Plant Reproduction and Development

• Lecture brief on BIO101: General Biology 1 (2CUs) for the Department of Biology, Faculty of Science, at the Federal University Lokoja.

General Reproduction

• Reproduction is how living organisms create offspring, ensuring their species continues.

Reproduction in Plants

• Plant reproduction allows plants to create new members of their species to ensure continuity either sexually or asexually.

Sexual Reproduction in Plants

• Progeny results from the fusion of two haploid cells called gametes, produced by meiosis and fusing to create a diploid zygote.
• Syngamy is the union of gametes, a process known as fertilization.
• Flowers are the reproductive organs, specialized shoots of limited growth.
• A flower develops on a receptacle, floral parts arranged in whorls:
  • Calyx (sepals) protect inner whorls as buds.
  • Corolla (petals) attract pollinators with bright colors.
  • Androecium (stamen): the male organ, consisting of a stalk (filament) and head (anther) containing pollen grains.
  • Gynoecium (pistil): the female organ, with a style, stigma, ovary, and ovule containing an egg cell.

Asexual Reproduction in Plants

• Asexual reproduction does not involve gametes or two organisms; one parent produces offspring through fission, fragmentation, spore formation, or vegetative propagation.
• Spore formation: unicellular bodies formed by cell division that germinate into new individuals under favorable conditions.
  • Fungi are known to reproduce through spores
• Fission: Organism divides into two (binary fission) or more equal-sized parts; binary fission is common in bacteria.
• Vegetative propagation: Parts of a plant detach and develop into independent individuals
  • Rhizomes (horizontal underground stems) are used in propagating plants like spear grass and ginger.
  • Detached leaves (Begonia, Bryophyllum) also take root
  • Cassava stem cuttings are used to grow new plants.
• Fragmentation: An organism breaks into two or more pieces, each regenerating into a new individual
  • Fragmentation is seen in filamentous algae, and in Fungi via hyphae fragmentation.

Reproduction in Animals

• Animals can reproduce asexually or sexually, each having advantages and disadvantages.

Asexual Reproduction in Animals

• This occurs in many eukaryotic, single and multi-celled organisms.
• Offspring are genetically identical to the parent.
• A single individual can produce offspring, and numerous offspring can be produced quickly.
• Fission/Binary Fission: Invertebrates reproduce by splitting into two parts and regenerating the missing parts, seen in planarians (flatworms).
• Budding: Part of the body grows and separates to form two individuals, one smaller
  • Budding is common in invertebrates like hydras and corals. In hydra, the bud develops into an adult.
• Fragmentation: An organism breaks into parts followed by regeneration.
• If the animal is capable of fragmentation, separate individuals can regrow from each part
• Observed in sponges and echinoderms
• In sea stars, a new individual regenerates from a broken arm with a piece of the central disc.
• Parthenogenesis: An egg develops without fertilization, resulting in haploid or diploid offspring based on the species.
  • It happens in invertebrates like water fleas, aphids, stick insects, ants, wasps, and bees.
  • Ants, bees, and wasps produce haploid males (drones).
• Some vertebrate animals such as certain reptiles, amphibians, and fish also reproduce through parthenogenesis.

Sexual Reproduction in Animals

• It creates a new organism that combines genetic material from two organisms, beginning with meiosis, which is a specialized cell division.
• Each parent contributes half the offspring's genetic makeup by creating haploid gametes.
• Diploid mother cells divide to produce haploid gametes via meiosis.
• Fertilization is the fusion of a sperm and an egg
  • Can occur inside (internal fertilization) or outside (external fertilization).
  • External fertilization occurs mostly in aquatic environments where both eggs and sperm are released into the water.
  • Internal fertilization occurs in terrestrial animals, and some aquatic animals,
  • May occur by sperm deposition in the female during mating, or by male depositing sperm in the environment for female pickup.
• Following internal fertilization, offspring are produced in three ways:
  • Oviparous: fertilized egg laid outside the female's body in a hard shell, seen in birds, some bony fishes, reptiles, amphibians, and few mammals (platypus and echidna).
  • Ovoviparous: fertilized eggs retained in the female's body until they hatch, which occurs in sharks, lizards, snakes, and some invertebrates (Madagascar hissing cockroach).
  • Viviparous: offspring are born alive after obtaining nourishment from the female mammary gland, occurring in most mammals, some cartilaginous fish, and a few reptiles.

