In a particular human family, John and his mother both have brachydactyly (a rare autosomal domi

step 1 In order to answer this question, let's talk about inheritance. In this case, it says a man with

In a particular human family, John and his mother both have...

Key Concepts

Genetic Linkage and Recombination

Genetic linkage occurs when genes are close together on the same chromosome and tend to be inherited together. The recombination frequency, often measured in centimorgans or map units, indicates the chance that a crossover event will separate two linked genes. This concept is key in determining how linked traits might be co-inherited and affects the probability calculations in genetic risk assessments.

Autosomal Dominant Inheritance

Autosomal dominant inheritance is a pattern where a single copy of a mutant allele on a non-sex chromosome is sufficient to cause the expression of the trait. This means that an affected individual has a 50% chance of passing the allele to each offspring, which is essential for predicting risk in familial genetic conditions.

Penetrance

Penetrance refers to the proportion of individuals with a disease-causing genotype who actually express the associated phenotype. Incomplete penetrance, where some individuals do not show symptoms despite carrying the mutation, significantly impacts risk assessments and genetic counseling.

Genotype versus Phenotype

The genotype is the genetic constitution at a particular locus, whereas the phenotype is the observable physical or biochemical characteristic resulting from the interaction of the genotype with the environment. Understanding this difference is fundamental to genetic analysis and predicting disease manifestation.

Independent Assortment and Unlinked Genes

Independent assortment describes how genes located on different chromosomes or far apart on the same chromosome are transmitted to offspring independently of one another. This principle allows for the multiplication of probabilities when calculating the likelihood of inheriting multiple traits simultaneously.

Transcript

00:02 In order to answer this question, let's talk about inheritance.

00:05 In this case, it says a man with hand in the seed, he is heterozygos.

00:08 In this case, let's use the age gene, okay? just for it not to be so confusing.

00:16 So, he is heterozygos, it says.

00:19 And a normal woman have two children.

00:21 So the woman is homo -sangoon excessive.

00:24 Let's make a pan in the square here, like this.

00:34 Okay? so it says, they have two children.

00:37 What is the probability that only, the second child has the disease.

00:43 So you want that the first child to be normal and the second child to be to have huntington disease in this order, okay, in this order.

00:53 So here you have two possibilities or four possibilities.

00:57 And out of those four possibilities, two are going to have handington disease.

01:02 It means two quarters, that is the same as one half, okay? four huntington disease and the remaining one half for normal.

01:10 So in this case, you have one half chances to be normal and one half chances to be handington disease in this order.

01:16 So in this order, you're going to have one quarter.

01:20 So there are one quarter chances for this couple to have their first child with a normal phenotype and a second child with huntington disease.

01:29 The next question says, what is the probability that only one of the children has a disease? so you want either this or this.

01:43 Okay? so you have one half and one half and this is equal to one quarter.

01:48 So you want either this or this because both are combinations or both a code for at least one, only one child who is affected.

01:58 Okay, here you have only one child who is affected and here you have only one child who is affected, but in this case, it is in the second child and this is in this case, it is in the first child, okay? so you want either this or this.

02:11 So when you have or you have to add.

02:14 So you have to add these two values and you're going to get to quarters that is the same as one half, and this is equal to 0 .5, which you want to build the answer in probabilities.

02:22 Okay? so this is the answer for the second question.

02:25 Question c says, what is the chance that none of the children has a disease? so you want normal and normal.

02:34 The chances to get normal is one half, and the chances to get normal is also one half.

02:38 So you have to multiply this and you'll get one quarter or 0 .25.

02:42 This is the answer for question c.

02:43 Question d says answer a through c assuming that the couple has had 10 children then it says okay, so now we have to answer the same questions but assuming that the child that this couple has 10 children okay, so let's go for option a it says what is the probability that only the second child has a disease? so if you have 10 and you want only the second to have a to be to have the disease you have this okay so you have one half chances to be normal for into this and all the remaining are going to be also this is going to be a he's going to have or this charlie is going to have handed on disease and all the game are going to be normal so you have one half here a one half one half one half one half because all the remaining children are going to have the same chance to be normal okay one half each pregnancy is independent from each other you remember okay it means each pregnancy is going to have one -half chances to be normal and one -half chances to be to have huntington disease.

03:54 So you have one -half to the power of 10, practically, because you have 10 times this value here.

04:05 So this is going to be equal to.

04:07 Let me use a calculator.

04:11 2 to the power of 10 is equal to 1 ,024.

04:17 So this is the answer for question d, okay? the first part of question d.

04:23 Then the next question or question b says what is the probability that only one of the children has a disease? so you have again, two, three, four, five, six, seven, eight, nine, ten.

04:35 You have ten children.

04:37 And you want that only one of the children has a disease.

04:41 So you want, for example, normal, handington, normal, normal, normal, normal, normal, normal, normal, normal, normal, normal, normal, normal, normal...

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