Individuals affected by a condition known as polydactyly have extra fingers or toes. The followi

Individuals affected by a condition known as polydactyly...

Key Concepts

Dominant vs Recessive Alleles

Dominant alleles are those that express their phenotype even when only one copy is present, whereas recessive alleles require two copies to be expressed. This distinction is crucial for understanding the phenotype observed in individuals and for predicting the probability of occurrence of a trait in offspring, which is especially relevant when deducing the inheritance pattern from a pedigree.

Genotype Deduction

Genotype deduction involves inferring the genetic makeup of individuals from their observable characteristics (phenotype) and the inheritance pattern shown in a pedigree. By applying the principles of Mendelian inheritance, one can determine whether individuals are homozygous or heterozygous for a given trait, which is essential for predicting trait inheritance in future generations.

Pedigree Analysis

Pedigree analysis is a graphical representation of family relationships and observed phenotypes across generations. It is a key technique used to deduce the mode of inheritance (e.g., dominant, recessive, sex-linked) of a particular trait by tracking which individuals are affected and how the trait is passed from one generation to the next.

Mendelian Inheritance

Mendelian inheritance refers to the patterns by which traits are transmitted from parents to offspring according to laws first described by Gregor Mendel. This concept includes the understanding of how alleles come in pairs, segregate during the formation of gametes, and recombine at fertilization. It provides a foundation for analyzing how traits, whether dominant or recessive, are expressed in a family pedigree.

Sex-linked Inheritance

Sex-linked inheritance involves genes that are located on the sex chromosomes, leading to different patterns of transmission between males and females. This concept helps in determining whether a trait, based on its distribution among genders in a pedigree, is associated with either the X or Y chromosome, or if it is autosomal.

Transcript

00:01 Okay, in order to answer this question, we have to talk about pedigris.

00:03 Okay? remember, first, you have to make yourself a question.

00:07 And this in it is, is there father son transmission? if the answer is no, then it is an x -linked disorder.

00:19 Okay? and also, if males are more affected than females, then it is an x -linked recessive.

00:27 Okay? and if females are more affected than males, then it is an ex -linked dominant disease.

00:35 And what if your answer is yes? and also, if there is modern transmission, then it is an autosomal disorder.

00:51 Okay.

00:51 And also, if there is horizontal transmission, then it is autosomal excessive disease.

01:02 It means a horizontal transmission is that, for example, you have a guy that is with a disease here.

01:10 And he marries a woman and they have family, they have family, but none of them has a disease again.

01:18 And like around here, for example, they marry again.

01:25 And, okay, something like this.

01:34 And like around here, they have another song with a disease.

01:39 So this is not happening in a horizontal way.

01:42 An horizontal, i'm sorry, in a vertical way.

01:44 A vertical way would be like if this guy is affected too, affected, affected, affected if this is an horizontal transmission.

01:51 A vertical transmission, i'm sorry.

01:53 But an horizontal transmission would be if here you have a person with a disease and another person with a disease would appear like around here.

02:01 So it is kind of a horizontal.

02:04 Okay.

02:05 So when there is an horizontal transmission, it is autosomal recessive.

02:08 And when there is a vertical transmission, it's going to be an autosomal dominant disease.

02:19 Okay, with this knowledge, we can answer the question looking at the pedigree.

02:24 As you can see in this pedigree, there is a lot of vertical transmission, okay? because here you have a woman with a disease, and she has a daughter with a disease, a son with a disease, and this son with a disease has more sons with a disease, and the same with a disease.

02:40 Same here so it is likely to be a dominant disease okay well practically it is a dominant disease okay it is a dominant disease but we don't know yet if it is an ex -linked disease or an autosomal disease okay and we have to look at this there is father son transmission there you have father son transmission and also father son transmission so yes the answer is yes so it is an auto -send transmission abdominal disease, autosomal dominant disease, okay? and why? well, because, for example, in this case here, if it was an x -link dominant disease, then you would have this, that this guy, genotype would be this, when x -prime is a mutant allele, okay? and here you would have a normal woman, because she can't have the mutant allele because she would have a disease.

03:47 So you would have this cross, the father with a disease and the mother without a disease.

03:54 You solve this part of the square and you would have this.

04:03 You would have that all your daughters would have the disease.

04:08 But this is not true because this daughter does not have the disease.

04:12 So because of this, you can see that that's the same.

04:16 That an ex -linked dominant inheritance pattern does not fit in this pedigree.

04:21 Okay? so, practically, this is not ex -linked dominant and it is autosomal dominant.

04:29 Now, now that we know what type of inheritance pattern this pedigree is, then they ask us, well, the question says, from the pedigree, can you tell if podidactility comes from a dominant or it says it is a little? yes, and it is from a dominant allele, okay? from a dominant allele.

04:52 This is question number one.

04:54 Then it says, is the trait sex linket? no, it is not sex linket.

05:00 No.

05:01 It is autosomal.

05:05 Okay? then it says, as far as you can determine, what is the genotype of each person in this pedigree.

05:12 Okay, so as we know that it is autosomal dominant, let's state the alias.

05:16 This is the dominant, or practically, the allele for polydactyl...

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