Reptile & Amphibian Forums

From the genetics course work that I took in college it seems to be totally misleading to say that the animals are 66% anything. In a typical Aa x Aa breeding offspring are either AA, Aa, or aa.
Animals that show as the dominate phenotype will be either AA or Aa. Since they show the dominate gene they are either masking a reccessive (Aa) or they are homogeous (AA) period. it is a 50%thing not a 66% possibility. In the overall expected ratio of offspring, 66% of the dominate phenotype could harbor the recessive. On an animal by animal basis it is still just 50%! Am I right?

That's kinda the way I figure it. In a Aa x Aa mating, you would have a 50% probability of heterozygous for the trait denoted by "A" (Aa), a 25% probability of AA (which would not show the normal trait or coloration), and 25% probability of aa. It's kind of a coin toss, though as to which allele either parent is going to contribute to any one offspring, so you can't really apply the results of a Punett calculation strictly to a single clutch. Overall in a series of, say, 100 clutches, that's the percentages you could expect. I'm not exactly sure how they figure that a single snake carries a 66% chance of a particular trait. That might come into play if you are calculating chances of an animal being heterozygous for one or more traits when there are more than one recessive possibility, For instance, if you are talking about a snake that has genes for 3 colors, yellow, black and red. Then a mating of say Ybr x yBR, might produce real numbers like that, but you would just be saying "There's a 66% chance of being heterozygous for one of these traits, not sure which one."

I agree, but there is still only a 50% possibility for each of the genes being carried. The 66% applies to a probability within a given group of individuals as in Out of a clutch of 12 individuals we might expect 25% to be recessive (aa) with 75% of offspring showing the dominate phenotype (the physical apearence)
of these animals there is a probability that around 66% (of just the dominate phenotype) would carry the desired trait as a recessive (Aa) as opposed to 33% that might be AA. However, in any given clutch the ratios may be totally skewed. At best the odds of carrying the recessive gene is still only 50% for the individual. Which, I believe is what most people purchase (an individual).

All of which is subject to other factors including the genes location on the chromosomes. If the trait is near the end of the chromesome it would be easily swapped around in meitosis/Meiosis, or it could be linked (ie extremely close to another gene on the same chromesome) and then would only transfer along with its linked gene or genes. We see examples of linked traits in people with hair and eye color, Dark skin dark eyes, blonde hair blue eyes, red hair green eyes, etc. For a group we see the overall phentypic pattern that emerges, while an individual may have dark skin and blue eyes, or even red hair and brown eyes.

There now I've made everything confusing again

Bob

Nope, not confusing at all...what you are saying agrees with everything I know. And to make matters worse, because the Aa offspring will have normal coloration, you don't know if it's heterozygous for sure until you breed it with an animal that is AA to see if a percentage of that offspring is AA, and then depending on clutch size, etc., you may still not know until subsequent breedings occur. You could also breed with a known Aa animal, but the percentages of AA offspring are smaller.

May I inject some moron?
so if you breed a k-snake 5050 with a albino -would you get
a 100% chance that the animals will all 5050's? -normal looking animals?
and if you breed two 5050's that look the same ,would you have a 25-30% chance of albinism? and the rest would be 5050's -normal looking animals?
Please if one of you have time, please explain in detail ,I’m confused ,and also could you recommend a book on this subject?
there are so many , I’m not sure which one to buy ......thanks ,
Dallas Wiebelhaus.
and HEY! oldherper.......what's up brother? what do you think?

Hey Mr. Dwiebelhaus..I'm fine. Here's what I think..

May I inject some moron?

Sure, if you find a moron, you can inject him/her all you want.

so if you breed a k-snake 5050 with a albino -would you get
a 100% chance that the animals will all 5050's? -normal looking animals?

This is going to depend on the genetic makeup of the 50/50. Each snake carries two genes for each color. Each parent will contribute ONE gene for that color to each offspring. So, if you have an albino, the genetic makeup is said to be AA, the capital "A" meaning that gene is incapable of producing the pigment for that color, so that's the "albino gene", if you are talking about black pigment. The lower case "a" means the gene will produce normal coloration, or normal amounts of that particular pigment. If a snake has received one of each type of gene from it's parents, it is said to be heterozygous (different zygotes). In this case, each of the "types" of genes, A or a, is called an allele. In the case of a Corn Snake, there are genes for 3 different pigments, red, black and yellow. If a snake is known to be heterozygous for 2 of these colors, then he is said to be "double heterozygous". Which one of the alleles the parent contributes is a matter of chance. You can use what's called a Punnett Square to predict the possible outcomes, but it's not going to necessarily be accurate for any one particular clutch because of the random nature of the contributions. It's sort of like predicting coin-tosses. You know you have a 50/50 chance of getting 'heads", but there's the possibilty of getting "heads 3 or 4 times in a row.

