HSC Biology Module 5

Reproduction

Reproductive success

The ability to produce fertile offspring that survive to reproductive maturity and produce offspring of their own.

Biological fitness

the measure of an individual's reproductive success. It is calculated as the average contribution to the gene pool made by a certain genotype within a population and the relative likelihood that these alleles will be represented in future generation.

Sexual reproduction

It involves the meeting of special sex cells called gametes. A fertilised egg (zygote) occurs from the haploid gametes when the chromosome number changes from haploid to diploid.

Gametes

Carry genetic information from both parents, therefore the offspring with contain a mix of parental genes.

Diploid

(two complete sets)

Haploid

(single set)

Diploid and haploid cells

Refer to the number of sets of chromosomes within any cell - haploid (n) gamete from each parent combines to produce genetically unique diploid (2n) offspring.

Somatic cells

A term used to describe all body/non-reproductive cells.

Sexual reproduction in animals

The union of male and female gametes (sperm and ova) can occur outside the body (known as external) or inside the body (known as internal).

Hermaphrodites

When the animal has both male and female reproductive organs.

Internal fertilisation

Takes place inside the body of the female and involves mate attraction and compilation, which requires energy investment and put the organisms at risk of predation, but fewer eggs need to be produced. It occurs in some invertebrate and most vertebrates.

External fertilisation

Occurs in aquatic or moist terrestrial environments, to prevent dehydration of gametes, gametes must be produced in large numbers to ensure success. It occurs in most invertebrates and some vertebrates.

Artificial insemination (animals)

The process by which the sperm from a selected male with desirable traits is artificially transferred to the female.

Artificial insemination (animals) benfits

Used to inseminate a large number of females, transport of semen is easier than transporting of a whole animal, semen can be stored for a long time.

Artificial insemination (animals) limitations

Cannot guarantee 'favourable' traits to be passed on, reduced genetic variation; population susceptible to environmental changes.

Sexual reproduction in plants

Plants rely on external agents to carry the gametes from one parent to another, known as pollinating agents as well as external agents to disperse their seeds (wind, water, animals).

Anther (male - flower)

Where pollen grains are formed.

Filament (male - flower)

The stalk-like structure that attaches to the base of the flower and supports the anther.

Stigma (female - flower)

The sticky top surface of the flower in which pollen adhere too.

Style (female - flower)

Joins the stigma to the ovary.

Ovary (female - flower)

Where ovules is formed.

Pollination

The process of gamete transfer from the male gametes in the pollen to the female part of the flower, stigma from the anthers. Once the pollen has been deposited on the stigma, a pollen tube germinates and grows down the style, carrying inside it the male gamete to and ovule contained in the ovary.

Cross-pollination

The transfer of pollen from the anther of a flower of one plant to the stigma of the flower of another plant of the same species. It relies on outside agents to transfer pollen from anthers to stigma (wind or water).

Self-pollination

The pollination of a flower by pollen from the same flower or from another flower on the same plant. Self-pollination requires less energy.

Pollination by wind

The process of the transfer of pollen from one individual plant to another, whereby the pollen is carried by air currents (anemophily)

Pollination by animal

Involves the animal going from plant to plant, pollen grains stick to them and are deposited into the next flower. Animals can also help plant reproduction by dispersing seeds around in different areas.

Seed dispersal

The movement or transport of seeds away from the parent plant. The success of seed dispersal depends on the type of agent that the plant relies on.

Germination

The process by which an organism grows from a seed or similar structure.

Artificial pollination (plants)

The process by which pollen from a selected plant with desirable traits is artificially transferred to the female stigma of another plant.

Artificial pollination (plants) advantages

Used to pollinate many flowers (valuable in farming), a particularly useful and easy way of breeding new varieties of plants.

Artificial pollination (plants) limitations

Cannot guarantee 'favourable' trait is passed on, reduced genetic variation; populations more susceptible to the environment.

Asexual reproduction

Only one parent is required and all genetic material of the offspring is identical.

Asexual reproduction - plants

Vegetative popagation

Vegetative propagation

When a multicellular structure become detached from the parent plant and develop into new individuals that are genetically identical to the parent plant. Perennating organs are underground organs like roots or stems that contain enough stored food to sustain a plant in a dormant state.

Asexual reproduction - other organisms

Budding, spores

Spores

Tiny, unicellular reproductive cells that are produced in great numbers by organisms like fungi and plants - sporangia is what produces very large numbers of spores which are light and easily dispersed, traveling long distances in the wind.

Budding

When an adult organism gives rise to a small bud, which separates from the parent and grows into a new individual. i.e. yeast (a unicellular organism)

Examples of asexual reproduction

Plants:
- bulbs
- runners.

