Q.Name a human genetic disorder due to the following :

Step 1 — Recall the defect in sickle cell anaemia

Sickle cell anaemia results from a point mutation that changes one amino acid (glutamic acid to valine) in the beta-globin chain — this alters the structure/quality of the globin molecule produced, not the amount made. This is a qualitative defect.

Step 2 — Recall the defect in Thalassemia

Thalassemia is caused by mutations (often deletions or defects in regulatory/synthesis machinery) that reduce or completely stop the synthesis rate of one of the globin chains (alpha or beta) — the globin chains produced are structurally normal, but fewer of them are made. This is a quantitative defect.

Step 3 — Evaluate the options …

Step 1 — Set the genotypes (X-linked recessive inheritance).

Colourblindness is carried on the X chromosome; $X^{C}$ = normal allele, $X^{c}$ = colourblind allele.

• Colourblind man: a male is hemizygous — one X only — so he is $X^{c}Y$.
• Carrier woman: phenotypically normal but heterozygous, $X^{C}X^{c}$.

Step 2 — Gametes.

• Father: $X^{c}$ and $Y$
• Mother: $X^{C}$ and $X^{c}$

Step 3 — Punnett square.

Step 1 — Read the pedigree.

• Generation I: an unaffected male × an unaffected female.
• Generation II: five children — an affected son, an affected daughter, and three unaffected children.
• Generation III: an unaffected Gen-II daughter married to an unaffected male produces an affected son plus two unaffected daughters.

Step 2 — Dominant or recessive?

The trait skips: both Gen-I parents are unaffected, yet affected children appear. A dominant allele must be expressed in at least one parent (an affected child of a dominant trait must have an affected parent). Since the phenotype disappears in a generation and reappears, it is carried silently by heterozygotes ⇒ the allele is recessive. Both parents are carriers ($Aa \times Aa \rightarrow \tfrac14\ aa$ affected).

This kills options (B) "Sex-linked dominant" and (D) "Autosomal dominant".

Step 3 — Autosomal or sex-linked (X-linked)?

Test the X-linked recessive hypothesis on the Gen-I family. An affected daughter would need genotype $X^a X^a$, i.e. one $X^a$ from her mother (a carrier, fine) and one $X^a$ from her father. But a father's only X carries the allele he expresses — so an $X^a$-bearing father would himself be affected. The Gen-I father is drawn unaffected. Contradiction. …

1. Define the two reproductive whorls

A complete flower has four whorls, of which two are reproductive:

• Androecium — made of stamens; this is the male whorl (anther + filament, producing pollen).
• Gynoecium (pistil) — made of carpels; this is the female whorl (stigma, style, ovary, producing ovules).

2. The classification of flowers by sex

The question's flower has both stamens and carpels ⇒ bisexual.

3. Why the other options are wrong

• (A) Asexual — asexual means reproduction without gametes/fusion at all (budding, fragmentation, vegetative propagation). A flower is by definition a sexual reproductive structure, so "asexual flower" is a contradiction. …

Step 1 — Understand the terminology

• Homogametic sex → produces only one type of gamete with respect to the sex chromosome.
• Heterogametic sex → produces two different types of gamete.

Step 2 — Apply it to male heterogamety

Male heterogamety covers two systems:

In both, the male is the one making dissimilar gametes; the female ($XX$) makes only $X$-bearing eggs and is homogametic. The sex of the offspring is therefore decided by the sperm.

Step 3 — Eliminate the other options …

1. Statement (A) — check the cross

Haemophilia is a sex-linked (X-linked) recessive disorder. Let $X^H$ = normal allele, $X^h$ = haemophilia allele.

A carrier mother is heterozygous $X^H X^h$ (she is normal, because the dominant $X^H$ masks $X^h$). Cross her with a normal father $X^H Y$:

A son receives his single X from his mother and a Y from his father. With no second X to carry a masking dominant allele, he is hemizygous and expresses whatever is on that X. Hence half the sons of a carrier mother are haemophilic — statement (A) is CORRECT. ✓

2. Why the other three are wrong

(B) "Thalassemia is a qualitative problem." ✗ — inverted. The standard contrast is:

So thalassemia is quantitative, not qualitative. …

The concept here is gamety — whether a sex produces identical or different gametes with respect to sex chromosomes. "Homo" means same, "hetero" means different. The system is named after the sex that is heterogametic, because that's the one that determines the offspring's sex.

In the XO system (found in grasshoppers, for example), females have two X chromosomes (XX) and produce only X-bearing eggs — they are homogametic. Males have only one X (XO) and produce two types of sperm: half with X, half with no sex chromosome (O). That makes males heterogametic.

In the XY system (humans, Drosophila), females are XX and produce only X eggs — again homogametic. Males are XY and produce X-bearing and Y-bearing sperm — heterogametic.

So in both systems, the female is homogametic and the male is heterogametic. The question asks for the example these systems represent — they are both cases of male heterogamety.

Let's walk through the options:

1. Male Homogamety — This would mean males produce only one type of gamete. That's false here; males in both systems produce two types.
2. Male Heterogamety — Correct. Males produce two different gamete types (X and O, or X and Y). …

Step 1 — The two vocabularies you need

Autosome vs allosome: autosomes are chromosome pairs 1–22; allosomes (sex chromosomes) are the X and Y.

Trisomy vs monosomy: these are aneuploidies, caused by the failure of chromatids to segregate during cell division (non-disjunction):

• Trisomy = one EXTRA chromosome ($2n+1$).
• Monosomy = one chromosome MISSING ($2n-1$).

Separately, a Mendelian disorder is one caused by an alteration/mutation in a SINGLE GENE (not a change in chromosome number).

Step 2 — Work through Column I

i. Autosomal trisomy → (s) Down's Syndrome.

An extra copy of chromosome 21 (trisomy 21) — chromosome 21 is an autosome. Karyotype $47$, i.e. $2n+1$. Features: short stature, small round head, furrowed tongue, partially open mouth, palm crease, retarded mental and physical development.

ii. Allosomal trisomy → (r) Klinefelter's Syndrome.

Karyotype 47, XXY — an extra X on the SEX chromosomes. The individual is masculine in development but has gynaecomastia (feminine development, e.g. breast development) and is sterile.

iii. Allosomal monosomy → (p) Turner's Syndrome.

Karyotype 45, XO — one of the X chromosomes is MISSING, again on the SEX chromosomes. Such females are sterile, have rudimentary ovaries and lack other secondary sexual characters.

iv. Cystic fibrosis → (q) Mendelian disorder. …

The key idea here is the sex determination system in organisms. In most mammals, including humans, males are heterogametic (XY) and females are homogametic (XX). But in some species — notably birds, some reptiles, and butterflies — the pattern is reversed: the female is the heterogametic sex. This system is denoted by the letters Z and W, where females are ZW and males are ZZ.

Let’s examine each option carefully.

1. Option (A): $XX - XY$

   This is the familiar mammalian system. Females are XX (homogametic — all eggs carry an X chromosome), and males are XY (heterogametic — sperm carry either X or Y). So here, male heterogamety is shown, not female.

2. Option (B): $ZZ - ZW$

   In this notation, males are ZZ (homogametic — all sperm carry Z), and females are ZW (heterogametic — eggs carry either Z or W). This is exactly female heterogamety. The female produces two types of gametes, determining the sex of the offspring.

3. Option (C): $XX - XO$

   This system is found in some insects like grasshoppers. Females are XX (homogametic), and males are XO (they have only one X chromosome, no second sex chromosome). Males produce sperm with either X or no sex chromosome — so again, male heterogamety.

4. Option (D): $XX - XXY$ …