At any rate, if a snake possesses one gene that will produce normal coloration, it will be normally colored. For a snake to be albino, BOTH genes have to be "A".

and if you breed two 5050's that look the same ,would you have a 25-30% chance of albinism? and the rest would be 5050's -normal looking animals?

Once again, that's going to depend on the genetic makeup of the animals. If they are both "aa", then there is a zero chance of producing albino offspring. There are recessive genes present in all populations, so there is a small chance that one of the parents would have the Aa gene structure and and even smaller chance that two of them would, under natural conditions, get together and mate. This is the scenario that would possibly produce albinos in the wild. Since albinos have a very small cahnce for survival in the wild because of a lack of natural camouflage, they are not likely to reproduce and produce a higher percentage of AA animals.

Please if one of you have time, please explain in detail ,I’m confused ,and also could you recommend a book on this subject?
there are so many , I’m not sure which one to buy ......thanks ,
Dallas Wiebelhaus.
and HEY! oldherper.......what's up brother? what do you think?

As far as books, some of the old works of H. Berndt Bechtel (difficult to find now) and Kathy Love are pretty good regarding this subject.

Hope that helps a little...if you have more questions, just ask. If I can't answer them, I'm sure someone can.

so if you breed a k-snake 5050 with a albino -would you get
a 100% chance that the animals will all 5050's? -normal looking animals?

First of all, I assume you mean 50% prob of being heterozygous albinism (what else is a 5050 supposed to be?).

If you breed a snake with a 0.5 (50%) prob of being a heterozygote to an albino, you have a 25% chance of albinism in the offspring. This is calculated by multiplying the probability of producing an albino from a het x albino cross (0.5) by the probability that the original snake is heterozygous to begin with (0.5).

If you mean a 50% black 50% white animal, then you are breeding a normal snake to an albino and will produce 100% heterozygous snakes. How much black or white they will have is controlled by a different series of genes and isn't inherited as a simple dominant/recessive trait.

and if you breed two 5050's that look the same ,would you have a 25-30% chance of albinism? and the rest would be 5050's -normal looking animals?

If, again, you are implying a 5050 has a 50% chance of being heterozygous for albinism, then mating two of your 5050 snakes would have a 0.0625 (6.25%) probability of producing an albino in the offspring.

Again, you multiply the probability of producing an albino from the parents if they are both heterozygous (0.25) by the probability that parent 1 is a het (0.5) and the prob that parent B is a het (0.5) so you get 0.25 x 0.5 x 0.5 = 0.0625.
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Chris Harrison

My assumption was that he was talking about what's commonly called a 50/50 Cal King...50% white and 50% black. In that case, IF one of them HAPPENS to be het, then a and A genes would be passed to SOME of the offspring. The point that I was getting across on this question was that the coloration of the parent is no indicator unless it is an albino.

Hi,
It's actually pretty simple... it happens when you breed a snake that is homozygous for a recessive trait (aa) to a snake that is heterozygous (Aa). 25% of the offspring will be homozygous for the trait (aa), 50% will be het (Aa), and 25% will be "normal" (AA). Only the homozygous (aa) animals can be visually distinguished from the rest of the clutch, the hets and normals will both look alike. Since you have 50% hets and 25% normals, the chances are that 2/3 of them (66%) will be hets.

Nate

Hi Nate,
You said that "Since you have 50% hets and 25% normals, the chances are that 2/3 of them (66%) will be hets."

That is true for the clutch, but not the individual. The individual has a 50% chance of having the recessive gene. As oldherper said it's a coin toss.

Bob

I don't understand what you are trying to say. 50% over 25% is 2:1. Or in other words 66%. The reason we say 66% poss. is because we know that it is not homozygous for the recessive. Therefore it can only be het or homo forthe dominant. The chances that an individual is going to end up with the gene is not 50% it's 75%. (Aa x aa) Three out of four alleles is a, 75%. The chances that an individual (that doesn't show the recessive phenotype) carries the recessive gene is 66%.
Obviously these "rules" are almost useless but can give you an idea if something is possible at all. I mean technically there is a 50% chance that the sun will rise tomorrow morning. It either eill or it won't. But on the other hand...I'd be willing to bet every penny I had on the sun coming up in the morning.
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International Snakes Meetup

For arguement sake we will deal with one set of genes
where A= recessive gene for albinism and a= dominate "normal"

(I don't understand what you are trying to say. 50% over 25% is 2:1. Or in other words 66%. The reason we say 66% poss. is because we know that it is not homozygous for the recessive. Therefore it can only be het or homo forthe dominant. The chances that an individual is going to end up with the gene is not 50% it's 75%. (Aa x aa) )

For starters we are talking about two seperate issues:
Genotype (the genetic makeup of an individual)
Phenotype (the physical apearence of an individual)

Genotype is either Aa or aa for an individual. We all agree that the animal is normal color ie has at least 1 "a" gene and that the other gene the animal has could be "A" or "a". An individual cannot have a greater chance then that.

