Non-mammalian Reproduction

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What is Reproduction

Reproduction is the creation of a new individual or individuals from previously existing individuals. In animals, this can occur in two primary ways: through asexual reproduction and through sexual reproduction.

What is Asexual Reproduction?In asexual reproduction, one individual produces offspring that are genetically identical to itself. These offspring are produced by mitosis. There are many invertebrates, including sea stars and sea anemones for example, that produce by asexual reproduction.

In simpler term

What is the difference between Asexual reproduction and Sexual Reproduction

Advantages of Asexual reproductionLess Energy in reproductionLess Food in reproductionDon’t need two parents to occurDon’t need fusion of gametesMore offspring is produced in a small periodCommonly used by single-cellular organisms

Advantages of Sexual ReproductionMore pleasureAllows genetic variationUses fusion of gametesCommonly used by multi-cellular organismsRestoration of number of chromosomesAllows evolution

Disadvantages of Asexual ReproductionDon’t allows evolutionJust like cloningA negative mutation can make asexually produced organisms susceptible to disease and can destroy large numbers of offspring. Each clone may compete for foodUnfavourable condition may wipe all the organisms

Disadvantages of Sexual ReproductionNeeds two parents to reproduceMore energy and food in reproducingOnly 50% of the DNA of a parent is sharedTakes longer time to reproduceOther insects that reproduce sexually ends up in eating the male parent like the praying mantis and the black widow

Different Kinds of Asexual ReproductionBuddingGemmules(Internal Buds)FragmentationRegenerationParthenogenesisSpore FormationFission

BuddingIn this form of asexual reproduction, an

offspring grows out of the body of the parent. A small part of the parents body separates from the rest and develops into a new individual.

Example:◦ In hydra budding initially starts with a small bud

formed on the lower side of the body. This bud enlarges and develops tentacles. The tentacles help in feeding the daughter/small bud. The daughter bud eventually breaks off, from the parent body.

◦ In corals the buds do not detach from their parent body. They remain attached to the main body to form big colonies and help in collecting food.

Gemmule(Internal Bud)In this form of asexual reproduction, a

parent releases a specialized mass of cells from their bodies that can develop into offspring.

Example:◦Sponges also reproduce by means of

budding, along with gemmule reproduction. These cells develop into independent offsprings later on. The sponges reproduce by means of gemmules and other species reproduce using external bud.

FragmentationIn this type of reproduction, the body

of the parent breaks into distinct pieces, each of which can produce an offspring.

Example:◦Planarians/Flat worms is using

fragmentation as a means of reproduction. The flatworms divide in two piece which is called fragments that can grow into a new individual that can undergo into fragmentation after a long time

RegenerationIn regeneration, if a piece of a parent is

detached, it can grow and develop into a completely new individual.

Example:◦Hydra and Planarian may multiply by

regeneration. Sponges too have a tremendous power of regeneration. Ribbon-worms can get fragmented and each fragment can develop into a new worm. Starfish can regenerate its lost arm or the entire organism. Wall lizard can regenerate its lost tail.

Parthenogenesis Eggs produced by females develop into adult individuals

without getting fertilized. Some of the fishes, frogs and insects reproduce by means of parthenogenesis. In some organisms, parthenogenesis occurs under specific conditions. For example, when aphids get enough food to eat in the spring season, they resort to asexual reproduction because, it is a quicker means of producing offspring. However, these creatures also undergo sexual reproduction. Animals like most kinds of wasps, bees, and ants that have no sex chromosomes reproduce by this process. Some reptiles and fish are also capable of reproducing in this manner.

Example:◦ Honeybees, the female or queen honeybee is inseminated just once in

her lifetime. The sperm she receives are stored in a little pouch connected to the genital tract, and closed off by a muscular valve. As the queen lays eggs, she can either open this valve permitting sperm to fertilize them (to become female queens or female workers), or she can keep the valve closed so that unfertilised develop into male drones.

Spore FormationIt is one of the important and very efficient

methods of asexual reproduction in almost all groups of organisms except gymnosperms and angiosperms and animals. In bacteria, algae and fungi there are different types of spore-producing structures usually called the sporangia The small uni- or multinucleate spores are produced in large numbers in these spore-producing bodies during favourable conditions e.g., humidity, temperature and oxygen etc. After the rupture of sporangium the spores are released. They germinate on the suitable substratum to produce new individuals. Spores are of different types in different organisms.

Fissionoccurs when a cell simply grows larger, replicates

its DNA in genes and chromosomes, and then forms a cell membrane down the mid-section of the cell to form 2 new 'daughter' cells.

Formation of two identical daughter cells by the division of a protoplast by a constriction of its cell envelope is binary fission. The dividing cell grows in size; its genetic material (DNA) replicates first and the two molecules then separate. The genetic material along with the cytoplasm is distributed almost equally in two regions before the formation of two new cells as a result of a constriction of the cell membrane. It is the effective method of rapid multiplication.

Sexual Reproduction

FertilizationUnification of sperm and eggHas 2 types:

1. External2. Internal

Terms to rememberGonads: organs that produce

gametesCloaca: common oopening of

digestive, excretory and reproductive systems

Fertilization: Unification of sperm and egg; has 2 types:1. External2. Internal

Terms to rememberGametes: [haploid] the sperm

(spermatozoon, from male) and egg (ovum, from female) released during sexual reproduction

Zygote: [diploid] resulting cell formed from the fusion of a sperm and an egg

Internal FertilizationCooperative behavior (most of

the time there is courtship of male to female)

Animals with this have more complex reproductive systems

Copulatory organs to deliver sperm

Receptacles for sperm storage and egg transportation

Fewer but more protected gametes

External FertilizationOccurs mostly in moist habitatsThe environment signals

(stimulus) when gametes will be released, using chemical messages known as pheromones

A lot of zygotes are produced, but many die

Reproductive CyclesMost animals have definite cyclesSome animals reproduce both

sexually and asexually, switching when it is favorable for either method

Asexual reproduction occurs in favorable conditions while sexual reproduction occurs during crises

Reproductive CyclesHermaphrodites – have both

male and female sexual organsThere are organisms known as

sequential hermaphrodites◦Protogynous (f)◦Protandrous (m)