Consider two blood polymorphisms that humans have in...

Consider two blood polymorphisms that humans have in addition to the ABO system. Two alleles $L^{\mathrm{M}}$ and $L^{\mathrm{N}}$ deter mine the $\mathrm{M}, \mathrm{N},$ and $\mathrm{MN}$ blood groups. The dominant allele $R$ of a different gene causes a person to have the $\mathrm{Rh}^{+}$ (rhesus positive) phenotype, whereas the homozygote for $r$ is $\mathrm{Rh}^{-}(\text {rhesus negative }) .$ Two men took a paternity dispute to court, each claiming three children to be his own. The blood groups of the men, the children, and their mother were as follows: $$\begin{array}{llll} \text { Person } & {3}{c} {\text { Blood group }} \\ \hline \text { husband } & \mathrm{O} & \mathrm{M} & \mathrm{Rh}^{+} \\ \text {wife's lover } & \mathrm{AB} & \mathrm{MN} & \mathrm{Rh}^{-} \\ \text {wife } & \mathrm{A} & \mathrm{N} & \mathrm{Rh}^{+} \\ \text {child 1 } & \mathrm{O} & \mathrm{MN} & \mathrm{Rh}^{+} \\ \text {child 2 } & \mathrm{A} & \mathrm{N} & \mathrm{Rh}^{+} \\ \text {child 3 } & \mathrm{A} & \mathrm{MN} & \mathrm{Rh}^{-} \\ \hline \end{array}$$ From this evidence, can the paternity of the children be established?

Consider two blood polymorphisms that humans have in addition to the ABO system. Two alleles $L^{\mathrm{M}}$ and $L^{\mathrm{N}}$ deter mine the $\mathrm{M}, \mathrm{N},$ and $\mathrm{MN}$ blood groups. The dominant allele $R$ of a different gene causes a person to have the $\mathrm{Rh}^{+}$ (rhesus positive) phenotype, whereas the homozygote for
$r$ is $\mathrm{Rh}^{-}(\text {rhesus negative }) .$ Two men took a paternity dispute to court, each claiming three children to be his own. The blood groups of the men, the children, and their mother were as follows:
$$\begin{array}{llll}
\text { Person } & {3}{c} {\text { Blood group }} \\
\hline \text { husband } & \mathrm{O} & \mathrm{M} & \mathrm{Rh}^{+} \\
\text {wife's lover } & \mathrm{AB} & \mathrm{MN} & \mathrm{Rh}^{-} \\
\text {wife } & \mathrm{A} & \mathrm{N} & \mathrm{Rh}^{+} \\
\text {child 1 } & \mathrm{O} & \mathrm{MN} & \mathrm{Rh}^{+} \\
\text {child 2 } & \mathrm{A} & \mathrm{N} & \mathrm{Rh}^{+} \\
\text {child 3 } & \mathrm{A} & \mathrm{MN} & \mathrm{Rh}^{-} \\
\hline
\end{array}$$
From this evidence, can the paternity of the children be established?

Key Concepts

Paternity Testing Using Blood Typing

This concept refers to the use of genetic markers, such as those found in the ABO, MNS, and Rh systems, to assess biological relationships. It involves comparing the possible genotypes and phenotypes of the child with those of the alleged parents to either support or exclude paternity based on known Mendelian inheritance rules.

Mendelian Inheritance

This concept involves understanding how alleles segregate and combine from parents to offspring according to Mendel's laws. It is crucial for determining the transmission of traits such as blood groups, as it explains patterns of dominant and recessive inheritance and codominance across various genetic systems.

ABO Blood Group System

This blood grouping system is determined by multiple alleles with codominant and recessive relationships. The system's inheritance pattern is used in paternity testing to see whether a child's blood type could be inherited from a potential parent, given the known phenotypes of the parents.

MNS Blood Group System

The MNS system is governed by a separate set of genes with alleles that are codominant, determining distinct M, N, and MN phenotypes. Understanding how these alleles are expressed helps in analyzing whether the blood group characteristics of a child are consistent with those of the alleged parents.

Rh Blood Group System

The Rh system involves a gene where the dominant allele (Rh+) masks the homozygous recessive state (Rh-). Knowing the inheritance pattern of Rh factor is essential when evaluating whether a child’s Rh status is biologically consistent with that of the parents.

Transcript

00:01 From the provided data, we cannot determine with 100 % accuracy the paternity of the children.

00:06 And so let's look at the evidence.

00:09 We know that m and n and a, b are codominant.

00:23 Rees, so the rh factor, so the recess factor, is easier to determine because you can either be plus plus, so you would have the plus, plus minus, you would have the plus on your, the rh factor on the blood cells, but you would be a carrier for negative.

00:43 And then no rh factor.

00:47 So that's classic like complete dominance inheritance pattern.

00:51 And so if we look at the husband, he's o -type blood, so he can only donate o -type alleles to the children.

01:01 He is m.

01:03 And so he can either be m -m or, oh, just m -m.

01:11 And then the rh factor, he could be plus plus or plus minus, which becomes important to identify the parents of child three.

01:26 Let's look at the wife.

01:29 She has a -type blood.

01:31 But if you look at child one in the table, that child has o -type blood.

01:36 And the wife's lover has a -b blood.

01:41 So that means that child is a product of the husband with the wife, and that the wife's a -type blood is a genotype i -a -little i to make child 1 -o -type blood.

01:55 So that would work.

01:57 And then the wife is in, so she must be in -in, and she's positive.

02:01 And again, we don't know if she's plus -plus or plus -minus, because both of these situations have a phenotype of r -h -plus.

02:10 And so for child three, the negative indicates we can't determine it because the husband and the wife could have had a child that's rh negative and so could the lover.

02:24 And so we can, let's put the lover up here above the husband.

02:28 He is a, b, blood.

02:32 So he couldn't have produced child one.

02:35 He is co -dominant in, and child one.

02:42 Is in, but there's no evidence that the husband and the wife couldn't have produced a child in that way.

02:48 So that is a poor indicator of paternity.

02:52 And the wife's lover is r .h.

02:55 Negative.

02:55 So he's negative for that.

02:58 Child one is positive, but we don't know if the child is plus plus or plus or plus minus...