farm:colour_genetics
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A Primer on Colour Genetics
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<tr> <td colspan="4"> <font color="#fff494" face="verdana"><b>A Short lesson on colour genetics in ducks.</b></font> </td> </tr> <tr> <td colspan="4" bgcolor="#fff494"><font color="black" face="verdana" size="-1"><b>First, a bit of background:</b><br> <br> </font><font face="verdana" size="-1">Genes come in pairs - for each new baby (or seed) one half of each pair is supplied by the mom, and the other half by the dad. When referring to the two genes that occur on the same place (</font><font color="#006600" face="verdana" size="-1"><b>locus</b></font><font face="verdana" size="-1">) on each of a pair of chromosomes, we can also call them </font><font color="#006600" face="verdana" size="-1"><b>alleles</b></font><font face="verdana" size="-1">. <br> <br> If both alleles of a gene pair are the same, then it is called </font><font color="#006600" face="verdana" size="-1"><b>homozygous</b></font><font face="verdana" size="-1"> (homo = same), but if they are different it is called </font><font color="#006600" face="verdana" size="-1"><b>heterozygous</b></font><font face="verdana" size="-1"> (hetero = different).<br> <br> The way that these pairs express themselves is called the </font><font color="#006600" face="verdana" size="-1"><b>phenotype</b></font><font face="verdana" size="-1">, and the actual pair combination is called the </font><font color="#006600" face="verdana" size="-1"><b>genotype</b></font><font face="verdana" size="-1">. They don't need to be the same. Sometimes, especially when the organism is homozygous for that gene pair, the genotype and phenotype seem to match up. That basically means that what you see is what you get. In the ducks example, if you see it looks like a chocolate Appleyard, then it is homozygous for the chocolate factor gene. In this case it HAS to be homozygous because the brown factor is recessive to black.<br> <br>Although this is somewhat of an oversimplification, it will do for our purposes. Genes have two main ways of "coexisting":</font> <ol> <li><font face="verdana" size="-1"><font face="verdana" size="-1"><b>As a dominant / recessive pair: </b>in this case the dominant one is the one whose effects are seen, and the recessive one is like a silent partner. When we write them down, dominant genes are usually written as capital letters (B), and recessive ones as small letters (b).</font></font> </li><li><font face="verdana" size="-1"><b>As a co-dominant or incompletely dominant pair: </b>in this case they will tend to "share" expression and you may see the effects of both in the phenotype. In incomplete dominance the expression is blended (like white & red to make pink), while with co-dominance they share (like white and red to make red-and-white patches, stripes, etc.).</font> </li></ol> </td></tr> </tbody></table>
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The Black vs. Chocolate gene
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<tbody><tr><td bgcolor="#fff494"> <p><font color="black" face="verdana" size="-1">In most animals, there is a gene that controls the "black factor" in their colour. This doesn't mean that they will be all black, unless they are solid coloured to begin with. In animals with multiple colours in their coats, it controls whether the darkest colour will be black or brown (sometimes called chocolate). What it really controls is the eumelanin pigment: specifically, the a protein that makes up the pigment granule.<br> </font></p> <table bgcolor="#cc3300" border="0" cellpadding="1" cellspacing="1"> <tbody><tr> <td align=“center” bgcolor="#fff494"> <font face="verdana" size="-1">Here's how it expresses itself in rabbits. The one on the left is black, and the one on the right is chocolate. The white colouring (called a "broken pattern" in rabbits) is the result of a different pair of genes.</font> </td> <td align=“center” bgcolor="#fff494"> <font face="verdana" size="-1"><img src=" lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-kiana-28-02-04.JPG" alt="" border="0" height="145" width="150"></font> </td> <td align=“center” bgcolor="#fff494"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:tn-rx-jewel-04-01-08-1.JPG" alt="" border="0" height="145"></td> </tr> </tbody></table> <p><font face="verdana" size="-1">The chocolate colouring is a simple recessive to "black", which is dominant, so it is possible for chocolate babies to show up in an otherwise "normal" flock. Both the duck and the drake must carry the chocolate gene, and then it is expected that about 1/4 of their babies will end up chocolate. However, if you breed two chocolates together you can never get a black baby.