Artificial selection (4)

Question 1

For thousands of years, farmers and breeders have used the variation in wild and cultivated organisms to develop their crops and to create new breeds of livestock by what is termed ____ ___.

Answer 1

artificial selection

Question 2

What is artificial selection?

Answer 2

Artificial selection is the process of selecting and breeding organisms with desirable characteristics to produce offspring with those characteristics that will be of some use to humans, e.g. horticulture, agriculture, transport, companionship and leisure. Artificial selection mimics natural selection.

Question 3

The selection process is simple; only those organisms with the ___ trait are allowed to reproduce.

Answer 3

desired

Question 4

Artificial selection, guided by humans and based on an understanding of genetics and reproduction, is an artificial version of ____ _____ and evolution, which is directed by nature.

Answer 4

natural selection

Question 5

What are the differences between artificial and natural selection in terms of processes?

Answer 5

Artificial selection: artificially via human choice

Natural selection: naturally via environmental selective agents

Question 6

What are the differences between artificial and natural selection in terms of who drives the processes?

Answer 6

Artificial selection: man

Natural selection: nature

Question 7

What are the differences between artificial and natural selection in terms of rate of change?

Answer 7

Artificial selection: fast

Natural selection: slow

Question 8

What are the differences between artificial and natural selection in terms of amount of variation?

Answer 8

Artificial selection: less variation

Natural selection: much variation

Question 9

What are the differences between artificial and natural selection in terms of consequence?

Answer 9

Artificial selection: improved crops and livestock

Natural selection: adaptation to environment

Question 10

What is the importance of artificial selection? The importance of artificial selection is that over time it has enabled farmers and breeders to: (9)

Answer 10

• domesticate wild plants (into uniform and predictable plants, e.g. wheat, maize and rice) and animals (for higher milk, meat and wool production, e.g. cattle and sheep).
• produce organisms that are resistant to pests and diseases.
• improve the quality and yield of crops, e.g. there has been an approximate 50% improvement in the major cereal crop yield since 1930.
• produce new strains of crops, e.g. ‘new’ vegetables such as broccoli and Brussels sprouts.
• produce new hybrid crops, often called high-yielding varieties (HYVs), to meet the ever increasing demands of human population.
• adapt old crops to enable them to grow in inhospitable climates or areas, e.g. where there are environmental pressures such as salinity, extreme temperature or drought. This will become more important as the effects of climate change are felt as a result of global warming.
• develop special breeds for particular purposes, e.g. dogs that herd sheep.
• enhance the nutritional value and flavour of fruits and vegetables.
• develop characteristics that are useful for storage, shipping and processing of foods.

Question 11

What is inbreeding?

Answer 11

Inbreeding is the mating of closely related individuals

Question 12

What are examples of inbreeding? (2)

Answer 12

• An extreme example is self-fertilization, e.g. wheat species.
• A more common example is the crossing of offspring of the same parents, e.g. highly pedigreed dogs.

Question 13

What is the function of inbreeding?

Answer 13

The function of inbreeding is to select and continue particular characteristics. However, it often leads to loss of vigour and poor survival as the offspring can become homozygous for a higher proportion of undesirable recessive genes.

Question 14

What is outbreeding?

Answer 14

Outbreeding is the mating of individuals not closely related, e.g. mongrel dogs arise in this way.

Question 15

What is the result of outbreeding?

Answer 15

The resultant offspring of outbreeding are tougher and more fertile with a greater chance of survival. The reason for this is that the offspring are probably heterozygous with undesirable recessive alleles being masked by normal dominant alleles.

Question 16

The different varieties of the dog, __ ______,are a striking example of artificial selection. The gene pool of dogs, 78 chromosomes (39 pairs) has a large amount of hidden genetic variability, which can be expressed under selective forces.

Answer 16

Canis familiaris

Question 17

What is a gene pool?

Answer 17

the total of all alleles of genes carried by all individuals in an interbreeding population

Question 18

The Grey wolf, Canis lupus is thought to have been the common ancestor to modern wolves and the dog species. The dog was the first species to be domesticated around 14 000 years ago. What traits were selected?

Answer 18

• Initially the traits selected for breeding were behavioural traits such as tameness, least aggressive, playfulness, subservience and being easy to work with.
• Later structural as well as behavioural traits were selected to produce dog breeds:
-for specific purposes, e.g. hunting (good sense of smell), guarding (aggression, strength), racing (lithe, strong build), and herding (agility, stamina).
- for domestic pets to provide affection and companionship, e.g. Maltese poodle (small size).

Question 19

Breeding by artificial selective over the centuries has produced the enormous variation seen in today’s dog populations: more than __ breeds.

Answer 19

350

Question 20

Of the approximate _____ species of edible plants _____ are used for food by humans. ____ percent of the world’s food comes from only 15 species with cereals (wheat, maize and rice) making up two thirds of this amount. Today, all our principal food crops come from domesticated varieties.

Answer 20

75 000
7 000
Ninety

Question 21

What has domestication of wild plants resulted in?

Answer 21

Domestication of wild plants has resulted in great phenotypic changes (and altered genotypes) and the development of new varieties. All of these domesticated plants are dependent on humans to preserve them. They are called cultigens to show their dependence on cultivation.

Question 22

The practice of domestication is estimated to date back _____ to ____ years.

Answer 22

9000

11000

Question 23

What artificial selection methods are used in plant breeding?

Answer 23

There are two methods – classical and modern.

Question 24

What does classic plant breeding involve?

Answer 24

Classical plant breeding uses deliberate interbreeding (crossing) of closely or distantly related individuals of a species to produce new crop varieties with desirable characteristics. For example, a mildew-resistant pea may be crossed with a high-yielding but susceptible pea, the purpose of the cross being to introduce mildew resistance without losing the high-yield characteristics.

Question 25

What does modern plant breeding involve? (4)

Answer 25

• genetic engineering
• Mutagenesis
• embryo rescue
• polyploidy

Question 26

What is genetic engineering? (2)

Answer 26

 select and transfer desirable characteristics from one plant to another, or
 to change the genetic material to produce more desirable characteristics.

Question 27

What is mutagenesis?

Answer 27

which is the production, by chemicals or radiation, of mutants that may have desirable characteristics.

Question 28

What is embryo rescue?

Answer 28

is the rescue of embryosfrom seeds of valuable plants, e.g. the seeds of some popular orchids do not have enough food reserves which results in too few seedlings being produced.

Question 29

About 10 000 years ago, early native Americans were able to change teosinte (Zea mays ssp. parviglumis), a wild grass into maize – the largest grain crop in the world. This transformation was not only the product of skilful breeding through artificial selection, but also as a result of the remarkable ____ ____ found in the teosinte.

Answer 29

genetic variation

Question 30

How did domestication of this crop occur?

Answer 30

Over the last thousand years farmers selected and planted seed from those teosinte plants with beneficial characteristics, while eliminating seed from those plants with undesirable features.

As a result, alleles of those genes controlling desirable characteristics increased in frequency within the population, while less desirable alleles decreased.

Eventually all seed produced from the favoured plants produced plants with the desirable characteristics.

Question 31

To achieve this dramatic transformation from teosinte, a multi-stemmed wild grass, into modern, upright Zea mays, many of the less common characteristics of teosinte had to be selected.

What phenotypic characteristics were selected? (4)

Answer 31

• Reduced covering of kernel (seed)
• Retention of kernels on the cob
• Erect habit with a single stalk
• Larger ear structure