Chicken Genetics

the lab that we're about to work on today is primarily involved with Mendelian genetics and the examples used in the lab deal primarily with poultry and for that reason we're basically going to look at a number of the examples with our hands on the chickens themselves and to look at some of the eggs so we got a better feel for the traits that we're working with and the traits that you'll be dealing with on your homework sets today to help me with my example is dr. George Brandt who's a professor in animal science and these are some of his birds and some of the eggs from the poultry farm that he's involved with they all come from the Iowa State poultry farm that's near campus we're going to be dealing with primarily four traits today the first trait is eight color and we'll be showing some examples about that and discussing the inheritance pattern the second is plumage color which involves incomplete dominance and provides a very good example for that the third trait is a type of comb and we'll show you three examples from there and the final deals with rate of feathering and how it relates to sexing of chickens first example for a color that we're going to discuss deals with blue and white eggs and the inheritance pattern for them is rather simple blue is dominant to white and as you can see an animal which may be either homozygous for the blue allele or heterozygous for the blue allele will produce blue eggs white is recessive to blue and an animal hen has to be white has to have the genes for white eggs - in fact produce the white egg so she has to be homozygous for the little o allele and that will produce white eggs now let's take a look at some of these eggs so we have a feel for the different colors that we're talking about the first one that we're going to show you and is in front of dr. brandt here is a common right egg very common we all see those in the supermarket the next egg and the one we've been dealing with in terms this genetics problem is a blue egg and as you can see there's a great deal of variation amongst the color blue here perhaps dr. Brandt you'd like to tell us a little bit about the chickens that he's come from the white eggs are from the most common type of egg layers in the United States which is a white Lagan the blue and green shades of eggs come from a rather recent import from South America called the Araucana it's very popular because of its novelty now we also have here in front of me are some brown eggs and brown eggs aren't seen very commonly in the United States but of course they're common in many parts of the world what type of bird - these come from well there are variety of birds which lay brown shelled eggs for instance a meat type birds lay brown shelled eggs but for egg production Plymouth Rock New Hampshire and Rhode Island Reds are most common now we're not going to deal with this example today but it's at least interesting to see that there are variety of colors of eggs to deal with the example that we're most interested in again are the blue and white eggs and I here have here another tray of them as you can see there are three blues a very similar color to other blues which are somewhat different this is caused by modifying genes and here we have the white the five white eggs again the inheritance pattern is is very simple white is recessive to blue the hand is homozygous for the white alleles the recessive alleles the eggs will be white she's either heterozygous or homozygous for the dominant allele associated with the color blue then her eggs will be blue the next example that we're going to deal with deals with incomplete dominance we've already discussed incomplete dominance as it relates to coat color and Cattle I hope you'll remember from the lecture we discussed cattle that the coat colors were white roan and red and we have a similar example with chickens that we're going to show you today even though it's not in the lab book for the first laboratory this example of incomplete dominance deals with three colors white or splashed white as it's called blue and black white is homozygous for the little B allele blue is heterozygous for the Big B little B alleles and black is homozygous for the Big B allele if we cross chickens which are Big B little B by Big B little B or in other words we cross two birds that are blue we would expect to get offspring whose colors are black blue and white in the frequencies one black to blue and one white dr. Brandt and I are holding the three chickens and they all represent the three colors we talked about the first bird is obviously a black when the dr. brandt is holding on and that's homozygous for the Big B allele the second bird that he has here is a splash white bird not completely white but spliced white and the white bird is homozygous for the little B allele and the bird that I'm holding here is considered to be blue and this bird basically is heterozygous a Big B little B crêpes dr. brand like to say a little bit about these birds and where they come from this breed is the blue Andalusian breed which comes from the Mediterranean area it's related to the Reagan breeds and lays large white eggs as we saw earlier so again let's review once more the color combinations that we have we have black homozygous for the Big B allele homeless splash white which is homozygous for the little B allele and the heterozygous animals showing the incomplete the dominance is blue and this one is Big B little B is its genotype this next example deals with comb type this example differs from the others that we discussed before because it deals with an example of a trait that's controlled by genes at too low sy and those that we're going to look at our different combs and we'll look at three of the four examples that we talked about in the lab manual walnut comb will not be included but it's an animal which is which contains the dominant alleles at both the R and the P locus so an animal that has one large R or a large p allele as both of them will produce in a walnut comb a rose comb individual is an animal that is homozygous for the recessive small P allele and can either be heterozygous or homozygous for the large R allele the third comb type and we have an example of that also is a P column and this is an animal that is