<br> <br> <br> The chart below shows how the genes will be combined. <br> There are essentially four possibilities: BB, Bb, bB (which is usually written Bb as well), and bb.<br> If one parent supplies the 'B', then the baby will look black (its phenotype), no matter what the other parent supplies. If the other parent supplies a 'B' also, then the baby is homozygous, and the phenotype and genotypes match. BUT, if the other parent supplies a 'b', then the baby will LOOK black, in other words, its phenotype will be black, but its genotype is heterozygous.<br> If both parents supply a 'b', then the baby will be brown, and because brown is recessive, you can be sure that it is homozygous for this trait.</font></p> <div align="left"> <dl> <dt><font face="verdana" size="-1"><b>B = black<br> b = chocolate<br> </b></font> </dt><dt><font face="verdana" size="-1">BB and Bb will <i>appear</i> black, while bb looks chocolate.<br> BB can produce only blacks, no matter what it is mated with, because it will always provide a black allele. Some will be homozygous and others will be heterozygous<br> </font> </dt><dt><font face="verdana" size="-1">bb can produce only chocolates, if it is mated to another chocolate.<br> <br> </font> </dt></dl> </div> <table bgcolor="#cc3300" border="0" cellpadding="1" cellspacing="1"> <tbody><tr> <td rowspan="4" bgcolor="#fff494"></td> <td colspan="4" bgcolor="#fff494"> <font face="verdana"><b>black X black</b></font> </td> <td rowspan="6" bgcolor="#fff494" width="15"> </td> <td colspan="4" bgcolor="#fff494"> <font face="verdana"><b>black X black</b></font> </td> <td rowspan="6" bgcolor="#fff494" width="15"> </td> <td colspan="4" bgcolor="#fff494"> <font face="verdana"><b>black X brown</b></font> </td> </tr> <tr> <td rowspan="3" bgcolor="#fff494"> <font face="verdana"><b>BB X BB</b></font> </td> <td rowspan="5" bgcolor="#fff494"></td> <td colspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele supplied<br> by parent#1</font> </td> <td rowspan="3" bgcolor="#fff494"> <font face="verdana"><b>BB X Bb</b></font> </td> <td rowspan="5" bgcolor="#fff494"></td> <td colspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele supplied<br> by parent#1</font> </td> <td rowspan="3" bgcolor="#fff494"> <font face="verdana"><b>BB X bb</b></font> </td> <td rowspan="5" bgcolor="#fff494"></td> <td colspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele supplied<br> by parent#1</font> </td> </tr> <tr height="18"> <td align=“center” bgcolor="black" height="18"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black" height="18"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black" height="18"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> </tr> <tr height="5"> <td colspan="2" bgcolor="#fff494" height="5"></td> <td colspan="2" bgcolor="#fff494" height="5"></td> <td colspan="2" bgcolor="#fff494" height="5"></td> </tr> <tr> <td rowspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele<br> supplied by<br> parent#2</font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> </tr> <tr> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> </tr> </tbody></table> <p></p> <table bgcolor="#cc3300" border="0" cellpadding="1" cellspacing="1"> <tbody><tr> <td rowspan="4" bgcolor="#fff494"></td> <td colspan="4" bgcolor="#fff494"> <font face="verdana"><b>black X black</b></font> </td> <td rowspan="6" bgcolor="#fff494" width="15">
</td> <td colspan="4" bgcolor="#fff494"> <font face="verdana"><b>black X brown</b></font> </td> <td rowspan="6" bgcolor="#fff494" width="15"> </td> <td colspan="4" bgcolor="#fff494"> <font face="verdana"><b>brown X brown</b></font> </td> </tr> <tr> <td rowspan="3" bgcolor="#fff494"> <font face="verdana"><b>Bb X Bb</b></font> </td> <td rowspan="5" bgcolor="#fff494"></td> <td colspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele supplied<br> by parent#1</font> </td> <td rowspan="3" bgcolor="#fff494"> <font face="verdana"><b>Bb X bb</b></font> </td> <td rowspan="5" bgcolor="#fff494"></td> <td colspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele supplied<br> by