Animals:
- budding: coral
- regeneration and fragmentation: flatworms, sea sponges
- pathogenesis: honey bees, aphids, ants, stick insects.

Asexual reproduction advantages

Energy-efficient, required only one parent, no courtship required.

Asexual reproduction disadvantages

Low genetic diversity, more prone to environmental change, inhibits adaption.

Sexual reproduction advantages

High genetic diversity, less prone to environmental change, facilitates adaptations.

Sexual reproduction disadvantages

Energy costly, required two parents, courtship is time and resource communing.

Internal fertilisation advantages

Fertilisation more likely to occur, embryo protected from predators, offspring more likely to survive.

Internal fertilisation disadvantages

Higher energy requirement to find mate, less offspring produced, more energy required to raise and care for young.

External fertilisation advantages

Little energy required to mate, larger numbers of offspring produced, offspring can be spread widely; less competition.

External fertilisation disadvantages

Many gametes go unfertilised, offspring often not protected by parent; may die.

Bacteria (asexual reproduction)

Unicellular prokaryotic microorganisms produce asexually; binary fission.

Binary fission in bacteria: the steps

First cells elongate by building more cell wall, then the bacterial genome replicates and remains attached to the membrane. At the same time, any plasmids (small circular DNA) present replicate. Afterwards, they duplicated DNA begins to separate, moving towards the poles as the cell elongates and then cleavage furrow begins to form and cell wall form in cleavage furrow. Two identical daughter cells are produced.

Ways bacteria incorporates variation into genome

Conjugation, transformation, transduction.

Conjugation

Direct transfer of DNA from one bacterial cell to another.

Transformation

Nacked DNA is taken up from the environment by bacterial cells.

Transduction

The use of bacteriophage to transfer DNA between cells.

Fungi (primarily asexual reproduction)

Eukaryotic, unicellular or multicellular, heterotrophic.

Hyphae are the basic structural unit at fungi
Above ground = fruiting body
Below ground = mycelium

Reproduction methods; fragmentation, budding, spores.

They can produce spores sexually in response to adverse environmental conditions; homothallic or heterothallic.

Protists (both asexual and sexual reproduction)

Eukaryotic organisms which are neither true plants, animals or fungi.

Asexual reproductions methods: binary fission, multiple fission, budding.

Sexually reproducing protists; syngamy and conjugation.

Transgenesis

The process by which a gene is removed from one species and inserted into the genome of another species; it increases the genetic variation within a population.

Transgenesis - advantages

Guaranteed to express desired traits, increased yield and nutritional value, reduce the use of harmful chemicals.

Transgenesis - disadvantages

Offspring genetically identical - disease susceptibility, 'escape' of GMO into the wild population, trade issue with non-GMO countries, long term effects on human health are unknown.

Transgenesis in animals

GM Atlantic salmon have two genes from other species into their genome; these genes allow for the GM Atlantic salmon to grow all year round and grow 11 times faster than the average one.

Transgenesis in plants

Bacillus thuringiensis (Bt) is a bacteria species that produces a protein that is toxic to selective insect pests. This gene is isolated and inserted into cotton plants to produce a species called Bt cotton. The plant produces a 'natural' insecticide that kills pests as well as higher yield and reduction to use of harmful and expensive pesticides.

Fertilisation

Fusion of haploid male and female gametes.

Zygotes

Diploid cell resulting from the fusion of gametes.

Morula

Early stages of cell division.

Blastocyst

Inner cell mass will form the embryo, outer layer will form the placenta.

Implantation

The attachment of the blastocyst to the wall of the uterus.

Pregnancy

The state of carrying a developing embryo or fetus within the female body.

Embryo

Developing human from fertilisation to the eight week point.

Sperm

The smallest human cell; 50um, they cannot be seen by the naked eye. Fertile men ejaculate between 2-5mL of semen, 150 million sperm. The fastest swimmers find the egg within an hour. They are attracted by chemotaxis and thermotaxis.

Egg (ovum)

It is the production of eggs begin before birth. Each female is born with up to 2 million eggs, but by puberty one quarter remains. During each menstrual cycle several hundred eggs start to develop and mature, but only one egg typical reaches full maturity, the remaining are discarded and the dominant one released into the fallopian tubes during ovulation.

Fertilisation timeline

First, the sperm makes contact with the egg and burrows through the corona radiata. Then the sperm attaches to the receptor of zona pellucida. Digestive enzymes released (acrosome) and sperm burrow through zona pellucida. The plasma membranes of sperm and egg fuse and then the sperm nuclei enter the egg.

Hormones

A chemical substances that act as messengers in the body, coordinating many aspects of functioning, including metabolism, and reproduction.

Pituitary gland

An endocrine gland, attached to the base of the brain and just above the roof of the mouth. It secretes hormones that stimulate or inhibit other endocrine glands, regulating the release of their hormones.

