Q.ZZ / ZW type of sex determination is seen in:

Showing the 12 most recent of 15 on this concept.

1. TG EAPCET 2026Set ap-2026-05-05-FN1 markMCQ
   Q.Trisomy of $23^{\text{rd}}$ chromosome in male results in (A) Turner syndrome (B) Down syndrome (C) Edward syndrome (D) Klinefelter syndrome

   ›Reveal solutionSolution

   Trisomy of the 23rd chromosome in a male means an extra sex chromosome (XXY), which causes Klinefelter syndrome. The correct option is (D).

   The key here is understanding what "trisomy of the 23rd chromosome" means. Humans have 23 pairs of chromosomes — 22 pairs of autosomes and 1 pair of sex chromosomes (the 23rd pair). In a normal male, the sex chromosome pair is XY. Trisomy means having three copies of a particular chromosome instead of the usual two. So trisomy of the 23rd chromosome in a male means the sex chromosome constitution is XXY — two X chromosomes and one Y.

   Now, which syndrome does XXY produce? That is Klinefelter syndrome. Let’s walk through the options to see why the others are wrong.

   1. Turner syndrome results from monosomy of the X chromosome in females — a single X (45,X). That is a missing sex chromosome, not an extra one. So it cannot be trisomy of the 23rd.

   2. Down syndrome is trisomy of chromosome 21, not the 23rd. It is an autosomal trisomy, not a sex chromosome trisomy. So this is a common confusion — students sometimes mix up the chromosome numbers.

   3. Edward syndrome is trisomy of chromosome 18, another autosomal trisomy. Again, not the 23rd. …

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2. TG EAPCET 2026Set ap-2026-05-05-FN1 markMCQ
   Q.If the blood groups of parents are homozygous for A and homozygous for B blood groups, these blood groups are not expected in their children (A) A, AB, O (B) A, B, O (C) B, AB, O (D) A, B, AB

   ›Reveal solutionSolution

   When one parent is homozygous A (genotype $I^A I^A$) and the other is homozygous B ($I^B I^B$), all children inherit one $I^A$ and one $I^B$ allele, giving only blood group AB. So groups A, B, and O are not expected.

   The key here is understanding how blood groups are inherited. The ABO system is controlled by a single gene with three alleles: $I^A$, $I^B$, and $i$. Both $I^A$ and $I^B$ are dominant over $i$, but they are codominant with each other — meaning if both are present, both are expressed, giving the AB blood group.

   When a parent is homozygous for a blood group, it means they carry two copies of the same allele. So a homozygous A parent has genotype $I^A I^A$, and a homozygous B parent has genotype $I^B I^B$.

   Now let’s work through what happens in their children.

   1. Gamete formation

      The $I^A I^A$ parent can only produce gametes carrying the $I^A$ allele.

      The $I^B I^B$ parent can only produce gametes carrying the $I^B$ allele.

   2. Fertilization

      Every child receives one allele from each parent. So every child gets exactly one $I^A$ and one $I^B$ — the only possible genotype is $I^A I^B$.

   3. Resulting blood group

      Since $I^A$ and $I^B$ are codominant, the $I^A I^B$ genotype expresses as blood group AB.

      No other combination is possible.

   4. Which groups are not expected?

      The children cannot have: …

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3. TG EAPCET 2025Set ap-2025-04-29-AN1 markMCQ
   Q.In several fungi and plants, the bisexual condition is denoted by (A) Homothallic and monoecious (B) Heterothallic and monoecious (C) Homothallic and dioecious (D) Heterothallic and dioecious

   ›Reveal solutionSolution

   The question asks for the terms that describe the bisexual condition in fungi and plants. In fungi, “homothallic” means both sexes on the same thallus (bisexual); in plants, “monoecious” means male and female flowers on the same plant (bisexual). So the correct pairing is homothallic and monoecious.

   The key here is to match the biological terminology to the concept of bisexuality — having both male and female reproductive structures in the same organism. Different kingdoms use different words for the same idea, and this question tests your ability to translate across them.

