Unit 3 KA2

Question 1

Selective breeding

Answer 1

The selection of desirable characteristics in crop plants and domesticated animals .

Improved characteristics create better animal breeds and crop cultivars, as a sustainable food source for humans.

Selected characteristics include yield, nutritional content, pest resistance etc.

Question 2

Field trials

Answer 2

Used to test the performance of new varieties of crop (cultivars) in the field.

Can be used to evaluate fertiliser requirements, environmental conditions, GM crops etc

Set up in the same way as an investigation with an aim, independent, dependent and controlled variables.

Question 3

Replicates

Answer 3

Repeat plots with identical conditions.

Used to ensure reliability of results and validity of the experiment, since it is hard to control all variables in the field.

Question 4

Randomisation

Answer 4

Replicate plots are mixed up, rather than being arranged in sequence, to reduce environmental bias.

Question 5

Discrete variation

Answer 5

Characteristics which are used to divide individuals into distinct groups. eg blood groups, tongue rolling

These characteristics (phenotypes) are controlled by a single gene, and can be investigated using monohybrid crosses.

Question 6

True breeding

Answer 6

Offspring are always identical to the parents for a particular characteristic, if homozygous parents are self-fertilised and inbred.

Question 7

Homozygous

Answer 7

Genotype where the 2 alleles are the same eg. BB, rr

Question 8

Heterozygous

Answer 8

Genotype where the 2 alleles are different, eg. Bb, Tt

Question 9

Test cross

Answer 9

An individual which carries a dominant gene could be BB or Bb - same phenotype, different genotype.

Cross with a homozygous recessive individual with an known genotype, in order to identify it.

Test crosses result in different phenotype ratios in the offspring, allowing the unknown parent to be identified.

Question 10

Outbreeding

Answer 10

The fusion of 2 gametes from unrelated members of the same species, leading to increased variation.

Most animals and plants are natural outbreeders.

Question 11

Inbreeding

Answer 11

The fusion of 2 gametes from close relatives.

Many plant species are natural inbreeders eg. rice, peas.

Breeders try to concentrate alleles for a desirable characteristic into one cultivar (plants) or breed (animals), to create offspring which are superior to their parents.

It works best in natural inbreeders, as harmful recessive alleles are removed by natural selection.

Question 12

Negative effects of inbreeding

Answer 12

Loss of heterozygosity, which allows harmful recessive alleles to be expressed.

Inbreeding depression - a decrease in size, yield, fertility and vigour.

Reduce by choosing individuals which are homozygous for desired characteristics, but heterozygous and diverse for others.

Question 13

Crossbreeding

Answer 13

Introduces new alleles into a crop or animal line, to reduce inbreeding depression in natural outbreeders.

A particular strain is crossed with a different strain with new, desirable alleles.

Question 14

Backcrossing

Answer 14

Cross with the original parent strain, and use selective breeding to remove unwanted alleles.

Question 15

F1 hybrids

Answer 15

Individuals resulting from a cross between 2 genetically dissimilar pure breeding parents of the same species.

Question 16

Hybrid vigour

Answer 16

F1 hybrids are all heterozygous for the desired characteristic

Often have improved yield, vigour or fertility, as poorer recessive alleles are masked by superior dominant ones.

Question 17

F2 generation

Answer 17

Results from breeding 2 members of the F1 generation together.

Contains a variety of genotypes, with many offspring lacking the superior characteristics of the F1 generation.

Question 18

Use of genetic technology

Answer 18

Use genome sequencing to identify organisms carrying particular alleles.

Use these organisms in breeding programmes to introduce specific alleles into a line.

Or isolate the allele and introduce into a host species using recombinant DNA technology.

Use the transformed organism for breeding.

eg. golden rice (to treat vitamin a deficiency); maize containing Bt toxin (insecticide protein).