Mix Examples- Principles of Inheritance and Variation Questions in English

(A) $1$. Haemophilia is an $X$-linked recessive disorder. $A$ female carrier $(X^HX^h)$ has a $50\%$ chance of passing the defective $X^h$ chromosome to her sons,who will then express the disease.
$2$. Thalassemia is a quantitative problem because it involves the reduced synthesis of one of the globin chains of the haemoglobin molecule.
$3$. $A$ change in the whole set of chromosomes is called polyploidy,whereas aneuploidy refers to the gain or loss of one or more individual chromosomes.
$4$. Sickle cell anaemia is a qualitative problem because it results from a point mutation in the gene coding for the $\beta$-globin chain,leading to the substitution of glutamic acid with valine,which alters the structure and function of the haemoglobin molecule.

(C) The correct answer is $C$ and $D$ only.
$1$. In human $ABO$ blood grouping,the alleles $I^A$ and $I^B$ are co-dominant,meaning both are expressed equally in the $AB$ blood type,which is an example of Co-dominance.
$2$. The $ABO$ blood system is controlled by three alleles $(I^A, I^B, i)$,which is more than the two alleles typically found for a gene. This phenomenon is known as Multiple allelism.

(A) The wrong statement is: $A$. Alleles $b$ and $c$ also produce sugar.
Explanation:
$1$. The $ABO$ blood grouping in humans is controlled by the gene $I$,which has three alleles: $I^{A}$,$I^{B}$,and $i$.
$2$. The alleles $I^{A}$ and $I^{B}$ produce specific enzymes (glycosyltransferases) that add sugar polymers to the surface of red blood cells,forming antigens $A$ and $B$,respectively.
$3$. The allele $i$ does not produce any sugar or antigen.
$4$. When $I^{A}$ and $I^{B}$ are present together,both express themselves equally,a phenomenon known as co-dominance.
$5$. $I^{A}$ and $I^{B}$ are dominant over $i$,meaning if $I^{B}$ and $i$ are present,the phenotype will be blood group $B$ (due to $I^{B}$ expression).

(D) $Statement A$ is correct because according to the Law of Segregation,alleles of a gene pair segregate from each other during gamete formation,such that each gamete carries only one allele for a given trait.
$Statement B$ is correct because during the anaphase stage of mitosis,the centromere splits and the sister chromatids separate,moving towards opposite poles of the cell.
Since $Statement B$ describes a process of cell division (mitosis) and $Statement A$ describes the principle of inheritance (meiosis/gametogenesis),$Statement B$ is not the reason for $Statement A$.

(C) $1$. Incomplete Dominance in Antirrhinum sp. (snapdragon) results in an intermediate phenotype,matching $A-II$.
$2$. Co-dominance is exemplified by $ABO$ blood groups where both $A$ and $B$ alleles express themselves,matching $B-IV$.
$3$. Pleiotropy occurs where a single gene affects multiple traits,as seen in phenylketonuria,matching $C-III$.
$4$. Polygenic inheritance explains continuous traits like human skin colour,matching $D-I$.
Therefore,the correct matching is $A-II, B-IV, C-III, D-I$.