   1. In fungi, the term “thallus” refers to the body of the fungus. If a single thallus produces both male and female gametes (or gametangia), it is called homothallic (“same thallus”). If two different thalli are needed — one male, one female — it is heterothallic. So the bisexual condition in fungi is homothallic.

   2. In plants, the term “monoecious” comes from Greek monos (single) and oikos (house) — meaning “one house.” A monoecious plant has separate male and female flowers on the same individual (e.g., maize, cucumber). That is the bisexual condition at the organism level. “Dioecious” (“two houses”) means male and female flowers are on separate plants (e.g., papaya, date palm), which is unisexual at the organism level. …

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4. TG EAPCET 2025Set ap-2025-04-29-AN1 markMCQ
   Q.Consider the following statements Assertion (A): In human beings, Y-linked genes of non homologous part are called holandric genes. Reason (R): Y-chromosome is present in males only The correct answer is (A) Both (A) and (R) are true, (R) is the correct explanation of (A) (B) Both (A) and (R) are true, (R) is not the correct explanation of (A) (C) (A) is true, but (R) is false (D) (A) is false, but (R) is true

   ›Reveal solutionSolution

   Holandric genes are Y-linked genes found only in males since the Y chromosome is male-specific; the reason correctly explains why these genes show this pattern of inheritance. The correct option is (A).

   Understanding Sex Chromosomes and Gene Inheritance

   In human genetics, sex chromosomes (X and Y) determine biological sex and carry genes beyond just sex determination. The X and Y chromosomes have both homologous regions (where they can pair during meiosis) and non-homologous regions (unique to each chromosome).

   The key concept here involves understanding what happens with genes located in the non-homologous portion of the Y chromosome—the part that has no corresponding region on the X chromosome.

   Evaluating the Assertion

   Assertion (A): "In human beings, Y-linked genes of non homologous part are called holandric genes."

   Let's break this down:

   1. Holandric genes are indeed genes located on the Y chromosome, specifically in the non-homologous region (the region unique to Y that doesn't pair with X).

   2. These genes are passed exclusively from father to son, creating a strict patrilineal inheritance pattern.

   3. Examples include genes for testis development (SRY gene), some spermatogenesis factors, and certain genes controlling male-specific traits.

   This assertion is TRUE.

   Evaluating the Reason

   Reason (R): "Y-chromosome is present in males only"

   1. In humans, the typical sex chromosome composition is:

      • Males: XY (one X, one Y)
      • Females: XX (two X chromosomes, no Y)

   2. Therefore, the Y chromosome is indeed present only in males (barring rare chromosomal abnormalities).

   This reason is TRUE.

   Determining the Relationship

   Now the critical question: Does (R) correctly explain (A)? …

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5. TG EAPCET 2025Set ap-2025-04-29-FN1 markMCQ
   Q.Consider the following statements Assertion (A): In hymenopteran insects, sperms are produced by mitosis Reason (R): Male hymenopteran insects are haploid The correct answer is (A) Both (A) and (R) are true, (R) is the correct explanation of (A) (B) Both (A) and (R) are true, (R) is not the correct explanation of (A) (C) (A) is true, but (R) is false (D) (A) is false, but (R) is true

   ›Reveal solutionSolution

   In hymenopteran insects (ants, bees, wasps), males are haploid and produce sperm by mitosis, not meiosis. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

   The key here is understanding haploidy and sex determination in hymenopterans. In these insects, females develop from fertilized (diploid) eggs, while males develop from unfertilized (haploid) eggs through a process called arrhenotokous parthenogenesis. This means males have only one set of chromosomes — they are haploid.

   Now, think about what happens when a haploid organism needs to produce gametes. Normal meiosis would halve the chromosome number, but a haploid cell cannot undergo reduction division — it would produce inviable gametes with zero chromosomes. So nature has a clever workaround: male hymenopterans produce sperm by mitosis instead. Each sperm is an exact copy of the male's haploid genome, which is exactly what's needed to fertilize an egg and restore diploidy in the female offspring.

