Mission 1: Parakeet Caper

MISSION NAME: Parakeet Caper

STATUS:

LOCATION: Perth, Australia

DIFFICULTY RATING: 25% (Training Mission)

TERMS TO KNOW:

gene:

a unit of hereditary information consisting of DNA (the instructions for the genetic composition of living organisms).

trait: a characteristic of an organism.

genotype: the symbolic representation of a trait.

monohybrid cross:

a breeding experiment that maps out all possible varieties of a single trait in the offspring of two known parents.

dihybrid cross:

a breeding experiment that maps out all possible varieties of two traits in the offspring of two known parents.

punnet square:

a tool designed to perform crosses between genes, and to return the resulting genotypes of the offspring.

BRIEFING:

Hello . Like all GMF rookies, you are going to start off with a training mission so that you can learn the basics of genetics and get a feel for what the missions are like. For this mission, you have been assigned a partner, Seymore. He's along to make sure everything goes well and to help you if you need assistance If you ever have any questions, just click on the "Ask Seymore" image in the toolbar and he'll give you a special hint depending on where you are in the mission.

Your first mission will take you to Perth, a city in southwest Australia. This year's city fair featured a parakeet breeding contest sponsored by a local pet store owned by a guy named Jack. Each contestant was to breed the best-looking parakeet possible using a blue parakeet and a green parakeet as the parents. Jack would then judge the offspring, and the winner would receive the best-of-show award. There is a problem, the most popular bird in the show is different from all the rest, and Jack , the contest judge, thinks that this entry isn't the offspring of the required parents. What you need to do is determine if this bird is in fact a fraud, or if it is a legitimate result of the breeding of the two parents.

Here's a little background info to help you get started:

Basically, every characteristic of an organism (eye color, blood type, etc.) is controlled by genes on that organism's chromosome(s). Each gene is made up of two parts called alleles (pronounced "uh-leel"). The alleles can be dominant or recessive. For example, the color of the outer layer of a parakeet's feathers is controlled by a gene. This gene is made up of two different alleles. The allele for yellow color is dominant, and the allele for a colorless condition is recessive. To keep track of these traits, geneticists make a symbol for each allele. The symbols are usually the first letter of the trait, and the symbol is capitalized if it is a dominant allele, and lowercase if it represents a recessive allele. The dominant allele for yellow feather color is symbolized with 'Y', and the recessive allele is symbolized with 'y' for a colorless condition.

Because genes are made up of a pair of alleles, many different combinations of alleles are possible. The gene symbolized 'YY' would result in yellow feathers, and the gene 'yy' would result in white, colorless, feathers. These genes are called homozygous for that particular trait because they are made up of two of the same alleles. Another possible combination is 'Yy' which is heterozygous (has two different alleles for the trait). The combination 'Yy' would also result in yellow feathers because the allele 'Y' is dominant to the allele 'y', causing the color to occur.


YY or Yy	yy

When you breed two organisms, the alleles from each parent split up and combine with alleles from the other parent to form new genes that control the characteristics of the offspring. To figure out all the possibilities for the offspring, geneticists use what is known as a punnet square to map out the breeding process. When geneticists want to track a particular trait as it is passed on through the generations, they perform a monohybrid, or one-trait cross, using the punnet square. A mono hybrid cross would look like this...

As illustrated in the chart above, each parent contributes one of the two alleles needed for the offspring's color trait. Because the parents each contributed one allele, the F1 generation has one allele from each set, causing it to be heterozygous. The F1 generation then contributes its alleles to the next generation, but since there are two different alleles, there must be two different options that need to be considered. This is why there are two different alleles represented in the punnet square. These alleles then combine to form the actual offspring (F2 generation).

The above monohybrid cross illustrates the mapping process for one trait, but what if you want to consider two traits at once? What you need to do is use a dihybrid cross. The dihybrid cross is just like the monohybrid cross, only there are twice as many alleles because there are two traits instead of one. This can be illustrated using parakeets again because the total feather color of a parakeet depends on two genes - one for the yellow color as above, and one that determines if a pigment, called melanin, will exist in the feather core. The following images show how this affects the feather color:

The blue color of the melanin (symbolized with B), when combined with the yellow pigment, will make a green-feathered bird, and the melanin alone will cause the feathers to be blue. Thus, the genetic symbols for these feathers would be:

YYBB or YyBb
yyBB or yyBb
YYbb or Yybb
yybb

Each parent would contribute two alleles (one for color, the other for melanin) when creating the gametes. If you had homozygous parents YYBB and yybb would produce the gametes YB and yb which would result in an F1 generation of YyBb. Since there are four different alleles in the F1 generation, there will have to be four different gametes for the F2 generation - YB, Yb, yB, and yb. these would be assembled on the punnet square like this:

	YB	Yb	yB	yb
YB
Yb
yB
yb

When you calculate the punnet square, your offspring will have four alleles, and will represent a feather color as listed in the chart above. In this first training mission, you will be dealing with the feather color of a parakeet, and you will need to perform a dihybrid cross to map out the offspring. For your convenience, the GMF has provided the Punnet Calculator as a standard tool while you go through the missions. To use it, you will need to figure out the gametes as shown in the above punnet square, input these gametes into the text fields on the calculator, and press the calculate button. The resulting F2 offspring will show up in the empty spaces.

Your mission, should you choose to accept it, is to calculate all the possible offspring from the two parakeet parents mentioned in the second paragraph, and determine if the bird in question is a possible result from the crossing of the two parents. When you click accept, you will be transported to Jack's Pet Shop where you can talk with Jack and find out information on the parakeets. When you find enough information to calculate the crosses, click the solve button to submit your results.