Hereditary

• Hereditary is the study of how characteristics transmit from parents to offspring.
• Hereditary is defined as the transmission and expression of traits in an organism from parents to offspring, from structures called chromosomes.
• Only traits constituting the genetic makeup of parents are transmittable and expressible in offspring.
• Examples are skin color, eye color, hair color/texture, body size, head shape, ear shape, mouth shape, lip shape, nose shape, hand/leg length, neck length, blood grouping, baldness, tongue rolling, and, in plants, leaf/shoot color/shape, seed size/shape, flower color, fruit size, pigmentation.

Mendelian Laws of Genetics

• Gregor Mendel (1822 – 1884) was a monk in Austria known as the Father of Genetics because his work formed the foundation for the study of heredity and variation.
• He worked with Garden Pea (Pisum sativum).
• Peas are self-pollinating and can be cross-pollinated.
• They have a short life span.
• Mendel crossed pure bred short plants with pure bred tall plants.
  • Seeds from this cross all produced tall plants, meaning the short trait was suppressed by, and recessive to, the dominant tall trait.
• Mendel called the resulting plants the first Filial Generation (F1).
• Mendel's discoveries led to two laws:
• Law of segregation states that genes determine individual development and independently transmit from generation to generation without undergoing any alteration.
• Law of independent assortment states that when multiple factors are considered, each character behaves independently and inherits separately.

Evolution

• Evolution refers to gradual changes organisms undergo in response to environmental change.
• The theory gained acceptance after Charles Darwin published "The Origin of Species" in 1858 with evidence of the theory and possible mechanisms.

Lamarck’s Theory of Evolution

• Proposed in 1801 by Jean-Baptist Lamarck.
• Theory of Need: Use or disuse of a part or organ of the organism.
  • Early snake ancestors stretched their bodies to crawl in narrow spaces/dense vegetation, leading to body elongation.
  • Organs that become well-developed achieve.
• Become functionless/disappear with disuse.
• Theory of Acquired Characteristics of Inheritance: Structures or variations acquired are transmitted to the next generation.
  • Modern giraffes evolved from short-necked/legged individuals to stretch their necks/legs to reach leaves due to competition for low grasses.
  • Ducks originally had no webs between their toes, but as they continue frequently visiting water for food therefore the need to develop webs for swimming become a necessity and thus pass it on to their offspring

Darwin's Theory of Evolution

• Charles Darwin proposed organic evolution by natural selection in 1859:
  • All living organisms overproduce offspring.
  • Struggle for existence: Overpopulation leads to compete for existence.
  • Offspring show variation: No copies are alike.
  • Adaptive characteristics: Some offspring are well-adapted to survive the competition.
• Inheritance of adaptive characteristics: The fittest transmit variations to offspring, with poor adaptations dying off (extinction).
• Development of new species: Accumulation of favorable variations leads to divergence from the stock of the parents resulting in the formation of new species.

Key Genetic Terminologies

• Gene: Physical unit of inheritance transmitted through generations
• Chromosomes: Strands of genetic material found in the nucleus, containing DNA and protein.
• Character or Trait: Inheritable attributes or features possessed by an organism.
• Phenotype: Total observable features (physical, physiological, behavioral).
• Genotype: Term to describe the sum total of genes that form the genetic material of an individual.
• Dominant Character: A characteristic that is fully expressed in an offspring.
• Recessive Character: A trait masked or does not produce effect in the presence of a trait
• Homozygous: An individual with identical alleles for a trait (TT or tt).
• Heterozygous: An individual with two different alleles for a trait (Tt or Rr).
• Hybrid: the result of generically different parents
• Locus: The site for gene location on a chromosome.
• Haploid: An organism with one set of chromosomes in the reproductive cell, represented by (n).
• Diploid: An organism with two sets of chromosomes in the body cell, represented by (2n).
• Mutation: Change in an organism's genetic makeup, creating a new inheritable characteristic.

Explore plant reproduction, covering floral parts, pollination, fertilization, and asexual reproduction methods. Understand the roles of structures like the calyx, androecium, and gynoecium. Learn about spores, binary fission, rhizomes, and fragmentation.