>It is non-mendelian because from <strong>Mendel&#8217;s second law<\/strong>; <strong>The Law of Independent Assortment<\/strong>, genes are supposed to be inherited independently. This is an example of gene interaction.<\/li><li>The gene that is being masked is the <strong>hypostatic<\/strong> gene while the gene influencing the expression of the hypostatic gene is known as the <strong>epistatic<\/strong> gene<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Epistasis can be;<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>Dominant<\/li><li>Recessive<\/li><\/ol>\n\n\n<span class=\"block-heading\" id=\"header_1\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Dominant Epistasis<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_1\">\n\n\n<p class=\"wp-block-paragraph\">This is when the <strong>epistatic<\/strong> allele is a dominant allele.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>In this case, expression of the epistatic gene in homozygous dominant or heterozygous form is enough to inhibit the expression of the hypostatic gene.<\/li><li>Expression of the epistatic gene in <strong>homozygous recessive form has no effect<\/strong> and in this case, the hypostatic gene will be expressed.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">I will give an example below:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Summer squash is a fruit that has three colours; white, yellow and green. The <strong>yellow trait(Y)<\/strong> is dominant while <strong>green(y)<\/strong> is recessive. The <strong>&#8216;W&#8217; gene codes for the white colour<\/strong> and is dominantly epistatic to the &#8216;Y&#8217; gene.&nbsp; This means once the dominant W allele is present, no colour will be expressed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">W___ codes for white squash, wwY_ codes for yellow squash and wwyy codes for green squash<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">To further explain, I will make a cross between two <strong>heterozygous<\/strong> white plants<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Parental phenotypes:&nbsp; &nbsp; &nbsp; &nbsp; White\u00d7White<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Parental genotypes:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;WwYy\u00d7WwYy<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Parental gametes:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; (WY)(Wy)(wY)(wy)\u00d7(WY)(Wy)(wY)(wy)<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"pure-table\"><tbody><tr><td>&nbsp;<\/td><td>(WY)<\/td><td>(Wy)<\/td><td>(wY)<\/td><td>(wy)<\/td><\/tr><tr><td>(WY)<\/td><td>WWYY<\/td><td>WWYy<\/td><td>WwYY<\/td><td>WwYy<\/td><\/tr><tr><td>(Wy)<\/td><td>WWYy<\/td><td>WWyy<\/td><td>WwYy<\/td><td>Wwyy<\/td><\/tr><tr><td>(wY)<\/td><td>WwYY<\/td><td>WwYy<\/td><td>wwYY<\/td><td>wwYy<\/td><\/tr><tr><td>(wy)<\/td><td>WwYy<\/td><td>Wwyy<\/td><td>wwYy<\/td><td>wwyy<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">F1 phenotypes:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;White:Yellow: Green<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Phenotypic ratio:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 12:3:1<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In summary:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Plants without colour: Plants with colour<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">12:4<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The 12:4 ratio seen is characteristic for dominant epistasis.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">As seen above, as long as the dominant &#8216;W&#8217; allele is expressed, it does not matter what the other alleles are, the colour of the fruit will be white. Yellow and Green will only be expressed in the presence of recessive &#8216;w&#8217; allele as it has no effect on colour. In this case, yellow is dominant and green is recessive.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Since &#8216;W&#8217; gene affects the expression of &#8216;Y&#8217; gene, it is said to be <strong>epistatic<\/strong> and Y gene is <strong>hypostatic<\/strong>.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_2\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Recessive Epistasis<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_2\">\n\n\n<p class=\"wp-block-paragraph\">This is when the <strong>epistatic<\/strong> allele is a recessive allele.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>In this case, expression of the epistatic gene in <strong>homozygous dominant or heterozygous form<\/strong> <strong>has no effect<\/strong> and the <strong>hypostatic<\/strong> gene will be expressed.<\/li><li>Expression of the epistatic gene in <strong>homozygous recessive form is enough to inhibit the expression<\/strong> of the hypostatic gene.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">I will give an example below;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>ABO blood group system<\/strong> is one used to classify blood according to the carbohydrate antigens present on the surface of red blood cells present in the blood <em>(details on the ABO blood group systems are discussed in the Polymorphism: Blood Groups: ABO blood groups course. It is highly recommended that you stop here, go read that course and come back here).&nbsp;<\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Let us cross make a cross between two <strong>heterozygotes<\/strong> with blood groups A and B.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Parental phenotype:&nbsp; &nbsp; &nbsp; &nbsp;A\u00d7B<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Parental genotype:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;I<sup>A<\/sup>iHh\u00d7I<sup>B<\/sup>iHh<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Parental gametes:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(I<sup>A<\/sup>H)(I<sup>A<\/sup>h)(iH)(ih)\u00d7(I<sup>B<\/sup>H)(I<sup>B<\/sup>h)(iH)(ih)<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"pure-table\"><tbody><tr><td>&nbsp;<\/td><td>(I<sup>B<\/sup>H)<\/td><td>(I<sup>B<\/sup>h)<\/td><td>(iH)<\/td><td>(ih)<\/td><\/tr><tr><td>(I<sup>A<\/sup>H)<\/td><td>I<sup>A<\/sup>I<sup>B<\/sup>HH<\/td><td>&nbsp;I<sup>A<\/sup>I<sup>B<\/sup>Hh<\/td><td>I<sup>A<\/sup>iHH<\/td><td>I<sup>A<\/sup>iHh<\/td><\/tr><tr><td>(I<sup>A<\/sup>h)<\/td><td>I<sup>A<\/sup>I<sup>B<\/sup>Hh<\/td><td>&nbsp;I<sup>A<\/sup>I<sup>B<\/sup>hh<\/td><td>I<sup>A<\/sup>iHh<\/td><td>I<sup>A<\/sup>ihh<\/td><\/tr><tr><td>(iH)<\/td><td>I<sup>B<\/sup>iHH<\/td><td>I<sup>B<\/sup>iHh<\/td><td>iiHH<\/td><td>iiHh<\/td><\/tr><tr><td>(ih)<\/td><td>&nbsp;I<sup>B<\/sup>iHh<\/td><td>I<sup>B<\/sup>ihh<\/td><td>iiHh<\/td><td>iihh<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">F1 phenotype:&nbsp; &nbsp; &nbsp;A:B: AB:O: Bombay<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Phenotypic ratio:&nbsp; &nbsp;3:3:3:3:4<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In summary:&nbsp; &nbsp; ABO antigen and H antigen present:&nbsp; &nbsp;Only H antigen present:&nbsp; &nbsp;No antigen present<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">9:3:4<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The 9:3:4 ratio seen is characteristic for recessive epistasis. The &#8216;H&#8217; gene is <strong>epistatic<\/strong> while the &#8216;ABO&#8217; gene is <strong>hypostatic<\/strong>.<\/p>\n<\/span><div id=\"the_titles\" style=\"display:none;\"><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Dominant Epistasis<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Recessive Epistasis<\/h4><\/div>","protected":false},"excerpt":{"rendered":"<p>It is non-mendelian because from Mendel&#8217;s second law; The Law of Independent Assortment, genes are supposed to be inherited independently. This is an example of gene interaction. The gene that is being masked is the hypostatic gene while the gene influencing the expression of the hypostatic gene is known as the epistatic gene Epistasis can [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1346,"menu_order":5,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1435","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.8 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Epistasis &#8211; Meddists<\/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:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/transmission-genetics\/epistasis\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/medical-genetics\\\/transmission-genetics\\\/epistasis\\\/\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/medical-genetics\\\/transmission-genetics\\\/epistasis\\\/\",\"name\":\"Epistasis &#8211; 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