4.3 REPRODUCTIVE STRATEGIES AND TECHNOLOGIES
REPRODUCTIVE STRATEGIES IN AGIRCULTURE
-Controlled breeding of plants and animals with specific combinations of useful or desirable traits, this is called selective breeding
SELECTIVE BREEDING – process of breeding plants and animals for desirable traits
-Often imprecise because it combines many genes (therefore many traits) at one time
-Skillful and patient breeders have selectively bred many plants and animals
ARTIFICIAL INSEMINATION – process by which sperm are collected and concentrated before being introduced into the female’s reproductive system, artificial transfer of semen into a female’s reproductive tract
-Semen is processed and stored prior to introduction
-Most significant benefit of artificial insemination over more traditional methods is that it makes semen from high-quality males more widely available, through breeders and online sources
-Allows farmers and pet owners to choose desirable traits for the male parent
EMBRYO TRANSFER – the process by which an egg that has been fertilized artificially is transferred into a recipient female’s uterus
-Embryos can be shipped easily, eliminating the need to physically ship an animal from one place to another
-Studies show that animals born and raised in their native environment do better than those that are imported
REPRODUCTIVE TECHNOLOGIES FOR HUMANS
-Number of reproductive technologies now available for couples unable to conceive a child, techniques called Assisted Reproductive Technologies (ART)
-Artificial insemination used in humans, sperm collected and concentrated before being introduced into the woman’s vagina
-Donor sperm can be from woman’s male partner or from an unknown source (sperm bank)
IN VITRO FERTILIZATION (IVF) - technique used to fertilize egg cells outside the female’s body
-Women with blocked Fallopian tubes can use IVF
-Immature eggs retrieved and are combined with sperm in laboratory glassware (test tube babies, as fertilization occurs in laboratory glassware)
-After fertilization, developing embryo placed in uterus
-Variation of this method: injecting sperm into the egg where there is low or no penetration of the egg by sperm
-Louise Joy Brown, born July 25, 1978 is world’s first test tube baby
-Over 1.5 million babies conceived through IVF born since 1978
PREIMPLANTATION GENETIC DIAGNOSIS
-Parents who have history of genetic disorders in the family may choose to use a process that allows genetic disorder diagnosis after fertilization
-IVF is common, genetic testing done before embryo is implanted in the uterus, process is called preimplantation genetic diagnosis (PGD)
-Once IVF is performed, zygotes divide over 2 days and 1 cell from each of the developing embryos is analyzed for genetic disorders
-Healthy embryos are implanted in the female uterus
-Parents of sick children can use PGD to ‘engineer’ a genetic match in another sibling, newborn sibling is able to donate the umbilical cord blood which contains stem cells used to treat many diseases
-Further developments of IVF procedures continue to improve the success rate for human reproduction
-Ethical and social debates, wonder if people will find ways to abuse the technology and if there is a limit to how far we should go with them
CLONING: REPRODUCTIO OF EXACT COPIES
CLONING - process that produces identical copies of genes, cells or organisms
GENE CLONING
GENE CLONING – manipulation of DNA to produce multiple copies of a gene or another segment of DNA in foreign cells
-Cloned DNA can be used for further study, or mass production of the protein that the gene codes for
-Proteins produced this way have many commercial and medical applications
Ex. Insulin (enables body to use sugar) is absent in people with Type I diabetes
Before gene cloning, people used purified insulin from animal sources, but this was labour intensive ad expensive. Now human insulin is produced in bacteria through cloning the insulin gene
How to clone:
- - Isolate segment of DNA to clone, choose vector for cloning (vectors act as carriers of the DNA to be cloned so DNA can be copied in a foreign cell
- Commonly used vector for cloning in bacteria is called a plasmid (small circular pieces of DNA that remain distinct from the bacterial chromosome)
- – Insert chromosomal DNA into vector (relies on use of reagents that cut DNA and help different pieces join together)
-Resulting DNA molecule, which includes genetic material from different sources, called recombinant DNA
RECOMBINANT DNA – molecule of DNA that includes genetic material from different sources
- – Treat foreign cells such as bacterial cells so that they take in recombinant NDA
-Process of taking up recombinant DNA is called transformation
-Once recombinant DNA plasmid is taken into cell, many copies of the cloned gene or DNA fragment will be made by the host cell
THERAPEUTIC CLONING AND REPRODUCTIVE CLONING
THERAPEUTIC CLONING – process of replacing an egg cell’s nucleus with the nucleus from a somatic donor cell to produce a cell line of genetically identical cells
