Reproductive Technologies and Genetic Diversity

Breeding with a laboratory

For thousands of years, farmers improved crops and animals by selective breeding: choosing the best parents and letting nature do the rest. (Canola, one of Canada's most valuable crops, was developed by Canadian plant breeders in the 1970s this way.) Today, breeders also use reproductive technologies that let them choose parents from across the world, freeze genes for the future, copy an animal exactly, or move a gene from one species to another.

These tools are powerful, and they can change the genetic diversity of a species in either direction. The curriculum asks you to describe them and explain how they can increase diversity, so let's look at each one and keep track of its effect on the gene pool.

1. Artificial insemination (AI)

Semen is collected from a male, checked, often frozen in liquid nitrogen, and later placed in a female's reproductive tract. A large share of Canada's dairy cows are bred this way.

• Increases diversity: a farmer in Ontario can use semen from bulls in other provinces or other countries, bringing new alleles into the herd. Frozen semen from rare or old breeds can be stored for decades and used to bring back lost genetic lines.
• Can decrease diversity: if thousands of farmers all choose the same few popular bulls, many calves share the same father, and the gene pool narrows. Breeders track relatedness to avoid this.

2. In vitro fertilization (IVF) and embryo transfer

Eggs are collected from a female, fertilized with sperm in a lab dish, grown for a few days, and the embryos are transferred into a female's uterus (sometimes a surrogate). In livestock, one valuable cow can produce many more calves than she could carry herself. In humans, IVF helps people who have trouble conceiving; the first baby born through IVF, Louise Brown, was born in England in 1978.

• Increases diversity: combines eggs and sperm from parents who could never mate naturally (different continents, different times, using frozen embryos). Embryos of rare breeds can be frozen in gene banks.
• Can decrease diversity: if only a few elite females are used as egg donors.

3. Cloning

Plants have been cloned for centuries: every cutting, graft, or potato grown from a piece of potato is a clone. In tissue culture, thousands of genetically identical plantlets are grown from small pieces of a plant.

Animals can be cloned by somatic cell nuclear transfer (SCNT): the nucleus of a body cell is moved into an egg cell whose own nucleus has been removed. A small electric pulse starts division, and the embryo is placed in a surrogate. Dolly the sheep, born in 1996 at the Roslin Institute in Scotland, was the first mammal cloned from an adult body cell.

• Effect on diversity: cloning itself makes identical copies, so heavy use would reduce diversity. But it can rescue diversity: cells from rare or endangered animals can be frozen and cloned later. In 2020, a black-footed ferret named Elizabeth Ann was cloned in the United States from cells frozen in 1988, bringing genes back into a small endangered population.

4. Recombinant DNA and genetic engineering

Genetic engineering moves a specific gene into an organism. The basic toolkit:

1. Restriction enzymes cut DNA at specific sequences, often leaving short single-stranded sticky ends.
2. The same enzyme cuts a plasmid (a small ring of bacterial DNA), so the ends match.
3. DNA ligase seals the gene into the plasmid, making recombinant DNA.
4. The plasmid is put into bacteria (or, using other methods, into plant or animal cells). The cells now carry and use the new gene.

This works because all living things use the same genetic code: a human gene's instructions can be read by a bacterium.

• Increases diversity: genetic engineering can add completely new alleles or genes, even from other species, which selective breeding could never do.
• Concerns: if one engineered variety is planted everywhere, crop diversity can drop. Some people also raise questions about ecological effects, corporate control of seeds and labelling. You will weigh these questions in the ethics lesson.

Protecting diversity: gene banks

To keep options open for the future, countries store genetic diversity. Canada's national seed gene bank, Plant Gene Resources of Canada, is run by Agriculture and Agri-Food Canada in Saskatoon. Gene banks also store frozen semen and embryos of livestock breeds. These collections are insurance against disease, climate change and the loss of rare varieties.

Careers: animal geneticists, livestock breeders, AI technicians, embryologists, plant breeders, biotechnologists and genetic counsellors all work with these technologies.