Human intervention in evolution Chapter 16 – Part 1

Selective Breeding Selective breeding is the process of breeding plants and animals for particular genetic traits which are desirable. This is achieved in animals by using male animals with the desirable traits for a number of generations until the undesirable traits die out in the population.

Selective Breeding: Australian Sheep Selective breeding is an integral part of the Australian wool industry. Selective breeding has been used to increase the amount of wool a sheep produces and also to reduce the diameter of the wool fibres. Selective breeding among sheep is achieved by breeding ewes with rams that have the desired traits.

Selective Breeding: Australian Cattle Selective breeding has also been used with cattle in Australia in order to increase milk yields among dairy cows. The modern dairy cow can produce about litres of milk per day. This is about ten times more milk than a calf would ever need.

Reproductive technologies There are many reproductive technologies associated with selective breeding. This includes: Artificial Insemination (AI) Embryo transfer in livestock (MOET) Sex selection through sperm sorting Multiple ovulation and embryo transfer Oestrous synchronisation

Artificial Insemination (AI) Artificial Insemination involves collecting semen from a selected male and then introducing this into the reproductive tract of a female. The advantages of AI are A single volume of ejaculate from a male can be sufficient to fertilise a number of eggs. Female can be fertilised by sperm that has come from other regions and even other parts of the world. A male’s ejaculate can be used long after it has died.

Genetic Impact of AI in animal breeding By using semen samples from selected animals, genetic variability is reduced among populations. If random mating was allowed to occur, then a greater variety of traits would exist. The widespread use of AI could result in the loss of undesirable traits and also expose animals to a greater susceptibility to diseases that they would otherwise have built up a resistance against.

Embryo transfer in livestock (MOET) Multiple Ovulation and Embryo Transfer (MOET), allows more desirable females to contribute a greater amount of gametes. Multiple ovulation refers to the process where the female animal receives injections of follicle stimulating hormone (FSH) in order produce a greater amount of eggs when she ovulates. Embryo transfer involves transplanting fertilised embryos into surrogate mother.

Sex selection through sperm sorting In some agricultural industries, being able to select the sex of the offspring is an advantage for farmers. This can now be done by dying sperm with a fluorescent dye and separating out the sperm with X- chromosomes from the sperm with Y-chromosomes. This is especially important in the beef industry where males are preferred and also in the dairy industry where females are preferred.

Manipulating breeding cycles This involves the synchronisation of the oestrus cycles of female animals. NOTE: animals can only become pregnant if they are inseminated during oestrus. This is important for the MOET procedure (discussed earlier). It also allows for higher rates of fertilisation and births. The synchronisation of oestrus is achieved by the introduction of the hormone progesterone to the female. This can be introduced through: The animal’s diet Skin implants Vaginal implants Once the source of progesterone is removed, the animal begins oestrus within 3 days.

Artificial pollination in plants Artificial pollination has been used for centuries. This was the basis of Gregor Mendel’s pea experiments. This process involves: Removal of unripe stamens from plant to be fertilised. Protection of the stigma of the selected female plant from stray pollen. Collection of pollen Transfer of pollen to the stigma of the female plant.

Creating Hybrids Artificial pollination can be used to create hybrid plants. For example wheat and rye can be crossed together to create a hybrid (like a horse and donkey produces a mule). This hybrid is infertile.

Cloning Cloning is a form of asexual reproduction. This involves the genetic information required for a new individual originating from only one parent. There are different types of cloning techniques. For example: Cloning by embryo splitting Cloning by nuclear transfer

Embryo Splitting Embryo splitting involves removing an embryo from an individual. Individual cells from this embryo are removed and then placed into Petri dishes that contain the correct nutrients and hormones for growth. Each of the removed cells now divides to form a new embryo. These embryos are then implanted into the uterus of surrogate mothers. These surrogate mothers will then give birth to identical offspring.

Cloning using nuclear transfer techniques There are many different ways to manipulate cells and their nuclei. For example, you can: Remove the nucleus from a cell, enucleated. Transfer the nucleus from one cell to an enucleated cell. Fuse a somatic cell with an enucleated cell

Dolly the Sheep Dolly the sheep was created using a somatic cell from her mother and fusing this with an enucleated egg cell. Once the egg cell showed evidence of early embryonic development, it was transferred into the uterus of a surrogate animal.

Cloning: the downside Success rate of cloning is very low. Hundreds of embryos often need to be implanted into females in order to successfully end up with a growing embryo. Each time mammalian cells divide, the telomeres on the ends of chromosomes get shorter. It is thought that this is the cause of aging. So therefore cloned animals would age rapidly. This has been evidenced in Dolly the sheep. She had to be put down at age 6 because of lung problems and severe arthritis.

Cloning Plants This can be naturally or artificially done. Examples of natural cloning are: cuttings, runners, suckers, etc. Artificial cloning of plants involves the culturing of a piece of adult plant. This can then be divided further to create a large number of cloned copies of the plant. All of the resulting individuals are genetically identical.