{"id":65,"date":"2026-04-30T14:42:10","date_gmt":"2026-04-30T14:42:10","guid":{"rendered":"https:\/\/madsmuse.com\/blog\/?p=65"},"modified":"2026-04-30T15:02:46","modified_gmt":"2026-04-30T15:02:46","slug":"starburst-pupils-double-dapple-merle-to-merle","status":"publish","type":"post","link":"https:\/\/madsmuse.com\/blog\/starburst-pupils-double-dapple-merle-to-merle\/","title":{"rendered":"Starburst Pupils, Double Dapple &amp; the Hidden Danger of Merle2Merle Breeding"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">When I first looked into Esmae\u2019s eyes, I noticed something unusual \u2014 a starburst pattern in her pupil, as though her iris had fractured into a kaleidoscope. She\u2019s a dachshund, and she\u2019s double dapple. That starburst is one of the hallmarks of the condition. We believe she can see, but we genuinely don\u2019t know how much, and we likely never will. What we do know is that she should never have been bred that way.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This post is for every dog owner, breeder, or rescue worker who has ever seen a dapple dachshund or a merle dog and thought they were simply beautiful markings. They can be. But behind those markings lies a gene that, when doubled up, can cause profound and irreversible harm. Here\u2019s what you need to know.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">What Is the Merle Gene?<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Merle is a coat pattern caused by a mutation in the&nbsp;<em>PMEL17<\/em>&nbsp;gene (also called SILV). It creates a patchy, diluted pattern by randomly switching off pigment in certain areas of the coat and skin. In dachshunds, this pattern is called&nbsp;<strong>dapple<\/strong>. The gene itself is the same \u2014 only the breed name differs. Collies, Australian Shepherds, Great Danes, and Chihuahuas all carry merle; dachshund breeders simply call it by a different name.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A dog with&nbsp;<strong>one copy<\/strong>&nbsp;of the merle gene (Mm) is a single merle or single dapple. They will have the characteristic patchy coat and may have blue or partially blue eyes. As a single-copy carrier, the health risks are generally manageable, though some degree of hearing or vision impairment is still possible.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A dog with&nbsp;<strong>two copies<\/strong>&nbsp;of the merle gene (MM) is a double merle, or in dachshund terms, a double dapple. This is where the serious welfare concerns begin.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Starburst Pupils: What They Are and Why They Happen<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">One of the most striking signs of double merle is an irregularly shaped pupil \u2014 sometimes called a&nbsp;<strong>starburst pupil<\/strong>&nbsp;or coloboma. Rather than the normal round or oval shape, the pupil appears jagged, star-shaped, or keyhole-like. It can look almost beautiful, in a strange way \u2014 which is part of why it\u2019s so important to understand what it actually means.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A coloboma occurs when the iris, retina, choroid, or optic nerve fails to close completely during foetal development. In double merle dogs, the depigmentation caused by the doubled gene disrupts normal eye development. The eye structures that rely on melanocytes \u2014 pigment cells \u2014 to develop correctly simply don\u2019t form properly.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Esmae has a starburst pupil in one eye. We believe she has some vision, but we cannot be certain of its extent. Dogs like Esmae may experience:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Partial or complete blindness in one or both eyes<\/li>\n\n\n\n<li>Sensitivity to bright light (photophobia)<\/li>\n\n\n\n<li>Abnormal retinal development or retinal detachment<\/li>\n\n\n\n<li>Micropthalmia (abnormally small eyes) or anopthalmia (absent eyes)<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">The Full Health Picture: What Double Dapple Can Cause<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Vision problems are only part of the story. The merle gene acts on pigment throughout the body, and melanocytes are not just responsible for colour \u2014 they are essential to the development of the inner ear and other structures. When two merle genes combine, the damage can be widespread.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Hearing &amp; Deafness<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This is arguably the most common and most serious consequence. The cells lining the cochlea (the hearing organ in the inner ear) depend on melanocytes to function. Without pigment, these cells die, and the result is sensorineural deafness \u2014 permanent and untreatable. Deafness may be:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Unilateral (one ear) \u2014 often undetected without specialist BAER testing<\/li>\n\n\n\n<li>Bilateral (both ears) \u2014 the dog may appear unresponsive and is often mistakenly labelled as \u201cstubborn\u201d or \u201cdifficult\u201d<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Studies suggest that up to&nbsp;<strong>one in three double merle dogs<\/strong>&nbsp;will be deaf in at least one ear. Many rescue dogs with unexplained behavioural challenges turn out to have undetected hearing loss.