parent#1</font> </td> <td rowspan="3" bgcolor="#fff494"> <font face="verdana"><b>bb X bb</b></font> </td> <td rowspan="5" bgcolor="#fff494"></td> <td colspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele supplied<br> by parent#1</font> </td> </tr> <tr height="18"> <td align=“center” bgcolor="black" height="18"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600" height="18"> <font color="#fff494" face="verdana"><b>b</b></font> </td> </tr> <tr height="5"> <td colspan="2" bgcolor="#fff494" height="5"></td> <td colspan="2" bgcolor="#fff494" height="5"></td> <td colspan="2" bgcolor="#fff494" height="5"></td> </tr> <tr> <td rowspan="2" bgcolor="#fff494"> <font face="verdana" size="-1">Allele<br> supplied by<br> parent#2</font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>BB</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>B</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> </tr> <tr> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="black"> <font color="#fff494" face="verdana"><b>Bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>b</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> <td align=“center” bgcolor="#996600"> <font color="#fff494" face="verdana"><b>bb</b></font> </td> </tr> </tbody></table> <div align="left"> <dl> <dt><font face="verdana" size="-1"><b>B = black<br> b = chocolate<br> </b></font> </dt><dt><font face="verdana" size="-1">BB and Bb will <i>appear</i> black, while bb looks chocolate.<br>BB can produce only blacks, no matter what it is mated with, because it will always provide a black allele. Some will be homozygous and others will be heterozygous, depending entirely on the genetic makeup of the other parent.<br> </font> </dt><dt><font face="verdana" size="-1">bb can produce only chocolates, when it is mated to another chocolate.<br> <br>Each combination has an equal chance of happening for each set of parents.<br> There are four possibilities, so each one has a 25% chance of happening. <br> This means if both parents are heterogygous (<b>Bb)</b>, we have: <b>25% BB</b>, <b>25% Bb</b>, <b>25% bB</b>, <b>25% bb</b>. Half of the babies will be either Bb or bB, so we combine them when we write it out. <br> That gives us: <b>25% BB</b>, <b>50% Bb</b>, and <b>25% bb</b>. Those are the GENOTYPES.<br> <br> If we look at the phenotypes (all we can actually examine from the outside), we see: 75% black, 25% brown, since both the BB and Bb will LOOK black.<br> The way to tell if a black is heterogygius or homozygous, is to mate it with a brown. If ANY brown babies are born, you can be sure it is heterozygous for black. However, if it only produces black, you still don't know. "Equal chance" means EVERY baby has the same chances of being one or another. It is possible that all babies ended up being BB and Bb. The more babies you produce, the closer to the "predicted distribution" we are likely to get. It's like tossing a coin or rolling a die for each baby individually though. Even though it seems very unlikely, it is STILL POSSIBLE to roll the die 900 times and get 900 6's.</font> </dt></dl></div> </td> </tr> </tbody></table>
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<tbody><tr> <td align=“center” bgcolor="#fff494" width="25%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap098.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap098.jpg" alt="" border="0" height="106" width="150"></a> </td> <td align=“center” bgcolor="#fff494" width="25%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap103.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap103.jpg" alt="" border="0" height="172" width="150"></a> </td> <td align=“center” bgcolor="#fff494" width="25%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap097.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap097.jpg" alt="" border="0" height="176" width="150"></a> </td> <td rowspan="3" bgcolor="#fff494"> <dl> <dt><font face="verdana" size="-1">The chocolate baby will lack black markings in its feathers - they will be brown. The wing speculum will also appear faded. The colours on this bird will always appear muted or washed out.<br> If you are interested in learning more about the genetics of colour, try our <a href="../Rabbits/RexGenetics.html" target="_top">rabbit colour genetics page</a>, or see the other links at the bottom of this page.