   Let's break it down step by step.

   1. Why the Reason (R) is true

      Male hymenopterans (drones in honeybees, for example) develop from unfertilized eggs. Since no sperm contributed genetic material, the egg's nucleus alone forms the embryo — it is haploid ($n$). This is a well-established biological fact.

   2. Why the Assertion (A) is true

      Because the male is haploid, it cannot undergo meiosis to produce sperm — meiosis would reduce the chromosome number to $n/2$, which is not viable. Instead, the cells in the testes divide by mitosis, producing haploid sperm that are genetically identical to the male parent. This is a direct adaptation to haploidy.

   3. How (R) explains (A) …

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6. TG EAPCET 2023Set ap-2023-05-10-FN1 markMCQ
   Q.Assertion (A): In honey bees drone has no father but has grand father Reason (R): Drones develop by parthenogenesis from ova. The correct option among the following is (A) (A) and (R) are true, (R) is the correct explanation of (A) (B) (A) and (R) are true, but (R) is not the correct explanation of (A) (C) (A) is true but (R) is false (D) (A) is false but (R) is true

   ›Reveal solutionSolution

   In honey bees, drones are haploid males produced by parthenogenesis from unfertilized eggs, so they have no father (since they come from the queen’s unfertilized ova) but do have a grandfather (the queen’s father). Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

   The key concept here is haplodiploid sex determination in honey bees. In this system, females (queens and workers) develop from fertilized eggs and are diploid, while males (drones) develop from unfertilized eggs and are haploid. This unusual reproductive biology leads to the peculiar family relationships described in the question.

   Let’s break it down step by step.

   1. How drones are produced

      A queen honey bee stores sperm from mating flights but can control whether an egg gets fertilized as it passes through her reproductive tract. If she lays an unfertilized egg, it develops into a drone — a male. This process is called parthenogenesis (development from an unfertilized egg). So the drone’s only genetic contribution comes from the queen’s egg; there is no sperm involved.

      Drone: $n$ (haploid) from unfertilized egg → no father.

   2. Why the drone has no father

      Since the drone develops from an unfertilized egg, there is no male parent. The queen is the drone’s mother, but there is no father. This is a direct consequence of parthenogenesis. So Assertion (A) — “drone has no father” — is true.

   3. Why the drone has a grandfather

      The drone’s mother (the queen) is diploid and has both a mother and a father. The queen’s father is a drone (since only drones are male). That drone is the grandfather of the original drone. So the original drone does have a grandfather — the father of the queen.

      Tip

      Think of it this way: the drone’s mother (queen) has a father (a drone), so that makes him the drone’s maternal grandfather. The drone inherits no genes from a father, but the family relationship still exists through the mother.

   4. Evaluating Reason (R) …

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7. TG EAPCET 2023Set ap-2023-05-10-AN1 markMCQ
   Q.The following are the components of male reproductive system of man in the order I. Retetestis  II. Ejaculatory duct III. Vasa efferentia  IV. Seminiferous tubules V. Vas deferens  VI. Urethra  VII. Epididymis (A) IV $\rightarrow$ I $\rightarrow$ III $\rightarrow$ VII $\rightarrow$ V $\rightarrow$ II $\rightarrow$ VI (B) I $\rightarrow$ IV $\rightarrow$ V $\rightarrow$ III $\rightarrow$ II $\rightarrow$ VI $\rightarrow$ VII (C) VII $\rightarrow$ II $\rightarrow$ V $\rightarrow$ III $\rightarrow$ I $\rightarrow$ IV (D) IV $\rightarrow$ I $\rightarrow$ V $\rightarrow$ VII $\rightarrow$ III $\rightarrow$ II $\rightarrow$ VI

   ›Reveal solutionSolution

   The path of sperm from production to exit follows a fixed anatomical sequence: seminiferous tubules → rete testis → vasa efferentia → epididymis → vas deferens → ejaculatory duct → urethra. The correct order is option (A).

