Tim and Jan both have freckles (see Module 9.9 ), but their son Mike does not. Show with a Punne

Tim and Jan both have freckles (see Module 9.9 ), but their...

Key Concepts

Mendelian Inheritance

Mendelian inheritance refers to the principles, discovered by Gregor Mendel, that describe how traits are passed from parents to offspring through discrete units of inheritance called alleles. These principles include the laws of segregation and independent assortment, which help predict phenotypic outcomes in progeny.

Punnett Square

A Punnett square is a visual tool used in genetics to map out and predict the possible genotypes and phenotypes of offspring from a genetic cross. It systematically shows the combinations of parental alleles, allowing for the calculation of probabilities for the traits of interest.

Dominant and Recessive Alleles

Dominant and recessive alleles are fundamental to understanding genetic traits. A dominant allele expresses its trait even when present in only one copy, while a recessive allele only manifests its trait when two copies are present. This relationship explains why individuals carrying one dominant allele can still produce offspring with a recessive phenotype.

Probability in Genetic Inheritance

Probability in genetic inheritance involves calculating the likelihood of various genetic outcomes based on parental genotypes. By applying principles such as the multiplication rule for independent events, one can determine the chances of specific traits appearing in offspring over multiple generations.

Transcript

00:01 This question is asking, tim and jan both have freckles, but their son mike does not.

00:05 Show with the punnet square how this is possible.

00:08 If tim and jan have two more children, what is the probability that both will have freckles? so here we've included the image from module 9 .9 from the textbook, and it shows that freckles are a dominant trait, and no freckles is a recessive trait.

00:22 And that actually highlights the point that what is considered normal, quote unquote, is not necessarily what is dominant.

00:30 Right so the majority of people don't have freckles and that is a recessive trait so that is also a good thing to note now for the first part of the question show with the pundit square how this is possible we are going to look at the parents first so tim and jan both have freckles but the son does not so if it's a dominant treat we said freckles are a dominant trait right so we're going to note freckles as capital f no freckles as lowercase f okay so if dominant trait for freckles is what the parents have, but mike does not have the dominant trait, that only means that he must be homozygous recessive.

01:14 So he is going to be lowercase ff.

01:19 Okay.

01:20 How did he get that trait? well, this is when we do a punnet square and we kind of have to reverse engineer it.

01:29 So we're going to say that, well, mike was the offspring from his parents, and so he is recessive.

01:41 And that means that one of these lowercase fs came from one of his parents.

01:48 Then the other one also came from one of his parents.

01:51 So that means that his parents must have the alleles for lowercase f.

01:57 Now, tim and jan both have freckles, meaning that they have the dominant trait.

02:04 That means they both exhibit this capital f right here.

02:08 But we also said that they also have this lowercase f, right? so both tim and jan will have that lowercase f there.

02:21 Okay.

02:23 So what does that mean? that means this is the genetic breakdown for both his parents so both his parents must have had that the capital f allele okay so how do we denote that on a punta square we would take this capital f move it right over here right and same thing for this this capital f right here and move it down so now we have a punta square that we can fill out so we need know that his parents are heterozygous dominant for freckles.

03:04 Mike has no freckles, so he is homozygous recessive.

03:08 So now let's figure out the second part of the question, if tim and jan have two more children, what is the probability that both will have freckles? so we just have to fill out the rest of the pundit square.

03:21 Okay, so we are going to do the normal procedure.

03:24 We take our parent from up top, bring down the lowercase f, and from the side, bring across uppercase f now same thing capital f lowercase f and capital f capital f okay so what do we have here once again looking at our two symbols that we started off with we are going to see that so obviously right here make it blue this would have been mike right mike has no freckles because he is homozygous recessive...

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