REPRODUCTIVE CLONING – process of producing genetically identical organisms
-Unlike gene cloning, therapeutic and reproductive cloning are surrounded by controversy because there are ethical questions about how they are used
-Both reproductive and therapeutic cloning use a process called somatic cell nuclear transfer (SCNT) to generate cloned cells
REPRODUCTIVE CLONING IN ANIMALS
-Reproductive cloning in animals is not very successful, birth rate only 0.5 – 6%
-Cloned offspring tend to have high mortality rates and high incidences of disease and premature aging
-Research into cloning animals continues because of potential applications such as repopulating endangered species
-First endangered animal clone in 2001, of an Asian gaur (rare ox-like mammal native to India/ Southeast Asia) from a dead gaur’s skin cells and fused with a domestic cow’s egg cells
-Egg transplanted into a surrogate domestic cow mother, cow successfully gave birth but cloned offspring died 2 days later
THERAPEUTIC CLONING AND STEM CELLS
STEM CELL – undifferentiated cell that can develop and become specialized into different cell types of the body
-Can develop into one of more than 200 types of somatic cells
-If human cells produced through SCNT are implanted into surrogate, they could develop into an embryo and produce a human clone
-Controversy due to initial use of embryos as source of stem cells
-Three different sources for stem cells:
- Embryonic stem cells – obtained from embryos
- Adult stem cells – somatic, retained ability to differentiate into some other cell types
- Induced pluripotent stem cells – specialized adult stem cells that have been induced to return to a stem-cell like state
-Reliance on embryonic tissue reduced/eliminated due to induced pluripotent stem cells
-Key to stem cell research is programming the stem cells to become certain cell types
-Stem cell research holds great promise for regenerative medicine to create tissues/ organs to replace damaged, old or defected ones
-Stem cells are generated from a patient’s own somatic cells thus are a genetic match, thus unlikely to be rejected by immune system
-Solves problem for tissue rejection and provides source of organs to supplement those already in short supply
TRANSGENIC ORGANISMS
-Researches developed techniques for inserting foreign DNA into plants/animals to create transgenic organisms whose genetic material include DNA from a different species
-GMO is an organism that has had the sequence of its genome altered for a specific purpose
APPLICATIONS OF TRANSGENIC PLANTS
-Modify to increase resistance to herbicides, insects, pests, viruses and increased nutritional value
-Rice is main staple food in developing countries, iron and vitamin A deficiencies affect many
-In 2000, Swiss researchers developed a genetically modified strain of rice called golden rice engineered to increase its vitamin A and iron content, thus golden rice is part of food air delivered to developing countries
-Transgenic plants used for medical purposes
Ex. Canadian company inserted human insulin gene into a safflower plant; transgenic safflower pant produces insulin as it grows, thus producing insulin this way is less expensive and makes diabetes treatment more affordable worldwide
APPLICATIONS OF TRANSGENIC ANIMALS
-Animals such as mice, fruit flies and roundworms widely used in research labs to study diseases and ways to treat them
-Transgenic milk producing animals are being used to produce medical protein products that include human growth hormones and anti-clotting factors
Ex. Canadian research company inserted spider genes into goats, transgenic goats secrete spider silk in their milk; goal of company is to eventually spin silk into lightweight strong fibres used for things such as clothing and nets
-Another area of research involves developing transgenic animals that can serve as organ donors for humans
-Transplanting organs from donor animals such as pigs has very little success due to tissue rejection
-Genetic engineering research teams conducing work to develop transgenic pigs that are more compatible with human tissues
-Research raises issues such as the risk of transferring diseases from pigs to humans
-Others ask if it is ethical to create new kinds of animals purple for the purpose of harvesting their organs
REGULATING THE USE OF TRANSENIC ORGANISMS
-Many organizations and citizen groups oppose use of transgenic organisms
-Risks include:
- Environmental threats: use of herbicide resistant plants could encourage use of stronger herbicides that may infect the water/soil system, Evidence that genes can cross to other species, creating superweeds or superbugs
- Heath effects: much is known about the long term effects of consuming transgenic products like food and medicine
- Social and economic issues: although beneficial to human health and reducing world hunger, amount of money spent on genetics research may be greater than overall benefit; private enterprises may have too much influence over global food market; others question the ethics of using other species solely for human benefit