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 (binary fission).
Parthenogenesis is development of an embryo from an unfertilised egg. In some birds (e.g. domestic turkey, rarely chickens) unfertilised eggs can develop parthenogenetically.
Parthenogenesis; example — domestic turkey (Meleagris gallopavo).
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 development of an embryo from an unfertilised egg. Examples: drones of honey bee (Apis), certain aphids; some whiptail lizards.
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.
They lack a segregated germ line and ageing process; successive binary fissions can continue indefinitely, so the lineage is theoretically immortal.
Asexual reproduction involves mitotic division without genetic recombination; hence progeny inherit the same genotype as the parent, constituting clones.
Because offspring are genetically identical to the parent (produced by mitosis), forming a group of genetically identical individuals called a clone.
(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.
Juvenile phase is the growth/maturation period when the organism is not sexually mature; reproductive phase begins after sexual maturity when gametogenesis and reproduction occur.
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.
Types of syngamy: isogamy, anisogamy and oogamy.