Arrhenotoky is a form of parthenogenesis in which unfertilised eggs develop into males (haploid). Thelytoky produces females from unfertilised eggs, and amphitoky produces both sexes.
Bacterial 'sexual' process is conjugation — transfer of genetic material (plasmid or chromosomal fragment) between cells via a pilus. There are no true gametes; conjugation increases genetic variation (similar to sexual exchange).
Sexual reproduction produces variations due to meiosis (crossing over, independent assortment) and fusion of genetically different gametes (fertilisation), generating genetic recombination and diversity.
I: True. Honey bee males (drones) arise from unfertilised eggs (arrhenotoky) and are haploid; workers and queens are diploid—so R correctly explains A. II: True. Asexual reproduction involves mitotic divisions (no meiosis), producing genetically identical offspring (clones); R explains A.
In unicellular organisms like Amoeba (and bacteria), binary fission (cell division) is the method of reproduction — one cell divides mitotically into two daughter cells.
Amoeba is an organism where cell division itself serves as a mode of reproduction. In amoeba, the unicellular body undergoes binary fission, a form of asexual reproduction where the parent cell divides into two identical daughter cells. This process involves mitotic division of the nucleus followed by division of the cytoplasm, resulting in two genetically identical offspring. Binary fission is a simple and rapid method of reproduction that allows amoeba to increase its population quickly under favorable conditions.
Parthenogenesis is development of an embryo from an unfertilised egg. In some birds (e.g. domestic turkey, rarely chickens) unfertilised eggs can develop parthenogenetically.
The phenomenon where the female gamete directly develops into a new organism without fertilization is called parthenogenesis. An avian example is the domestic turkey (Meleagris gallopavo), where unfertilized eggs can develop into offspring. In this process, the haploid egg undergoes mitotic divisions to produce a diploid organism, bypassing the need for male gamete fusion. This form of asexual reproduction is particularly common in certain bird species and some other animals.
Parthenogenesis (a form of agamogenesis) produces offspring from unfertilised ova. Examples include honey bee males (arrhenotoky), many aphids, and some lizard species (e.g. whiptail lizards).
Parthenogenesis is the development of an embryo from an unfertilized egg without the fusion of male and female gametes. It is a form of asexual reproduction where the haploid egg undergoes mitotic divisions to produce a diploid organism. Examples of parthenogenesis in animals include drones (male bees) of the honey bee (Apis), where males develop from unfertilized eggs, certain aphids that reproduce parthenogenetically during favorable seasons, and some whiptail lizards (genus Aspidoscelis) where certain species reproduce entirely through parthenogenesis without males.
Sexual reproduction creates genetic diversity via meiosis and fertilisation, allowing adaptation and evolution — making it more effective in changing environments. Asexual reproduction (cloning) is efficient for rapid population growth in stable conditions but limits variability.
Sexual reproduction is more effective for long-term survival and evolution because it generates genetic variation; asexual reproduction is effective for rapid increase in stable environments.
Unicellular organisms (e.g. bacteria, Amoeba) divide by binary fission producing daughter cells identical to parent cell lineage. Because there is no distinct germ-soma separation and no organismal senescence, the lineage can continue indefinitely unless eliminated by external factors.
Unicellular organisms that reproduce by binary fission are considered immortal because they lack a segregated germ line and do not undergo an aging process in the traditional sense. When a unicellular organism like bacteria or amoeba divides by binary fission, each daughter cell is genetically identical to the parent and possesses the full genetic complement and cellular machinery. Since successive binary fissions can theoretically continue indefinitely under favorable conditions, the lineage never experiences senescence or death in the way multicellular organisms do. The genetic material is perpetually passed on through mitotic divisions without any loss of viability, making the cellular lineage theoretically immortal. This contrasts with multicellular organisms where aging and death are inevitable outcomes of their developmental program.
Asexual reproduction involves mitotic division without genetic recombination; hence progeny inherit the same genotype as the parent, constituting clones.
