Unit 3 Sustainability and interdependence Plant and animal

Unit 3 Sustainability and interdependence

Plant and animal breeding

KA 2 a Manipulating heredity Breeders have been manipulating heredity for thousands of years Selective breeding is the process by which selected individuals are bred together to produce offspring with desirable features e. g. improved cultivars of plants and or breeds of animals. These improvements help us to ensure sustainable food production

Manipulating heredity Farmers and breeders select plants and animals with the required characteristics to be parents of the next generation. This brings together desired alleles so that the offspring are more useful than the parents. Many desirable characteristics have been bred into plant crops and animal breeds.

Desirable characteristic Example Higher yield Increase in mass of food produced by wheat Higher milk yield Dairy cattle Higher beef yield Beef cattle Higher nutritional value Increase in mass of protein produced by soya bean crop Resistance to pests Resistance of tomato to eelworm Resistance to disease Resistance of potato to late blight Resistance to frost Strawberries Possession of useful physical characteristics Growth of cereal crop to uniform height suited for mechanical harvesting Ability to thrive in Ability of maize to grow in cold, damp climate. particular environment

How did we get from this …. .

. . to this?

Grey wolf

Ancestral cattle Selectively bred for milk Selectively bred for beef

Selection in plants: cabbage family

Sustainability and Interdependence KEY AREA 2 a – Plant and Animal Breeding 1. Testing Your Knowledge 1 Page 252 2. What you should know page 263 Q 1 (1 -2 for pupils with no N 5) 3. Problem Solving page 65 Q 1 -3 Q 1 -2

KA 2 b Plant field trials A plant field trial is a type of investigation, set up to: • compare the performance of two different plant cultivars (e. g. conventional versus GM) under the same set of experimental conditions; • find out the effect of different environmental conditions on a new cultivar of crop plant.

Designing a plant field trial Selection of treatments For each equal sized crop only one variable should be altered e. g. concentration of fertiliser. All other variables should remain constant to ensure that a fair comparison can be made.

Designing a plant field trial Once the factor to be investigated has been decided, the following factors must be considered: • • • selection of treatments to be used; number of replicates to be included; randomisation of treatments. Example: conducting a field trial to investigate the effect of the concentration of nitrogenous fertiliser on a new cultivar of cereal plant.

Designing a plant field trial Number of replicates To minimise experimental error then a minimum of three replicates must be set up. The more replicates are set up the more reliable the results. This takes account of and minimizes variability within the sample. [Experimental error: differences in each plot and in how the experiment was carried out. ]

Designing a plant field trial Randomisation of treatments In this field 4 treatments (a, b, c and Block d) are being a b investigated, each repeated 3 times. Designing a. Aplant field trial If the plots in a field are treated in an orderly way then bias may exist e. g. one side of the field may be wetter. B C c d a b c d Non-randomised field trial

Designing a plant field trial Randomisation of treatments Randomisation helps eliminate bias. Block a d b c b a c d d b a c A B C Randomised field trial

Metabolism and Survival Questions KEY AREA 2 b – Plant Field Trials 1. Testing Your Knowledge 1 Page 252 Q 4 2. What you should know page 263 Q 4 -5 3. Problem Solving page 65 Q 4

Variation (Revision of National 5 slides 19 -29) The differences that occur both between different species and within the same species are called variation. Variation can be: • continuous e. g. mass of seeds • discrete e. g. flower colour Variation is caused by two factors: • inherited factors in genes from parents • environmental factors i. e. when features are affected by environment.

Genetic terminology – N 5 recap PHENOTYPE • appearance of an organism GENOTYPE • its genetic constitution ALLELES • different forms of the same gene [characteristic showing discrete variation is often controlled by the alleles of a single gene] HOMOZYGOUS • having two identical alleles

Genetic terminology – N 5 recap HETEROZYGOUS • having two different alleles of a gene DOMINANT ALLELE • allele that is always expressed RECESSIVE ALLELE • allele that is only expressed when homozygous TRUE-BREEDING • organism that always produces the same phenotype when crossed with itself

Genetic terminology – N 5 recap Characteristic Dominant trait Recessive trait Plant height Tall Short Pod shape Inflated Constricted Seed colour Green Yellow Seed shape Round Wrinkled Flower colour Purple White

White Mouse (bb) Black Mouse (BB) X X Black Mouse (BB) White Mouse (bb) True breeding

MONOHYBRID (SINGLE GENE) CROSS: • a cross involving only one difference in an inherited characteristic e. g. coat colour in mice:

Monohybrid cross Black Mouse (BB) White Mouse (bb) X Black Mouse (Bb) X Black Mouse (BB) Black Mouse (Bb) 3 Black Mice Black Mouse (Bb) White Mouse (bb) : 1 white mouse

Monohybrid cross e. g. flower colour in peas: R – red; r - white Generation P (Parent) Red x White RR rr gametes all R all r F 1(first Filial) gametes all Red x F 1 Rr Rr R and r F 2 3 Red: 1 White 1 RR : 2 Rr : 1 rr

Test cross What genotype could this brown mouse have? How can you tell if this brown mouse is BB or Bb? A test cross is a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait.