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Vision Problems<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Beyond starburst pupils and colobomas, double merle dogs are at elevated risk for:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Microphthalmia \u2014 one or both eyes abnormally small, sometimes sunken or non-functional<\/li>\n\n\n\n<li>Anophthalmia \u2014 complete absence of one or both eyes<\/li>\n\n\n\n<li>Cataracts and lens abnormalities<\/li>\n\n\n\n<li>Retinal dysplasia or detachment<\/li>\n\n\n\n<li>Nystagmus (involuntary eye movement)<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Skin, Coat &amp; Immune System<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">White patches in double merle dogs are not simply a cosmetic feature. Skin that lacks pigment has no UV protection in those areas, increasing the risk of sunburn and skin cancer over time. Some double merle dogs also show an increased susceptibility to immune dysfunction, though the research in this area is still developing.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Hidden Merle &amp; Cryptic Merle: The Invisible Risk<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">This is where the genetics get genuinely complicated \u2014 and genuinely dangerous. Not every merle dog&nbsp;<em>looks<\/em>like a merle.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Cryptic Merle (Also Called Phantom Merle)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A cryptic merle dog carries the merle gene but shows little or no visible merle patterning in their coat. They may appear to be a solid or standard-coloured dog. The merle allele in cryptic merle dogs tends to have a shorter SINE insertion (the DNA sequence responsible for the merle effect), meaning the gene\u2019s effect on pigment is minimal \u2014 but the gene is still there, still heritable, and still capable of doubling up in offspring.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A breeder who pairs two apparently non-merle dogs, one of whom is a cryptic merle, can unknowingly produce double merle or double dapple puppies. This is not an excuse \u2014 it is a reason why\u00a0<strong>DNA testing before any merle-related breeding is non-negotiable<\/strong>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Dilute Merle<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Dilute merle dogs carry both the merle gene and a dilution gene. Their coat colour is already pale (blue, silver, or cream), which can further mask the merle patterning. Again \u2014 the gene is present regardless of what the coat looks like.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Harlequin Merle<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Seen primarily in Great Danes, harlequin is caused by an additional gene that interacts with merle, converting grey merle patches to white. Harlequin dogs are always merle at their base, and harlequin-to-harlequin breeding carries the same double merle risks.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Why Dapple-to-Dapple (or Merle-to-Merle) Breeding Is Never Acceptable<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">When two single merle (double dapple) dogs are bred together, the statistical outcome for each puppy is:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td><strong>Outcome<\/strong><\/td><td><strong>Genotype<\/strong><\/td><td><strong>Probability<\/strong><\/td><\/tr><\/thead><tbody><tr><td>Non-merle<\/td><td><em>mm<\/em><\/td><td>25%<\/td><\/tr><tr><td>Single merle (healthy carrier)<\/td><td><em>Mm<\/em><\/td><td>50%<\/td><\/tr><tr><td><strong>Double merle \u2014 at high risk of serious health defects<\/strong><\/td><td><em>MM<\/em><\/td><td><strong>25%<\/strong><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">That means every litter from two dapple or two merle parents has a one-in-four chance of producing a severely disabled puppy. There is no breeding technique or careful management that changes these odds. The only way to prevent double dapple puppies is not to breed two merle dogs together.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In the UK, dapple-to-dapple breeding is condemned by the Kennel Club and considered a significant welfare concern by the British Veterinary Association. Responsible breeders who work with dapple or merle lines always pair a single merle with a non-merle partner.