</font> </dt></dl> </td> </tr> <tr> <td align=“center” bgcolor="#fff494" width="25%"> </td> <td colspan="2" bgcolor="#fff494"><font face="verdana" size="-1">Above: "Black". Compare this one with the one in the pictures below. </font></td> </tr> <tr> <td align=“center” bgcolor="#fff494" width="20%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05-ap014.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05-ap014.jpg" alt="" border="0" height="108" width="150"></a> </td> <td align=“center” bgcolor="#fff494" width="25%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap015.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap015.jpg" alt="" border="0" height="146" width="150"></a> </td> <td align=“center” bgcolor="#fff494" width="20%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap011.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap011.jpg" alt="" border="0" height="171" width="150"></a> </td> </tr> </tbody></table>
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<tbody> <tr> <td align=“center” bgcolor="#fff494"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap110.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap110.jpg" alt="" border="0" height="155" width="100"></a> </td> <td align=“center” bgcolor="#fff494"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap095.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap095.jpg" alt="" border="0" height="145" width="150"></a> </td> <td align=“center” bgcolor="#fff494"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap106.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap106.jpg" alt="" border="0" height="116" width="150"></a> </td> <td align=“center” bgcolor="#fff494"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap096.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap096.jpg" alt="" border="0" height="129" width="150"></a> </td> </tr> <tr> <td align=“center” bgcolor="#fff494" width="25%"> <font face="verdana" size="-1">Note the difference in the head colouring. The one below is a chocolate - even the colour of the bean is paler than the one above.</font> </td> <td align="center" bgcolor="#fff494" width="25%"> <font face="verdana" size="-1">Of this trio, the chocolate is in the top of the photo.</font> </td> <td align="center" bgcolor="#fff494" width="25%"> <font face="verdana" size="-1">The chocolate here is in the middle.</font> </td> <td align="center" bgcolor="#fff494" width="20%"> <font face="verdana" size="-1">"Black" on left; chocolate on right.</font> </td> </tr> <tr> <td align="center" bgcolor="#fff494" valign="middle" width="25%"><a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:05may-116c.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:05may-116t.jpg" alt="" border="0" height="93" width="160"></a></td> <td colspan="2" align="center" bgcolor="#fff494" valign="middle"><font face="verdana" size="-1">Here we have two 4 week olds (kind enough to stand in exactly the same poses!)- the chocolate is on the left; the black on the right.</font></td> <td align="center" bgcolor="#fff494" valign="middle" width="20%"><a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:05may-114c.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:05may-114t.jpg" alt="" border="0" height="105" width="160"></a></td> </tr> <tr> <td align="center" bgcolor="#fff494" width="25%"> <font face="verdana" size="-1">These pictures show grown up Appleyards. The one in the middle picture is a "chocolate" while the others are "black". The markings are the same, but the middle one has no black on her anywhere, and her wing speculum looks brownish, rather than the beautiful electric blue it is supposed to be.</font> </td> <td align=“center” bgcolor="#fff494" width="25%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-05ap047a.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-05ap047a.jpg" alt="" border="0" height="161" width="150"></a> </td> <td align="center" bgcolor="#fff494" width="25%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-04au077.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-04au077.jpg" alt="" border="0" height="102" width="150"></a> </td> <td align="center" bgcolor="#fff494" width="20%"> <a href="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:sa-04au148.jpg"><img src="lib/exe/fetch.php?w=&h=&cache=cache&media=mhf-photos:t-sa-04au148.jpg" alt="" border="0" height="162" width="150"></a> </td> </tr> </tbody></table>
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farm/colour_genetics.txt · Last modified: by 127.0.0.1