Module 6.1: Reproduction Reproduction and Development
Reproduction
o a process by which individuals of a species are reproduced where
genetic material is passed from generation to generation.
o Animals and plants may reproduce either asexually or sexually
exclusively or they may alternate between the two modes
depending on environmental conditions.
o The changes that an organism undergoes from a zygote to an
adult involves growth and development.
Two types of Reproduction:
A. Asexual Reproduction - (Greek word means 'without sex')
process of producing offspring whereby only one parent is
involved.
B. Sexual Reproduction - creation of offspring by the fusion of
sperm and egg nuclei to form a zygote.
Module 6.2: Asexual Reproduction & Its Types Characteristics:
1. Genes comes from only one parent.
2. Offspring are genetical identical to the parents and to one
another.
3. No production of gametes
4. No fusion of gametes
5. Relies completely on mitotic cell division
Advantages of Asexual Reproduction:
1. It enables animal living in isolation to produce offspring without
finding mates.
2. Plants with desired characteristics can be cloned for economic
reasons.
3. Large number of offsprings can be produced in a short time.
4. It allows rapid colonization of the habitat.
Disadvantages of Sexual Reproduction:
1. The lack of genetic variability in asexually reproducing
populations can be detrimental when environmental conditions
change quickly.
2. Clones will gradually lose vigor.
3. It results to overcrowding and nutrient shortage
Types of Asexual Reproduction
1. Parthenogenesis - females produce eggs, but these develop until
young without ever being fertilized.
> Example; Fishes, several kinds of insects, few species of
frogs and lizards and some animals.
2. Sporulation - formation of spores that are microscopic and
unicellular , each containing cytoplasm and nucleus. Spores are
formed in spore-bearing structures called sporangia.
> Example: bacteria, fungi , mosses and ferns. In bacteria,
spores are also called endospores.
3. Budding - can be observed in unicellular and multicellular
organisms . Bud, is a formation of an outgrowth from the parent
organism. It gets separated from the parent by the formation of
a wall. It falls off and germinates in to a new individual.
> Examples: Hydra, yeast and Obelia
4. Binary Fission - a unicellular organism i nto two new identical
daughter cells through mitosis.
> Example: Amoeba and Paramecium
5. Regeneration - occurs when the parent body breaks into pieces,
each piece can grow into a new organism.
> Example: Planaria, sponges, starfish and filamentous
algae
6. Vegetative Propagation - production a new plant from vegetative
structures such as stem, leaf or root, of the parent plant. This
method is often used in order to keep particularly desirable traits
like flower color, fruit flavor, or resistance to disease.
Module 6.3: Sexual Reproduction & Its Types
Characteristics:
1. Both gametes are produced by Meiosis.
2. Gametes are haploid and differ in genetic composition.
3. Egg is typically large, non-motile and stores nutrients that
support the development of the embryo.
4. Sperm is usually small and motile. It propels itself by beating its
long, whip-like flagellum.
5. When sperm and egg are produced by the same individual, it is
known as hermaphrodite.
Advantages of Sexual Reproduction:
1. It increases genetic variability among offspring
2. During gamete production, crossing-over and the independent
assortment of chromosomes occur, resulting in offspring that are
genetically different.
3. Advantageous in a changing and unpredictable environment as
natural selection occur which leads to adaptation to the new
environment.
Disadvantages of Sexual Reproduction:
1. Rate of offspring production is relatively low
2. It require both male and female gametes which must meet for
reproduction to occur.
3. It produces both individuals that are well-adapted and
individuals that are less well-adapted to the environment. For the
less well-adapted, the death rate is high among offspring.
Two Types of Fertilization:
1. External Fertilization - mating partners usually release eggs and
sperm into the aquatic environment simultaneously . Gametes
can only live for a short time and many are lost or eaten by
predators. Thu s many gametes are released so that sufficient
numbers of sperm cells are able to fertilize egg cells.
> Example: Frogs and Fishes
2. Internal Fertilization - male delivers sperm cells directly into the
body of the female in a process called copulation. The fusion
occurs in body of the female.
> Example: terrestrial animals, sharks, aquatic reptiles,
birds, and mammals
Three strategies for embryonic and fetal development:
1. Oviparity - animals that lay eggs, embryos are nouri shed by the
egg yolk, shelled egg prevents embryo from drying out.
> Example: fish, amphibians, reptiles, birds, most insects
and arachnids
2. Ovoviviparity - fertililized eggs are retained within the mother to
complete their development. The young are fully developed
when they are hatched and released from their mother.
> Example: fish, many reptiles, water snakes and pit
vipers.
3. Viviparity - young develop within the mother and obtain
nourishment, directly from their mother's blood rather than the
egg yolk.
> Example : cartilaginous fish, some amphibians, few
reptiles and almost all mammals.
Module 6.4: The Human Male Reproductive System
Human Reproduction
o involves internal fertilization and integration action of the
endocrine and reproductive systems.
Gonads
o sex organs that produce gametes.
Testes (singular testis)
o male gonads, produce sperm and
male sex hormones.