Sex hormones

The hormones that specifically affect the growth and functioning of the reproductive organs or development of secondary sex characteristics. They are produced in special tissue in the ovaries and testes and in the pituitary gland and adrenal cortex.

Gonads

The are reproductive organs that become functional at puberty and the reproductive cycle commences. Gametes are produced in male and female gonads by a process known as gametogenesis.

Continuous breeding

Females fertility occurs in a cycle that is repeated all throughout the year and the animals are sexually activity all year round.

Hormonal involved in mammalian reproduction

Androgens, oestrogen, progestogen.

Seasonal breeding

Occurs only during periods of female fertility, commonly referred to as the animal being 'on heat' or 'in seasons' with the biological term being 'in oestrus'.

Androgens (male hormones).

It controls the development and functioning of male sex organs and secondary sex characteristics.

Oestrogen (female hormone).

The group control the development and functioning of the female reproductive system and secondary sex characteristics.

Progesterone (female hormone).

The most common progestogen and it plays a primary role in pregnancy. It also stimulates the secretion of milk in mammary glands and a drop in its levels plays a role in initiating menstruation.

Progesterone and oestrogen

They are produced by the ovaries and controlled by hormones of the pituitary regulate the ovarian cycle, menstrual cycle, maintenance of pregnancy, preparation for and maintenance of lactation and the pituitary secretes two gonadotropic hormones: follicle stimulating hormone (FSH) and luteinising hormone (LH).

Follicle stimulating hormone (FSH)

Secreted by the ovaries it initiates the ripping of the graffian follicle and ovum in the ovary and stimulates secretion of estrogen.

Luteinising hormone (LH)

Secreted in the pituitary gland it cause the follicle to release the ripe ovum (ovulation). Cause the empty graffian follicle to grow into a corpus luteum and inhibits secretion of estrogen.

Estrogen

Secreted in the ovaries, it contributes to the growth and development of the endometrium and maturing of the graffian follicle.

Progesterone

Secreted in the ovaries, it causes the endometrium to thicken and become highly vascularised (lots of blood vessels) and inhibit the release of FSH and LH.

Manipulation of reproduction in agriculture

Selective breeding, cloning, somatic cell transfer, artificial insemination.

Somatic cell transfer

Taking the embryo of an animal and implanting it to fuse with another to have all the traits of the two animals within the genes of the offspring.

Artificial insemination

Sperm is taken from the male animals, and when the female animal is ovulating the insert the sperm artificially into the cervix. It occurs without sexual reproduction. Embryo transfer can also occur, wherein vivo fertilisation occurs (allowing for offspring to have all desired genes). The embryos are then flushed, and the best are then implanted.

Embryo transfer

Invivo fertilisation occurs (allowing for offspring to have both desired genes). It involves the female taking hormone injections to produce multiple ovum, the sperm being injected into the female for fertilisation to occur. The embryos are then flushed, and the best are then implanted into a surget animal - known as IVF.

Selective breeding

Occurs in both plants and animals and involves picking the best traits for organisms to then insemination artificial to produce offspring

Hydrate - the product of intense selective breeding.
Hybrids vigour - show qualities superior to those of both parents.

Monoculture

A large area of genetically identical crops.

Cloning

The result of any asexual reproduction, were the offspring is identical to its parent. Plants do this through tissue scraping and mammals (animals and humans) do this through stem cells (somatic cell transfer).

Cloning (plants) advantages

All plants have the same advantageous features as the original plant, value is consistent, ripen at the same time, quality is consistent, genetic modification is easily replicated.

Cloning (plants) disadvantages

All are equally susceptible to the same diseases, all susceptible to the same pests, can strip the soil of nutrients, genetic diversity of the species is reduced.

Cloning (animals) advantages

Animals with the best traits can be replicated, the general quality of heards can be more rapidly improved, genetically modified animals can be replicated so no specialised genes are lost.

Cloning (animals) disadvantages

Genetic diversity decrease, cloned animals will all be equally susceptible to the same disease/parasites, hybrids vigour may be lost.

Reproductive technologies

Range from those that manipulate fertilisation like artificial insemination, IVF, artificial pollination to those that split up embryonic stem cells and involve embryo implantation like embryo splitting and cloning.

Cell cycle

G1 phase, S phase (synthesis), G2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis).

Mitosis

It is the cell division that produces two daughter cells that are genetically identical to parent cells (same number of chromosomes). It has five stages: prophase, metaphase, anaphase, telophase and interphase.

Ensures that every single cell contains the same genetic information which is necessary for the growth, repair and protein production.

Interphase (mitosis)

The cells are not dividing. Chromosomes are duplicating but not visibly.