CUET UG Biology Booster Test 2 Sex Determination and Mutation

Hermann Henking's 1891 study (iv-s) on insect spermatogenesis involved tracing a specific nuclear structure (i-p). He observed that 50% of the sperm cells received this structure (iii-r). Later scientific advancement revealed that this "X body" was, in fact, the X-chromosome (ii-q). Option A correctly aligns these historical and biological facts.

Henking observed the "X body" but explicitly stated he could not determine its exact nature or significance at the time, which is why he called it the "X" (unknown) body. Therefore, Statement I is incorrect. Later investigators, with better equipment and techniques, identified that this structure was indeed a chromosome. Thus, Statement II is correct.

Scientific progress proceeded by identifying the X body as a chromosome (1), followed by the observation of the XO mechanism in insects like grasshoppers (3). Once the sex-determining role was confirmed, the X was designated a sex chromosome (2). Subsequently, the remaining chromosomes were classified as autosomes (4).

In the XO mechanism, the female is XX and produces eggs that all contain one X chromosome. The male is XO, producing two types of sperm: 50% with an X and 50% without an X (O). When an O-sperm fertilizes an X-egg, the zygote is XO, which results in a male.

In humans, females produce only one type of gamete (X). Males produce two types (X and Y). Since the egg is always X, the sex is determined by the sperm that fertilizes the egg. Thus, stating the mother's egg determines the sex is incorrect. Options A, B, and C are all valid biological facts.

Drosophila follow the XY system, similar to humans. Males are XY and heterogametic, producing two types of gametes (X and Y). Females are XX and homogametic, producing only one type of gamete (X). Therefore, the statement that females produce two different types is false.

According to the given matching arrangement: XO Type (i) is matched with Grasshopper (p). XY Type (ii) is matched with Birds/Chicken (r). ZW Type (iii) is matched with Human (q). Haplodiploidy (iv) is matched with Honey Bee (s). Thus, the required matching is (i)-p, (ii)-r, (iii)-q, (iv)-s, which corresponds to Option D.

In the ZW-ZZ system, the female is the heterogametic sex (ZW). During meiosis, the female produces two types of eggs: 50% carrying the Z chromosome and 50% carrying the W chromosome. The sperm is always Z. Therefore, the sex of the offspring depends on which egg is fertilized, making the female the determinant of sex.

Autosomes are the chromosomes that are the same in both males and females (22 pairs). They carry genes for general bodily traits. Sex-specific physical traits (like those encoded by the Y chromosome) are on the sex chromosomes, not the autosomes. Therefore, Option C is false.

Statement I is correct because nondisjunction (failure of segregation) leads to gain or loss of chromosomes, known as aneuploidy (e.g., Down syndrome). Statement II is correct because a normal human diploid cell has 46 chromosomes, organized into 22 pairs of autosomes and 1 pair of sex chromosomes.

In the XY sex determination system, the ovum always carries an X chromosome. The sperm can carry either an X (resulting in a female) or a Y (resulting in a male). Therefore, the father is solely responsible for determining the sex of the child. Societies that blame women for having "only daughters" are operating on a fundamental misunderstanding of genetics.

Humans follow the XY system, where males produce X and Y sperm in a 1:1 ratio. Option D describes the ZW system (found in birds), which has no relevance to human biology. Therefore, it does not contribute to the 50% probability observed in human offspring.

Male honey bees (drones) develop from unfertilized eggs via parthenogenesis (1). Since they are haploid, they cannot produce gametes via meiosis, so they produce sperm by mitosis (2). They have no father because they come from an unfertilized egg (3) and have no sons (if they mate, they produce daughters), so they have grandsons rather than sons (4).

In honey bees, the female (queen/worker) is diploid (2n = 32). The male (drone) is haploid (n = 16). Because the drone is already haploid, he produces sperm via mitosis, meaning the sperm will have the same number of chromosomes as the drone, which is 16.

Biological diversity and genetic variation are primarily driven by two phenomena: mutation (spontaneous changes in DNA) and recombination (shuffling of genes during meiosis). Fertilization adds variation by combining different parental genomes, but recombination is the key internal genetic variation mechanism mentioned alongside mutation in NCERT.

• According to the revised matching: Point Mutation (i) is paired with deletions and insertions of base pairs (q). Frame-shift Mutation (ii) is paired with change in a single base pair (p). Deletion (iii) is paired with gain of a DNA segment (s). Insertion (iv) is paired with loss of a DNA segment (r). These pairings produce the combination (i)-q, (ii)-p, (iii)-s, (iv)-r, which corresponds to Option B.

Since genes are physical segments of DNA located on chromosomes, any structural change to the chromosome (aberration) inevitably affects the genes located within or near the site of the change. Option B correctly identifies this structural dependency.

Cancer is a disease of genomic instability. In cancer cells, the regulatory systems that maintain chromosomal integrity are compromised, leading to frequent deletions, duplications, and translocations. Therefore, cancer cells are a primary site for observing chromosomal aberrations.

The passage explicitly states: "The sex determination in honey bee is based on the number of sets of chromosomes an individual receives." An offspring with two sets (diploid) develops as a female, while one set (haploid) develops as a male.

The passage states: "the males have half the number of chromosomes than that of a female." If a female has 32 chromosomes, then the male will have 32 / 2 = 16 chromosomes.