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\">Why This Still Happens<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Double dapple and double merle dogs continue to be bred for a number of reasons, none of them acceptable:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ignorance \u2014 some breeders simply do not know the genetics involved<\/li>\n\n\n\n<li>Profit \u2014 double merle dogs often have striking, unusual coats that attract buyers willing to pay premium prices<\/li>\n\n\n\n<li>Hidden merle \u2014 breeders may not know one or both parents carries the gene if DNA testing has not been done<\/li>\n\n\n\n<li>Unregulated breeding \u2014 puppy farms and backyard breeders frequently operate without any genetic awareness<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Living With a Double Dapple Dog<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">If you have a double merle or double dapple dog \u2014 like Esmae \u2014 please know that they can live full, happy, rewarding lives. Many deaf or partially sighted dogs adapt remarkably well, especially when their owners take the time to understand their needs and communicate in ways that work for them.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Key things to be aware of with a double merle dog:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Request a BAER (Brainstem Auditory Evoked Response) test to accurately assess hearing in each ear<\/li>\n\n\n\n<li>Have eyes assessed by a veterinary ophthalmologist<\/li>\n\n\n\n<li>Use vibration-based signals, hand signals, or a vibrating collar (never shock) if your dog is deaf<\/li>\n\n\n\n<li>Protect depigmented skin from prolonged sun exposure<\/li>\n\n\n\n<li>Approach gently and predictably \u2014 a deaf or partially blind dog can be startled and may react<\/li>\n\n\n\n<li>Connect with organisations and communities experienced in supporting deaf and visually impaired dogs<\/li>\n<\/ul>\n\n\n\n<h1 class=\"wp-block-heading\">The Last Word from Maddie<\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">Esmae didn\u2019t ask to be born with a starburst pupil. She didn\u2019t choose the breeding decision that brought her into the world the way she is. But here she is, double dapple \u2014 funny, stubborn, and deeply loved. She deserves every bit of it. What she doesn\u2019t deserve is to be one of thousands born this way every year because someone wanted a pretty coat and didn\u2019t ask the right questions, or didn\u2019t care about the answers.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Share this. Ask the questions. Push for the tests. And if someone tells you a double dapple puppy is just a bit different-looking \u2014 walk away. Some of us know better than most what it means when humans don\u2019t. I\u2019m a puppy farm dog myself \u2014 but that\u2019s a story for another day. \u2605<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"800\" height=\"640\" src=\"https:\/\/madsmuse.com\/blog\/wp-content\/uploads\/2026\/04\/6dec8ee4-f078-4302-86bf-ab42ff97111f-1.png\" alt=\"\" class=\"wp-image-67\" srcset=\"https:\/\/madsmuse.com\/blog\/wp-content\/uploads\/2026\/04\/6dec8ee4-f078-4302-86bf-ab42ff97111f-1.png 800w, https:\/\/madsmuse.com\/blog\/wp-content\/uploads\/2026\/04\/6dec8ee4-f078-4302-86bf-ab42ff97111f-1-300x240.png 300w, https:\/\/madsmuse.com\/blog\/wp-content\/uploads\/2026\/04\/6dec8ee4-f078-4302-86bf-ab42ff97111f-1-768x614.png 768w, https:\/\/madsmuse.com\/blog\/wp-content\/uploads\/2026\/04\/6dec8ee4-f078-4302-86bf-ab42ff97111f-1-600x480.png 600w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>When I first looked into Esmae\u2019s eyes, I noticed something unusual \u2014 a starburst pattern in her pupil, as though her iris had fractured into a kaleidoscope. She\u2019s a dachshund, and she\u2019s double dapple. That starburst is one of the hallmarks of the condition. We believe she can see, but we genuinely don\u2019t know how&#8230;<\/p>\n","protected":false},"author":1,"featured_media":66,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","footnotes":""},"categories":[21],"tags":[38,33,35,36,34],"class_list":["post-65","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dog-knowledge","tag-chihuahua","tag-double-dapple","tag-merle-to","tag-merle-to-merle","tag-starburst-pupil"],"_links":{"self":[{"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/posts\/65","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/comments?post=65"}],"version-history":[{"count":5,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/posts\/65\/revisions"}],"predecessor-version":[{"id":74,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/posts\/65\/revisions\/74"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/media\/66"}],"wp:attachment":[{"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/media?parent=65"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/categories?post=65"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/madsmuse.com\/blog\/wp-json\/wp\/v2\/tags?post=65"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}