   The question asks for the correct sequence of structures through which sperm travel from their site of production to the outside. This is a pure anatomy question — no tricks, just a clear mental map of the male reproductive tract. The key is to start where sperm are made and then follow the duct system step by step.

   Sperm are produced in the seminiferous tubules inside each testis. From there, they move into a network of channels called the rete testis. Next, they pass through several small ducts called the vasa efferentia (singular: vas efferens), which carry them out of the testis and into the epididymis — a long coiled tube where sperm mature and are stored. When ejaculation occurs, sperm travel from the epididymis into the vas deferens (a thick muscular tube), then into the ejaculatory duct (formed by the union of the vas deferens and the seminal vesicle duct), and finally through the urethra to exit the body.

   Let’s lay this out step by step.

   1. Seminiferous tubules (IV) — This is where spermatogenesis occurs. Sperm are released into the lumen of these tubules.
   2. Rete testis (I) — The seminiferous tubules converge into a network of channels within the testis. Sperm flow into this network.
   3. Vasa efferentia (III) — From the rete testis, 15–20 small ducts (vasa efferentia) pierce the tunica albuginea and carry sperm into the head of the epididymis.
   4. Epididymis (VII) — Sperm enter the epididymis (head → body → tail) for maturation and storage. This is the only place where sperm become motile and capable of fertilisation.
   5. Vas deferens (V) — During ejaculation, sperm are propelled from the tail of the epididymis into the vas deferens, a long muscular duct that runs from the scrotum into the pelvic cavity. …

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8. TG EAPCET 2023Set ap-2023-05-11-AN1 markMCQ
   Q.Pore in the foetal heart of human beings is (A) Foramen Manro (B) Foramen Ovale (C) Foramen Magnum (D) Fossa Ovalis

   ›Reveal solutionSolution

   The pore in the fetal heart that allows blood to bypass the non-functional lungs is the Foramen Ovale, which is option (B).

   Concept and Intuition

   In human beings, before birth, a fetus develops inside the mother's womb. During this period, the fetal lungs are not yet functional for gas exchange; the fetus receives oxygen and nutrients, and eliminates waste, through the placenta from the mother's blood. This unique situation requires a special circulatory system that allows blood to bypass the lungs.

   The fetal heart has several adaptations, known as shunts, to redirect blood away from the pulmonary circulation (lungs) and towards the systemic circulation (body). One of the most important of these shunts is an opening directly between the two upper chambers (atria) of the heart. This opening ensures that oxygenated blood returning from the placenta can quickly reach the systemic circulation without first passing through the non-functional fetal lungs.

   Step-by-step Explanation

   1. Understanding Fetal Circulation: In a fetus, oxygenated blood from the placenta enters the right side of the heart. Since the lungs are not yet used for breathing, there's no need for all this blood to go to the pulmonary arteries and then to the lungs. Instead, the blood needs to be shunted to the left side of the heart to be pumped to the rest of the body.

   2. Identifying the Interatrial Opening: The specific "pore" or opening in the wall between the right atrium and the left atrium of the fetal heart serves this exact purpose. It allows blood to flow directly from the right atrium to the left atrium, bypassing the pulmonary circulation.

   3. Naming the Structure: This crucial opening in the fetal heart is called the Foramen Ovale. The term "foramen" means an opening or hole, and "ovale" refers to its oval shape.

      Important

      The Foramen Ovale is a vital shunt in fetal circulation, allowing oxygenated blood to bypass the non-functional lungs by flowing directly from the right atrium to the left atrium.

