hi everybody and welcome back to miss Angler's biology class I am Miss angler in today's video we are going to be doing a past exam question on genetics specifically this question is on blood groups and the level of difficulty is definitely hard or challenging because there are a lot of application questions and there are a lot of questions where you need to explain yourself as to why you have the outcome that you received now if you are new here don't forget to give this video a thumbs up and make sure you're subscribed with your notifications turned on because I post every Tuesday and Thursday now if you'd like to pause the video now and attempt the question please do so otherwise we're going to get into how you unpack these questions how you answer them for full marks and at the very end of the video I will also include a memo last but not least if you haven't got your hands on your cheat sheet just yet then you should head over to miss anger. co. so let's dive into this question so beginning here it says a woman is identified two possible men that could have been the father of her child below are the DNA results of a DNA profile paternity test and a blood paternity test now just a quick extra piece of information that's really really important is that you cannot confirm if a father is the father based off of his blood group you can just exclude fathers and the reason for that is there are plenty of men who have the same blood group so there are lots of men who are blood group a and blood group B that doesn't mean that that is their child however there are certain possible blood group outcomes that are not possible if you are not that blood group so hypothetically if we're talking about Dad let's say Dad is blood group ab and Mom is blood group O and they have a child who is O that cannot possibly be his child we don't even have to do any more than a a basic blood test because this child hasn't inherited any alals from this dad because he's only got an A blood group or a B blood group give and this child is O so where did the other O alal Come From do you see what I mean here so some combinations are possible um whereas others it's just not you're not able to actually confirm anything but other than that let's continue breaking down the question so I want to have a look at our table so our blood results here say the baby is is O our mother is blood group b um and then we've got two possible dads now without even looking at the DNA profile I'm not going to look there just yet I want to walk you through how I would be able to determine the dad just from the blood group potentially so remember blood group O is when we write it is two lowercase eyes for the alal so it' be something like that now then what is the mom's possible alals well the mother she would have been I with a capital B and because her baby has O blood group she would have also had a little I and she would have given that I to her child now out of the two other possible dads we can actually work out what their alals are so Dad one um he is blood group AB so the only possible alals he has is blood group AB like that whereas dad 2 is a a like this so he's got a blood group on both of his alals or he's a with a little I now that means that Dad one has nothing to offer to this child so already I can actually come to the conclusion that Dad one is not the father dad to on the other hand could be and he could be this option over here because he's going to give this lowercase ey now let's go over to the DNA profile and let's actually confirm this so remember when you do a profile file you want your alals to match up 50/50 between parents so let's say for example I want to match all the mother's alals to the baby so this one is matched to the mom let me see I'm going down here this one matches this one matches I'm just seeing if there is another one I think that's it I know that you might think oh this one but um no it's not because it's slightly offset and now let's do the dad so let's see who matches up with the baby so who matches with this Al this Dad this Al matches with this D this Leo matches with this Dad this one matches with this one this one matches with this one so I think it's uh it's pretty safe to say that Dad too is the father now we've confirmed it in both the blood test and the DNA profile let's go into our questions so first things first it says using the DNA profiling results explain why Dad 2 is the father now it is an explain question for three marks remember when you do an explain question you need to have a statement and then a reason in this instance you'll need to give two reasons to get your three marks so what is our statement well we're going to say something like all the black marks that don't match up with the mother they match with Dad number two so what you're doing is and I've short-handed this answer but your answer is all the black marks that the child has that do not match the mother match dad to which is true all the outstanding piece are coming from Dad too let's move on to our next question so it says explain why Dad one cannot be the father using the blood test results now that is where you are going to use these alals to help you support your answer and so how are you going to structure it well remember we're going to do an explain question for three marks so that means we need a statement and a reason and a reason so first things first let's start with the statement of the baby so our statement is going to be something like the child's alals is I I because they make blood group O now because of that Dad you're reasoning now dad one is blood group a b which means his alals are I a and I B now that reasoning leads you to your next reason because he is a b there is no way he could pass on the alal ey which is needed for blood group O and that's your reasoning for three marks now our final question says we need to use a genetic cross to show the percentage chance for the Mother and Dad to to have a baby with blood group O so remember a genetic cross is doing like a monohybrid cross and for Simplicity in this video I'm not going to redraw the entire cross for you I'm going to show you the memo and I'm going to point out the key things that you must include in order to calculate this now before we do that I want to remind you that the mother is blood group b and the uh father is as we've determined now a they want you to work with those but remember earlier on I did this little working out here at the beginning and I I showed you what the mom was remember that this is important to identify the mom's alals because you need to be able to use the correct alals for the mother and if you're thinking well how did I know for definite that that was the mom's alals remember the baby is O so we got to get one recessive ey from Mom and one recessive eye from Dad now here is the memo and you can have a look alongside here are for 231 and 232 you'll notice in question 232 there's another alternative answer our answer came from this particular one but this was also an alternative you could have given but I want to um zoom in on and focus our attention over here um on our genetic cross and I want to show you what we are getting our marks for so first things first whenever we are writing out a genetic cross we must include include the P1 and F1 in the margin that's what's going to get you one mark down here then at the beginning we need to write what mom is and dad is in their phenotype so blood type A times blood type B you write out their alals and those going to get you individual marks you then write out your gamuts as we see here you can do a punet square or a line diagram I prefer pun squares everybody they're much easier to use and you get a mark there as well and you end off your answer by showing your phenotype um in this instance they showed it as a ratio you could have also written it as a percentage the question didn't ask for a ratio and at the very end you get your final compulsory Mark over here for saying they have a 25% chance of having a blood group O child and we can confirm that by looking at the planet square and locating that child you will notice that this question says any5 + one compulsory Mark the compulsory Mark is over here so you must give this one to get six out of six the rest of the other five could be any of these five now if you're wondering I did not include any of the questions for 2.3.4 and 2.3.5 so you're not imagining things we didn't do those questions in this particular lesson I didn't think it was necessary for the focus now if you like this video don't forget to give it a thumbs up and make sure you're subscribed with your notifications turned on because I post every Tuesday and Thursday and I will see see you all again soon bye