Human intervention in evolution

Chapter 16

Phenotypic level:• Selective breeding• Reproductive technologies– Artificial insemination (in animals)– Artificial pollination (in plants)– Embryo transfer– Sex selection through sperm sorting

Genotypic level:• Transgenic organisms

Selective breeding• Selective breeding is the deliberate selection by a

breeder of individual plants or animals to provide the genetic material for the next generation

• Artificial selection occurs when breeders favour particular inherited features in their livestock and use selective breeding to enhance those features

• Unlike natural selection, the traits selected in this type of breeding may not be positively selected in the wild

• Loss of genetic variability

Reproductive technologies• Artificial insemination (AI)• Sex selection through sperm sorting• Multiple ovulation and embryo transfer• Oestrus synchronisation

Artificial insemination• AI involves collecting semen from a selected

stud animal and then introducing this semen by artificial means into the reproductive tract of females of the same species

• Freezing of semen was introduced in 1949 this means one prize stud animal can:– Fertilise many more

females than naturally– Fertilise females located

far far away– Fertilise females long

after it‘s dead

Embryo transfer in livestock (MOET)• Allows high quality ewes to makes a much greater

contribution to the future generations• Multiple ovulation: female receives injections of

FSH that stimulate her to super-ovulate (produce multiple eggs)

• Embryo transfer: embryos at day 6/7 are inserted into surrogate mother

• Embryos can be frozen

Sex selectinon through sperm sorting

• Treat semen to seperate X & Y chromosomes• Sperm cells are labelled with fluorescent dye– X chromosomes larger so fluorescent more brightly

Manipulating breeding cycles• Oestrus (part of sex cycle when female is ready to mate)• Oestrus synchronisation results in sexually mature females being in oestrus for a very specific

timeframe• Less time wasted• Higher fertilisation rates and birth rates

• Progestrone (stops production of Oestrogen)• Feeding diety supplement• Implants under skin• Sponges inserted into vagina• CIDRs (controlled internal drug releasing devices inserted into vagina

Artificial pollination in plants• Process involves:

– Removal of unripe stamens from the plant to be fertilised– Protection of the stigma of the selected female plant from stray

pollen– Collection of pollen to be used in artifical pollination– Transfer of donor pollen onto the stigma of female parent

• AP is used to create new plant species (wheat-rye hybrid) see p. 628

Cloning

• Creating genetically identical copies of an organism

• There are two ways:– Embryo splitting– Nuclear transfer

Transfering genes between species• Any organisms with „foreign“ DNA is a transgenic organism

(TGO)• This introduction and incorporation of external DNA can result

in permanent genetic changes– Prokaryotic cells (bacteria): Transformed– Eukaryotic cells : Transfected

• Techniques for gene transfer:– Micro-injection of the DNA of a gene into a cell– Transfer using a virus (retrovirus or adenovirus)– Use of an electric pulse– Use of ballistics (gene gun)– Cloned transgenic mammals (Polly) (case studies p. 638)

Gene therapy

• See chapter 4• Faulty allele in an organism is replace by the

normally functioning allele of the gene• Directly targets genotype• Gene therapy is still in its first stage with

clinical trials occuring in various institues (p. 639)

• Read blue box on p. 640

Stem cells: a new approach

• Stem cells are undifferentiated (precursor cells) that have the ability to differentiate into many different and specialised cell types

• Totipotent: give rise to all cell types• Pluripotent: give rise to most cell types• Mulitpotent: give rise to certain cell types

• Two different stem cell types:– Embryonic stem cells (obtained from blastocyst)– Adult stem cells (Somatic stem cells) (bone marrow, skin etc)

Stem cells: therapeutic cloning

• Nuclear transfer technique

• Ethical issues– Australia: use of excess embryos allowed

Technology in human reproduction

• Stopping conception• Overcoming infertility– Donor insemination– IVF (in vitro ferilisation) BIOTECH p. 648

– Donatino of eggs– Surogacy– Gamete intrafallopian transfer (GIFT)– Intracytoplamis sperm injection