U3 Plant and animal breeding

Question 1

what is plant and animal breeding used for?

Answer 1

to improve characteristics to help support sustainable food production

Question 2

What characteristics do breeders develop crops and animals with?

Answer 2

-higher food yields
-higher nutritional values
-pest and disease resistance
-ability to thrive in particular environmental conditions

Question 3

What is a plant field trial?

Answer 3

A type of investigation carried out in a range of environments to:

1-compare the performance of different plant cultivars (eg species a and species b) under the same set of experimental conditions

2-Find out the effect of different environmental conditions (treatments) on a new cultivar of crop plant

3-evaluate GM crops (conventional v GM crop)

Question 4

Once you have decided what is to be investigated in the plant field trial, what factors must be considered?

Answer 4

1-selection of treatments to be used (validity)
2-number of replicants to be included (reliability)
3-randomisation of treatments (eliminate bias)

Question 5

What is the reason for carrying out these procedures used in plant field trials?
1-Selection of treatments
2-number of replicates
3-randomisation of treatments

Answer 5

1-to ensure fair/valid comparison

2-to take account of the variability within a sample (experimental error)

3-to eliminate bias when measuring treatment effect

Question 6

What does outbreeding involve?

Answer 6

the fusion of 2 gametes from unrelated members of the same species

Question 7

What does inbreeding involve?

Answer 7

The fusion of 2 gametes from close relatives.

Question 8

In what organisms is inbreeding naturally occurring?

Answer 8

In some species of self-pollination plants eg peas, what and rice

They are also less susceptible to inbreeding depression due to the elimination of deleterious alleles by natural selection

Question 9

What does inbreeding ensure?

Answer 9

That the members of each generation of a selectively bred strain receive alleles for the desired characteristic

Question 10

What can inbreeding lead to?

Answer 10

loss of heterozygosity

inbreeding depression

Question 11

What is loss of heterozygosity?

Answer 11

Continuous inbreeding leads to loss of heterozygosity and development of homozygous

(ie the frequency of heterozygous individuals in a population decreases. There will be less heterozygous individuals and more homozygous individuals)

Question 12

What is inbreeding depression?

Answer 12

If a natural outbreeded is forced to inbreed, inbreeding depression can occur

This is due to the accumulation of homozygous recessive alleles which can be deleterious

(normally t natural selection would select against the weaker recessive phenotype)

Question 13

What does inbreeding depression appear as?

Answer 13

a decline in vigour, size, fertility and yield of the plant or animal

Question 14

What does vigour and deleterious mean?

Answer 14

vigour-strength
deleterious-harmful

Question 15

Inbreeding summary

Answer 15

• In inbreeding, selected related plants or animals are bred for several generations until the population breeds true to the desired type due to the elimination of heterozygotes.

• A result of inbreeding can be an increase in the frequency of individuals who are homozygous for
recessive deleterious alleles. These individuals will do less well at surviving to reproduce. This results in inbreeding depression

Question 16

Why is inbreeding rarely carried out indefinitely?

Answer 16

Due to the problems associated with inbreeding depression

Question 17

What is used instead of inbreeding in animals?

Answer 17

New alleles are introduced by crossbreeding individuals from different breeds

This can produce a new crossbreed population that have improved characteristice

Question 18

How are new alleles introduced to plant and animal lines?

Answer 18

By crossing a cultivar or breed with an individual with different desired genotype

The 2 parent breeds can be maintained to produce more crossbred animals showing improved characteristics

Question 19

In plants, how are F1 hybrids produced?

Answer 19

by crossing (hybridisation) of 2 different inbred homozygous cultivars

This creates a relatively uniform heterozygous crop

Question 20

What do F1 hybrids display?

Answer 20

increased vigour and yield

Increased vigour may mean increased growth rate and disease resistance

poorer recessive genes are masked by superior dominant ones

Question 21

Why are F1s better?

Answer 21

If desirable F1 hybrids are allowed to interbreed with one another, the F2 generation can be too genetically diverse and many will lack the improved characteristic seen in F1

Question 22

How can plants and animals be enhanced using genetic technologies?

Answer 22

1-genetic sequencing (we studied this more in unit 1)
2-genetic transformation (we studied this more in unit 2)

Question 23

What is genetic sequencing?

Answer 23

Genome sequencing techniques can be used to identify organisms that possess particular alleles for a desired characteristic

This organism can then be selected for use in a breeding programme

Question 24

What is genetic transformation?

Answer 24

(genetic engineering)

Breeding programmes can involve crop plants that have been genetically modified using recombinant DNA technology

Single genes for desirable characteristics can be inserted into the genomes of crop plants, creating genetically modified plants with improved characteristics. These can then be used in a breeding programme.