   4. Function of the Foramen Ovale:

      • Blood from the placenta (oxygen-rich) enters the right atrium.
      • A significant portion of this blood passes through the Foramen Ovale into the left atrium.
      • From the left atrium, it goes to the left ventricle and then is pumped into the aorta to supply the head, upper limbs, and the rest of the body.
      • This mechanism ensures that the most oxygenated blood reaches the developing brain and other vital organs. …

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9. TG EAPCET 2023Set ap-2023-05-11-AN1 markMCQ
   Q.If the blood group of father is A (homozygous) and that of mother is AB, these blood groups are not expected in their children (A) A, AB (B) B, AB (C) O, AB (D) B, O

   ›Reveal solutionSolution

   The inheritance of ABO blood groups follows Mendelian principles, with $I^A$ and $I^B$ being codominant and dominant over $i$. A homozygous A father ($I^A I^A$) and an AB mother ($I^A I^B$) can only produce children with blood groups A or AB. Therefore, blood groups B and O are not expected in their children.

   The ABO blood group system in humans is a classic example of multiple alleles and codominance. Understanding how these alleles combine is key to predicting the blood groups of offspring.

   The gene controlling ABO blood groups has three alleles: $I^A$, $I^B$, and $i$.

   • The alleles $I^A$ and $I^B$ are codominant to each other, meaning that if both are present, both traits are expressed (resulting in blood group AB).
   • Both $I^A$ and $I^B$ are dominant over the allele $i$. This means that if $I^A$ is present with $i$, the blood group is A; if $I^B$ is present with $i$, the blood group is B.
   • The allele $i$ is recessive, so it only expresses itself when two copies are present ($ii$), resulting in blood group O.

   Here's a summary of genotypes and their corresponding phenotypes:

   Genotype	Phenotype (Blood Group)
   $I^A I^A$	A
   $I^A i$	A
   $I^B I^B$	B
   $I^B i$	B
   $I^A I^B$	AB
   $i i$	O

   To determine the expected blood groups of the children, we first need to establish the genotypes of the parents and then use a Punnett square to see the possible combinations of alleles in their offspring.

   1. Determine the genotypes of the parents.

      • The father has blood group A and is homozygous. Since blood group A can be $I^A I^A$ or $I^A i$, a homozygous A father must have the genotype $I^A I^A$.
      • The mother has blood group AB. The only genotype for blood group AB is $I^A I^B$.

   2. Determine the possible gametes from each parent.

      • The father, with genotype $I^A I^A$, can only produce gametes carrying the $I^A$ allele.
      • The mother, with genotype $I^A I^B$, can produce two types of gametes: those carrying the $I^A$ allele and those carrying the $I^B$ allele.

   3. Use a Punnett square to predict the genotypes and phenotypes of the offspring. …

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10. TG EAPCET 2023Set ap-2023-05-11-FN1 markMCQ
    Q.Assertion (A): In cockroaches the sex of offspring depends on the fertilizing sperm. Reason (R): Cockroach males are heterogametic with XO chromosomes The correct option among the following is (A) A and R are true. R is the correct explanation of A (B) A and R are true, but R is not the correct explanation of A (C) A is true but R is false (D) Both A and R are false.

    ›Reveal solutionSolution

    Cockroach males are XX/XO heterogametic, so the sperm determines offspring sex; both statements are true and R correctly explains A. The answer is (A).

    Sex determination in cockroaches follows the XX/XO system, a chromosomal mechanism where males produce two types of gametes. Understanding this system reveals why the fertilizing sperm dictates the sex of the offspring.

    In the XX/XO system, females carry two X chromosomes (XX) and are homogametic—they produce only one type of egg, each carrying a single X. Males, by contrast, carry only one X chromosome with no corresponding partner (XO, where O denotes absence), making them heterogametic. During meiosis, a male produces two kinds of sperm: half carry an X chromosome, and half carry no sex chromosome at all.

    When fertilization occurs, the outcome depends entirely on which sperm type fuses with the egg:

    1. If an X-bearing sperm fertilizes the egg (X): The zygote receives XX and develops into a female.

    2. If an O-bearing sperm (no sex chromosome) fertilizes the egg (X): The zygote receives XO and develops into a male.

    Because the egg always contributes an X, while the sperm may contribute either X or nothing, the sperm determines the sex. This makes Assertion (A) true.

