Multiple Alleles (2024)

It makes absolutely no sensewhatsoever to continue if we don't know what the word "allele" means.

For example, in Mendel's peainvestigations, he found that there was a gene that determined the colorof the pea pod. One form of it (one allele) creates yellow pods,& the other form (allele) creates green pods.

Get it? Two possible phenotypes of onetrait (pod color) are determined by two alleles (forms) of the one "color"gene.

When the gene for one trait exists asonly two alleles & the alleles play according to Mendel's Law of Dominance,there are 3 possible genotypes (combination of alleles) & 2 possiblephenotypes (the dominant one or the recessive one).

Using the pea pod trait as anexample, the possibilities are like so:

GENOTYPES hom*ozygous Dominant (YY) Heterozygous (Yy) hom*ozygous Recessive (yy)	RESULTING PHENOTYPE Yellow Yellow Green
where Y = the dominant allele for yellow & y = the recessive allele for green

If there are only two alleles involvedin determining the phenotype of a certain trait, but there are threepossible phenotypes, then the inheritance of the trait illustrates eitherincomplete dominance or codominance.

In these situations a heterozygous(hybrid) genotype produces a 3rd phenotype that is either a blend of theother two phenotypes (incomplete dominance) or a mixing of the other phenotypeswith both appearing at the same time (codominance).

Here's an example with Incomplete Dominance:

GENOTYPES BB = hom*ozygous Black BW = Heterozygous WW = hom*ozygous White	RESULTING PHENOTYPE Black Fur Grey Fur White Fur
where B = allele for black & W = allele for white

And here's an example with Codominance:

GENOTYPES BB = hom*ozygous Black BW = Heterozygous WW = hom*ozygous White	RESULTING PHENOTYPE Black Fur Black & White Fur White Fur
where B = allele for black & W = allele for white

Now, if there are 4or more possible phenotypes for a particular trait, then more than 2 allelesfor that trait must exist in the population. We call this "MULTIPLEALLELES".

Let me stress something. Theremay be multiple alleles within the population, but individuals have onlytwo of those alleles.

Why?

Because individuals have only two biologicalparents. We inherit half of our genes (alleles) from ma, & theother half from pa, so we end up with two alleles for every trait in ourphenotype.

There are 3 alleles for the gene thatdetermines blood type.
(Remember: You have just2 of the 3 in your genotype --- 1 from mom & 1 from dad).

The alleles are as follows:

Notice that, according to the symbolsused in the table above, that the allele for "O" (i) is recessive to thealleles for "A" & "B".

With three alleles we have a higher numberof possible combinations in creating a genotype.

Notes:

• As you can count, there are 6 differentgenotypes & 4 different phenotypes for blood type.
• Note that there are two genotypes for both"A" & "B" blood --- either hom*ozygous (I^AI^A orI^BI^B) or heterozygous with one recessive allele for"O" (I^Ai or I^Bi).
• Note too that the only genotype for "O"blood is hom*ozygous recessive (ii).
• And lastly, what's the deal with "AB" blood?What is this an example of? The "A" trait & the "B" trait appeartogetherin the phenotype. Think think think .... {ANSWER}

Let me inform you that in my time teachingthis fabulous subject of biology & this incredibly fun unit on genetics,the only multiple allele questions I have ever seen have been about thehuman blood type trait. So included here, for your academic pleasure,are some examples of these types of questions. Work out the problemson paper & then click to see the solutions.

(Irealize that paper is old-fashioned in the world o' internet, but I
haven'tbecome technically savvy enough to do it any other way .... yet.)

1. A woman with Type O blood anda man who is Type AB have are expecting a child. What are the possibleblood types of the kid? {answer}

2. What are the possible blood typesof a child who's parents are both heterozygous for "B" blood type?{answer}

3. What are the chances of a woman withType AB and a man with Type A having a child with Type O? {answer}

4. Determine the possible genotypes &phenotypes with respect to blood type for a couple who's blood typesare hom*ozygous A & heterozygous B. {answer}

5. Jill is blood Type O. She hastwo older brothers (who tease her like crazy) with blood types A &B. What are the genotypes of her parents with respect to this trait?{answer}

6. A test was done to determine the biologicalfather of a child. The child's blood Type is A and the mother's isB. Dude #1 has a blood type of O, & dude #2 has blood type AB.Which dude is the biological father? {answer}

Well, that's all I have tosay about that .... hope it was helpful.