homozygous for the recessive little R allele and either can be heterozygous or homozygous for the capital P allele and the final comb type which we also have an example for it's the single comb and this is an animal that is homozygous at both low side it has little R little R and little P little P we just looked at for examples of comb types and here we have three birds we do not have a walnut comb and I'll come back to that in a few minutes to discuss what a walnut comb might look like but let's start first with the bird that dr. Brandt is holding and this is a bird that has a single cone dr. brand perhaps you'd like to discuss this bird well this is an orphan ttan the single comb is the most common comb type that we have you'll notice that it's a narrow blade of tissue with points along the top and a longer what's termed blade at the back of the bird's head now many breeds that are common in the u.s. they used to be common or in some of the commercial stocks have the single comb is that correct the leg horns and the Plymouth Rocks and the Rhode Island right that's correct okay and now the second bird perhaps you'd like to tell us about that comb type well the second bird is a Wyandotte and it has a rose comb you'll notice that the comb is rather broad and flattened it has some bumps and nodules on it and at the very back it has a very long what's termed spike which lays along the back of the bird's head okay and the third comb type that we talked about is the pea comb yes this is found in the corniche you'll notice that it looks somewhat like three small single combs lined up side-by-side the corniche is a bird which was used extensively in the breeding for our broilers because of its very heavy muscle I see now the walnut comb which we don't have an example for is usually produced of course by crossing of some of the other types but of crossing basically the the pea and the rose type will produce a walnut comb it's one way to get it now a walnut comb would have just a little bit of comb down here at the end and it looked like a piece of a shell the walnut is that correct yes let's review something about what we've talked about about comb types we've had three examples of the four we've discussed comb type is controlled by genes a tool to low sigh we have the big R allele and when that is combined with the big P allele we have a walnut comb which we don't have an example for the Rose comb results from a homozygous little P alleles and a big R allele for the our locus P combs Reba come from the very fact that we have homozygous small R those are the recessive alleles and we have a large p allele to produce the P comb and finally the single comb which we looked at first is a result of homozygous recessive at both the R and the P locus our last chicken example deals with sex-linked traits and we'll be looking at two traits rate of feathering and borrowing in the chicken the homogamy DEQ's x is the male and the female is the hetero comedic sex sex and that's just the opposite of what situation we have with in fact in humans now let's first look at slow feathering and rapid feathering for the male since it's the homo comedic sex it needs the dominant K allele it doesn't make any difference what the other allele is and it will be slow feathering the female on the other hand will show the allele that she is if it's Big K she'll be slow feathering if it's little K she'll be rapid feathering little K is recessive too big case a rapid feathering is recessive so the only way that a male will be rapid feathering is to be little k little k a similar example exists for barring where a Big B will produce a barred animal whether it be in the mail or in the female little B will produce no bar if it's alone of course it will be in the female but it has to be homozygous little B little B to produce no bar in the male the two traits that we've talked about rate of feathering and borrowing can be used therefore to sex chickens and this is very useful at the day of hatch rate of feathering is commonly used in the egg-laying varieties and barring may be used in some of the meat production lines but it's also used in some of the varieties use for show now let's take a look at the chicks that dr. Brandt and I have these were kindly provided for us by Highline poultry which is in Dallas Center Iowa and we have each have two birds and two males and two females and what we're going to demonstrate then is the rate of feathering and we'll show you the differences so you have a good feel for how these might be used to sex the the chickens at the day of hatch or the day after for that matter the birds that I'm holding are in fact females and they are rapid feathering and I'll hold up a wing here of one of the birds and now dr. Brandt will show you the wing feathers on one of his two birds and this is a slow feathering and this is used to denote the male if you look very closely you will notice that every other feather in the rapid feathering a bird here which is the female is short and every other one is long if we look however at the male birds the dr. Brandt has and we look at one of the examples here every one of the feathers is approximately the same length now we don't have an example of borrowing but this example of rapid and slow feathering is quite useful to show you something about a sex-linked trait and how it might be used to sex chickens at birth let's review the traits that we've covered today we've talked about egg color we looked at blue and white eggs blue being dominant to white color we've also talked about plumage color another trait that at least for this example was controlled by a single set of alleles at one locus and we had black white and blue animals and this is an example of incomplete dominance we looked at comb type a trait that was controlled by genes at too low Tsai and you remember we talked about four types of combs walnut P Rose and single combs and finally we talked about two sex-linked traits rate of feathering and borrowing and we looked at an example of rate of feathering and discussed how that might be used for sexing of chicks a day of hatch let me again thank my colleague dr. Brandt and let me thank a hiline of poultry in dallas center for providing us with some of the birds that we use for today's example