    Now examine Reason (R): it states that cockroach males are heterogametic with XO chromosomes. This is factually accurate—males do have the XO constitution and produce two types of gametes, which is precisely what "heterogametic" means. …

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11. TG EAPCET 2023Set ap-2023-05-11-FN1 markMCQ
    Q.Arrhenotoky means (A) Female parthenogenesis (B) Male parthenogenesis (C) Homozygosity (D) Heterozygosity

    ›Reveal solutionSolution

    Arrhenotoky is a form of parthenogenesis in which unfertilized eggs develop into males while fertilized eggs produce females. The answer is (B) Male parthenogenesis.

    Parthenogenesis is reproduction from an unfertilized egg, without the genetic contribution of a male gamete. In most organisms this would seem to lead only to females, but nature has evolved several variations. Arrhenotoky is one such specialized form.

    The term breaks down from Greek roots: arrhen (male) + tokos (birth). This etymology directly tells us what happens—males are born from unfertilized eggs.

    How arrhenotoky works

    In arrhenotokous species, the sex-determination system is typically haplodiploid:

    • Unfertilized eggs → remain haploid (n) → develop into males
    • Fertilized eggs → become diploid (2n) → develop into females

    This creates an unusual genetic situation where males have no father and cannot pass on genes from a paternal grandfather, yet they have grandfathers on their mother's side.

    Classic examples

    Arrhenotoky is widespread in Hymenoptera (bees, wasps, ants). A queen bee stores sperm and controls fertilization:

    • When she releases sperm to fertilize an egg: a diploid female (worker or future queen) develops
    • When she lays an unfertilized egg: a haploid male (drone) develops

    The same mechanism occurs in many mites, thrips, and some beetles. …

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12. TG EAPCET 2022Set ap-2022-07-30-FN1 markMCQ
    Q.Assertion (A): In honey bees, males have no father and they cannot have sons, but they do have grand fathers and grand sons. Reason (R): They develop directly by parthenogenesis from unfertilised ova. The correct option among the following is (A) (A) is true, (R) is true and (R) is the correct explanation for (A) (B) (A) is true, (R) is true but (R) is not the correct explanation for (A) (C) (A) is true but (R) is false (D) (A) is false but (R) is true

    ›Reveal solutionSolution

    In honey bees, males (drones) are haploid and develop from unfertilised eggs via parthenogenesis, which explains why they have no father, cannot have sons, but can have grandfathers and grandsons — both Assertion and Reason are true, and the Reason correctly explains the Assertion.

    The key here is understanding the haplodiploid sex-determination system in honey bees. Females (queens and workers) are diploid, developing from fertilised eggs. Males (drones) are haploid, developing from unfertilised eggs through parthenogenesis. This unusual genetic setup creates the peculiar family relationships described in the Assertion.

    Let’s walk through the logic step by step.

    1. Why a male has no father.

       A drone develops from an unfertilised egg laid by the queen. That egg contains only the queen’s genetic material (haploid, $n$). There is no sperm involved, so there is no male parent. The drone’s entire genome comes from his mother. Hence, he has no father.

    2. Why a male cannot have sons.

       A drone produces sperm by mitosis (not meiosis), because he is already haploid. His sperm are all genetically identical to him. When he mates with a queen, the queen stores the sperm and uses it to fertilise eggs. A fertilised egg (diploid, $2n$) develops into a female — either a queen or a worker. An unfertilised egg (haploid, $n$) develops into a male. So the drone’s sperm can only contribute to producing female offspring. He cannot father a son, because a son would need to come from an unfertilised egg, which receives no sperm at all.

    3. Why a male can have a grandfather.

       Consider a drone. His mother is the queen. That queen is diploid and has a father — a drone who mated with her mother. So the original drone’s maternal grandfather is a drone from the previous generation. That grandfather is a male, and the original drone is his grandson. So yes, a male can have a grandfather.

    4. Why a male can have a grandson. …

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