Brown mouse (? ) White mouse (bb) Brown mouse (? ) X X ½ brown mice All brown mice b White mouse (bb) ½ white mice b b b B Bb B b B b b b The genotype of the unknown mouse must have been BB mouse must have been Bb

Polygenic inheritance A characteristic showing continuous variation (e. g. height) is controlled by the alleles of more than one gene – it shows polygenic inheritance. The effect of the genes involved is additive. The greater the number of genes involved, the greater the number of intermediate phenotypes produced. Many traits showing polygenic inheritance are influenced by the environment.

Metabolism and Survival Questions KEY AREA 2 c – Inbreeding 1. Testing Your Knowledge 2 Page 256 Q 1, 2(b-e) 2. What you should know page 244 Q 6 -11 3. Problem Solving page 65 Q 8

Outbreeding (Information only) Outbreeding involves the fusion of two gametes from unrelated members of the same species. Wild animals and cross-pollinating plants are naturally outbreeding e. g. crop plants such as tomatoes, sugar beet and maize. Outbreeding promotes heterozygosity.

KA 2 c Inbreeding • involves the fusion of two gametes from close relatives; • promotes homozygosity; • is naturally occurring in some species of selfpollinating plants e. g. peas, wheat and rice; • ensures that each generation receives the alleles for the desired characteristics. [Recessive alleles are eliminated by natural selection. ]

Effects of inbreeding Desired effect Selected plants or animals are bred for several generations until the population breeds true to the desired type. Negative effects 1. Loss of heterozygosity (not a problem for naturally inbreeding plants) 2. Inbreeding depression

Loss of heterozygosity Heterozgosity Aa (selfed) P F 1 AA F 2 AA AA F 3 Aa AA Aa Aa aa 100% Aa aa AA Aa Aa aa aa aa 50% 25% 4 AA 4 AA 4 AA AA AA 4 aa 4 aa 4 aa 12. 5% 2 Aa 2 Aa aa aa

Inbreeding depression If a natural outbreeder is forcibly inbred, problems arise due to homozygous recessive alleles that may be harmful (usually masked). This is called inbreeding depression.

Inbreeding depression This often leads to a decline in vigour, size and fertility e. g. in maize – the plant on the left is the original parent that was forcibly inbred. Avoidance of depression Parent plants selected are homozygous for desired characteristics but heterozygous for others. Inbreeding depression in maize

Effects of inbreeding in humans The Vadoma tribe of Zimbabwe have Ectrodactyly (two toed feet). This mutation is more common due to inbreeding.

KA 2 d Crossbreeding and F 1 hybrids Inbreeding is not usually carried out indefinitely because of the problems associated with it. New alleles can be introduced into a plant or animal species by crossbreeding with a strain with a different but desired genotype. In animals, individuals from different breeds may produce a new crossbreed population with improved characteristics.

F 1 hybrids F 1 hybrid: an individual resulting from a cross between two genetically dissimilar parents. Breeders cross members of one variety of a species having a desired characteristic with members of another variety that have another desired characteristic in an attempt to produce a hybrid that has both desirable characteristics.

The two parent breeds can be maintained to produce more crossbreed animals showing the improved characteristic

F 1 hybrids In plants a cross between two different homozygous parents creates a uniform F 1 generation. In inbreeding animals and plants, F 1 hybrids are not usually bred together as the F 2 produced shows too much variation. F 1 hybrids have to always be produced from true-breeding parents therefore the parent breeds have to be maintained.

Hybrid vigour In plants F 1 hybrids have increased: • vigour • yield and • fertility because recessive alleles are masked by superior dominant alleles. • disease resistance Parent 1 F 1 hybrid Parent 2

KA 1 e Genetic technology Plants and animals can also be enhanced by use of genetic technologies such as genome sequencing and genetic transformation. • Genome sequencing can be used to identify organisms that possess alleles for a desired characteristic. These organisms can then be used in breeding programmes. • Genetic transformation. Single genes for desirable characteristics can be inserted into the genome of crop plants

Genetic technology Genetic transformation can be used to enhance a crop species which can then be used in a breeding programme. Gene(s) added Host Benefit Examples organism Gene for Bt toxin (kills insects), taken from soil bacterium Crop plants Crop resistant to insect pests; more e. g. maize photosynthesis resulting in higher yield. Genes for vitamin A Rice ‘Golden’ rice that provides vitamin A; better nutrition. Gene for herbicide resistance (from naturally resistant plants) e. g. glyphosate resistant gene Soya, maize, sorghum Herbicide kills weeds without damaging crop; Less competition for light, water and nutrients so increased photosynthesis and yield increased.

Metabolism and Survival Questions KEY AREA 2 c – Genetic Technology 1. Testing Your Knowledge 3 Page 256 Q 1 -3 2. What you should know page 263 Q 12 2. Problem Solving page 65 Q 9

Removed material on next slide (in case they put it back in next year!!!!)

Back crossing Back cross: crossing of an F 1 hybrid with one of its parents or with a genetically identical individual. Back crossing may be used to incorporate a required gene from a parent while maintaining other desired features e. g. cultivated tomatoes are crossed with eelworm-resistant wild tomatoes; the F 1 are back crossed with the cultivated parent for several generations until most wild genetic material (apart from resistance to eelworm) has been eliminated.