Genetic Problems I: The center for the study of hobbits...

Genetic Problems I: The center for the study of hobbits located in Hobbiton obtained the following results using knobby knee and normal knee hobbits of unknown genotypes. Here is the result of the study group phenotype: Cross Parents Offspring Female Male Knobby Normal I Knobby Normal 82 78 II Knobby Knobby 118 39 III Normal Normal 0 50 IV Knobby Normal 74 0 V Knobby Knobby 90 0 Consider both knobby parents in cross V are homozygous. Use N for dominant and n for recessive allele. Based on data provided; 1) What are the genotypes of parents in each cross? You must draw the punnett square for each cross and show your work. (4 points) 2) What is the type of Inheritance? (1 points)> 3) If the knobby knee female in cross I were mated with the knobby male in cross V, what is the genotypes ratio for offspring? Draw punnett square. (2points)

Transcript

00:01 We have multiple different groupings here where we are told phenotypes and we want to determine genotypes.

00:05 So we're going to look at a few of them here.

00:07 We're starting with one of them where we're told that one parent has knobby knees and one parent has normal knees.

00:16 And we end up with 50 % of the offspring that have knobby knees like the first parent and the other 50 % have normal knees like the second parent.

00:27 Well, we don't really know too much from that.

00:31 So we're going to move on to the next one where we're told that both parents have knobby knees, and then 75 % of the offspring have knobby knees, and the other 25 % have normal.

00:47 Now, this one tells us a lot, because if you have two parents that have the same phenotype, but then their children, there's two different options for their phenotype, they could be like their parents or they could be something else, then we know that what the parents have is the dominant trait.

01:07 Because if it were not, if the parents had the recessive trait of being knobby need, then that would mean they would have to have only recessive alleles, which means they could only pass on recessive alleles, and there's no way they could have a dominant type offspring.

01:24 So this tells us that the parents ' phenotype, which can be passed on to the children, or the children could have the other one, what the parents have is dominant.

01:34 So parents who have knobby knees have to have at least one dominant allele, and the offspring who have nominally have to have at least one dominant allele.

01:43 Now, if they are able to have children who have the recessive phenotype, that means those children can only have recessive alleles.

01:52 So they have this genotype.

01:55 Well, if they have two recessive alleles, that means they had to get one from one parent and one from the other parent.

02:01 So we are dealing with parents who are heterozygous.

02:05 And if you do a little punnet square, you would see that these numbers are accurate, that there is a 25 % chance the offspring will be homozygous dominant.

02:16 And so we'll have two dominant alleles, 50 % chance that they will be heterozygous and a 25 % chance that they will be a homozygous recessive.

02:25 So the first two options are the dominant phenotype.

02:28 And so there's altogether a 75 % chance the offspring.

02:31 Will have the dominant phenotype.

02:33 And then the remaining 25 % chance that they will be homozygous recessive.

02:38 So knowing that now, we can go back and look at these other two crosses and make sure that it makes sense.

02:50 So we're going to do this green one over here real quick.

02:53 We see that there's two parents who are normal, and we know that being normal is the recessive phenotype, so both parents have to have recessive allele.

03:03 And we're told that 100 % of their offspring are also normal and have that recessive phenotype, which makes sense...

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