I do not get this at all can someone please explain it to me please? I'm not asking anyone to do the questions just how to do each one, I missed the lesson that day. Thank you:) Medel's law of dominance and segration are to be used 1.A In the summer squash, white fruit colour is dominant; yellow is recessive. If a squash plant is homozygous for white is crossed with a homozygous yellow, predict the appearance of the F1 generation and the F2 generation. 1.B If an F1 is crossed with a homozygous white indicate the possible offspring 2.A In humans brown eyes are dominant and blue eyes are recessive. Make a Punnett square showing the possible eye colours of the children of a heterozygous, brown-eyed father and a blue-eyed mother. Give the phenotypes and genotypes ratios of the children. 2.B Two browned eyed parents have two children with blue eyes. Give the genotypes of wasch member of the family. 3. The polled (hornless) trait in cattle is dominant ; the horned trait is recessive. Certain polled bull is mated to three cows. Cow A, which is horned, gives birth to polled calf. Cow B, also horned, produced a horned calf. Cow C, which is polled, produced a horned calf. What are the genotypes of the four parents? 4. In sheep white coat is dominant, black is recessive. Occasionally a black sheep appears in the flock. How could the farmer eliminate the gene for black from his flock? 5. Why would offspring of families with a history of diabetes mellitus ( a recessive trait on both the mother's and father's side be more likely to develop the disease than offspring of families in which diabetes has occured only on one parent's side of family? Use Punnett squares in your explanation 6.An extra finger in man is rare, but due to a dominant gene. WHen one parent is normal and the other parent has an extra finger, but is heterozygous for the condition what is the probability that their first child will be normal? their second? their third? 7. Albinisn (lack of pigment) in man is caused by a recessive gene. If normal parents have an albino child, what is the probability that their next child will be normal colour? 8. Outline a possible cross to determine whether a black guinea pig is homozygous or heterozygous for the colour trait. This called a test cross, A test cross is method used to determine whether an organism that shows a dominant is pure dominant whether it is heterozygous 9. Suppose you were a cat fancier and were raising what you thought was a purebred but some of the cats had spots of white hair at their tips of their tails, while did not. How could you determine whether this trait is recessive or dominant? that only one pair of genes is affecting this trait.
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Important definitions: dominant gene - if it is there, its phenotype (ie. eyes being brown instead of blue) will be expressed recessive gene - its phenotype will only be expressed if there is no dominant gene (remember, each person has 2 copies of the same genes, 1 from your dad, 1 from your mom) homozygous - both copies of the genes are the same (ie. both your parents gave you the gene for brown eyes) heterozygous - the two copies of that gene are different (ie. one parents gave you gene for brown eyes, one parent gave you gene for blue eyes) F1 - first generation F2 - 2nd generation 1A. I usually do these questions using a Punnett square, although something this simple you'll soon memorize the pattern. To make Punnett square: 1) Make a 2x2 table 2) Take the genotype of one parent and use each gene to label a column. So in this example, we know one parent has homozygous white. That means its genotype is white white. So label both columns as "white". Usually people choose a letter to represent the gene, and capitalized == dominant, not capitalized == recessive. So let's call white W. Then you should label the 2 columns as W. 3) Take genotype of the other parent and use each gene to label a row. In this example, the other parent is homozygous for yellow - ww - so label each row with a 'w'. 4) Go through each square and fill in the labels of the columns and row it occupies. And there you have the genotype for your F1 progeny. It should be 100% Ww 5) Phenotype is what they'll look like. As mentioned above, dominant traits are always expressed, so in this case, W (ie. white) is expressed. Now take two of the Ww and use them as the new "parents" in a Punnett square to find the genotype/phenotype of the F2 kids. So you should have 1 column called "W", the other column called "w". Similarly, one row called "W", one row called "w". You should end up with a percentage of white kids, and a percentage of yellow kids. 1B. Make a punnett square with Ww and WW 2A. Make a Punnet square. Father they told you is heterozygous. They didn't say anything about the mom because if she is displaying the recessive trait (ie. blue eyes), she is obviously homozygous recessive. 2B. Genotype of kids are easy, they are showing recessive traits (see 2A). Genotype of parents.... if we know the kids have 2 blue genes, that means they got one from each parent. What genotype do the parents have to have to be able to give blue gene and show brown trait? 3. You are able to get kids with recessive traits from a bull showing dominant trait. What genotype is the bull? (see 2B) CowA (see 2A) CowB (see 2A) CowC (same reasoning as the bull) 4. This one I'm not 100% sure, but here's my take on it. Breeding is how you pass on genes. Don't breed = don't pass on genes. Works for any gene (I think). Recessive means sometimes breeding dominant sheeps would still give recessive kids... but if you keep stopping black sheeps from breeding, eventually hopefully it'll work. Another part of this anwer might be that you can never be sure you wiped out black sheeps.. because even when you have all white sheeps, there's a chance some of them are heterozygous, and by "luck of the draw", never pass on the black gene at same time as its partner. Dominant genes, on the other hand, will always be wiped out if you wipe out dominant displaying sheeps. That's why lethal genetic diseases are usually recessive traits. 5. Mmm, not sure why you need a Punnett square to answer this. But maybe make a Punnett square showing that if someone had diabetes, all of his/her kids would at least carry the gene for it? Compared with a Punnett square of someone who is not showing diabetes, then the kids may or may not be carrying the gene. That means, if these "kids" are actually your parents, then in case1, your parents will always be a carrier. In case2, you parents may or may not be carriers. 6. Do a Punnett square. This gives you the probability. Then realize that the same probability holds true for each child. Just like flipping a coin. Everytime you flip, it's 50/50. Because you got heads last time doesn't make the next flip not 50/50. 7. See 6 If you need help with parent's genotype to begin with, see 2B 8. It's asking you what you should breed your guinea pig with to find out if it's homozygous or heterozygous. Your choices are find a guinea pig that is: homozygous dominant, homozygous recessive, heterozygous. Think about what kind of kids you'll get for each combination and in what percentage. Since this is pretty common and many teachers give out the answer in class, I'll tell you the answer at the end of this post. 9. I'm not 100% sure on this one. I'd say breed a cat with white tip with a cat without white tip. The kind of offsprings you get more of is dominant. As for one pair of gene or not. Not sure if this is what they're getting at, but most traits that are affected by more than one gene tends to have a gradient. Like maybe some spots are grey, instead of just black or white? Look at my wiki source for more information. Most people would use an animal with recessive traits. That way you have a higher chance of seeing the recessive trait if it occurs. And if it does occur, you know your original dominant guinea pig HAS to be heterozygous.
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