You have arbitrarily eliminated the obvious albinos or AA. By eliminating one fourth of your sample group you have arrived at an erroneous conclussion as to the probability on an individual to possess the desired trait.

(Three out of four alleles is a, 75%. The chances that an individual (that doesn't show the recessive phenotype) carries the recessive gene is 66%. )

Phenotype cannot be recessive. Phenotype is the outward physical apearence. In this case a normal looking snake. The genotype or genetic makeup has only two possibilities one parent obviously contributed an "a" gene the other parentcan only give an "A" or "a". Genotype for the individual is 50%.

(Obviously these "rules" are almost useless but can give you an idea if something is possible at all. I mean technically there is a 50% chance that the sun will rise tomorrow morning. )

Until there is evidence to show that in the past the sun has not risen, the probability that it will rise tomorrow is 100%.

(It either eill or it won't.)

No it must be assumed that it will, because there is no evidence to show that it won't.

(But on the other hand...I'd be willing to bet every penny I had on the sun coming up in the morning.)

Almost everyone would bet that the sun will come up tomorrow.

If we were buying animals for just the phenotype it doesn't matter either way. The bottom line is that people are usually buying for a genotype and not the phenotype. In that situation the correct statement is a 50% chance.

Bob Bull

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You are looking at this from two perspectives at once.

You are correct that for a normal looking snake, there are only two possible genotypic outcomes (AA or Aa), but the probability of each outcome is not the same. This is why it isn't a 50% probability.

The 66% thing is an answer to the question "What is the probability that this snake is heterozygous?"

The answer is 66% because two thirds of the dominant phenotye snakes will be hets. Therefore the probability that any one individual with the dominant phenotype will be heterozygous is 2 chances out of 3 (regardless of how many offspring there are).
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Chris Harrison

Alright great ,I’m going to have to look in to this more, it's
very interesting weather your going to breed or not.
may I ask a question that may be a little taboo or just a matter
of opinion?
if you have two parents that have breed ,producing 1 male and 1 female offspring that have the desirable traits to produce an
animal that you want ,in other words - "inbreed" two siblings to produce an
desired effect ,can this be considered? since it's certainly
probable in the wild? -

People do it all the time. It can result in physical abnormalties, though.

I dunno...I think it's just less misleading to say "possible het". If you pick any one snake out of a clutch from this type of mating that has normal coloration you can say there's a 66% chance that this snake is het. But you can also say, that it either is or it isn't, so it's 50-50 for that one individual. Or, it could be looked at as "if this snake has 2/3 possibility, and this one has 2/3 possibility, then this one must have 1/3 possibility (just kidding about that one).

The bottom line is, that if you are planning to breed for a particular genetic trait, you need to buy at least 2.4 possible het animals to breed, and preferably some that are homozygous for that trait.

It would be possible to have a 50% possible het, if you bred a het to a normal. I don't think there's anything misleading about using probability percentages to describe possible het. animals, since the percentages describe the animals as accurately as possible, and give you a bit of information about the genetic makeup of the parents.

Nate

:I dunno...I think it's just less misleading to say "possible het". If you pick any one snake out of a clutch from this type of mating that has normal coloration you can say there's a 66% chance that this snake is het. But you can also say, that it either is or it isn't, so it's 50-50 for that one individual. Or, it could be looked at as "if this snake has 2/3 possibility, and this one has 2/3 possibility, then this one must have 1/3 possibility (just kidding about that one).

Let's say I put three cards face down on the table. Two are aces and one is a deuce. If you pick one, there is a 66% chance that you will pick an ace. Any given card either is or is not an ace, but when you go to pick one, two out of the three cards are still aces. IOW, the odds of getting an ace are still 66%.

You can also say that every lottery ticket either is or is not a jackpot winner. So why haven't I won a few million bucks yet? 8-)

Paul Hollander

You said"Let's say I put three cards face down on the table. Two are aces and one is a deuce. If you pick one, there is a 66% chance that you will pick an ace. Any given card either is or is not an ace, but when you go to pick one, two out of the three cards are still aces. IOW, the odds of getting an ace are still 66%. " And you said "If you pick any one snake out of a clutch from this type of mating that has normal coloration you can say there's a 66% chance that this snake is het."

Yes, for the cards that have one demension (phenotype only) that is a correct statement. If you say 2/3 of the normal phenotype could be het for albino it is a true statement, but for each snake (the individual genotype) it is a 50% chance that the unknown gene is recessive. It can't be anymore for the individual.

Bob