The offspring formed by asexual reproduction are referred to as clones because they are genetically identical to the parent organism and to each other. Asexual reproduction occurs through mitosis, which produces daughter cells with the exact same genetic information as the parent cell. Since no genetic recombination or variation occurs during mitotic division, all offspring are genetically uniform copies of the parent. A clone is defined as a group of genetically identical individuals derived from a single parent through asexual reproduction, making this term particularly appropriate for describing the products of asexual reproduction.
(a) Honey bee drones arise from unfertilised eggs (parthenogenesis), so the species exhibits parthenogenetic reproduction for males. (b) In haplodiploidy, males are haploid (single set of chromosomes) and females diploid (two sets); thus drone chromosome number is half that of female.
(a) Because males (drones) develop from unfertilised eggs (parthenogenesis/arrhenotoky). (b) Due to haplodiploidy: males are haploid (n = 16) from unfertilised eggs, females are diploid (2n = 32) from fertilised eggs.
(a) External fertilization occurs outside the body in water (e.g. fish, frog) with many gametes and low parental care; internal fertilization occurs inside the female body (e.g. mammals, birds) with fewer gametes and higher parental investment. (b) Lizards show limited/regional regeneration (tail autotomy, regrowth of cartilaginous tail with restricted tissues); planaria exhibit whole-body regeneration from small fragments owing to neoblasts (pluripotent stem cells) and can form complete individuals.
(a) External fertilization: gametes fuse outside body (aquatic animals, many fishes/amphibians), many small gametes, often large number of offspring and less parental care. Internal fertilization: gametes fuse inside body (terrestrial animals, mammals, birds), fewer gametes, greater parental care. (b) Regeneration: Lizard — limited regeneration (mainly tail) via blastema; replacement is partial and tissue types more restricted. Planaria — extensive regeneration: any small fragment can regenerate whole organism due to abundant pluripotent neoblasts.
Juvenile (pre-reproductive) phase involves growth, differentiation and somatic development under hormonal control; reproductive phase is characterised by sexual maturity, gamete production and ability to mate and produce offspring. Transition involves physiological and hormonal changes.
The juvenile phase and reproductive phase represent two distinct periods in the life cycle of an organism. The juvenile phase is the growth and maturation period during which the organism develops and increases in size and complexity, but is not yet sexually mature. During this phase, the organism cannot produce gametes and is incapable of reproduction. The reproductive phase begins after the organism attains sexual maturity, typically marked by the onset of puberty in animals. During the reproductive phase, gametogenesis (formation of gametes) occurs, and the organism is capable of sexual reproduction. The transition from juvenile to reproductive phase involves physiological and hormonal changes that enable the organism to produce functional gametes and participate in sexual reproduction.
Syngamy is fusion of two gametes. Major kinds: 1) Isogamy — fusion of morphologically similar gametes (both motile and same size); example: some algae (Chlamydomonas). 2) Anisogamy — fusion of dissimilar gametes differing in size/shape but both may be motile; example: some green algae/seaweeds. 3) Oogamy — extreme anisogamy with large non-motile egg and small motile sperm (typical of animals, higher plants); example: humans, many animals. (Optional note) Syngamy also occurs externally (external fertilisation) or internally (internal fertilisation) depending on site of gamete fusion.
Syngamy refers to the fusion of two gametes to form a zygote, and different types of syngamy are classified based on the morphology and motility of the fusing gametes. Isogamy is the fusion of two morphologically similar and equally motile gametes, as seen in many algae and fungi where both gametes appear identical. Anisogamy involves the fusion of two gametes that differ in size and morphology, where one gamete is larger and less motile than the other, observed in certain algae and protozoans. Oogamy is the fusion of a large, non-motile female gamete (ovum) with a small, motile male gamete (sperm), which is the most common type of syngamy in higher animals and plants. These different types of syngamy reflect variations in sexual reproduction strategies across different organisms.