Key Area 3: Crop protection Unit 3: Sustainability and Interdependence

Breeding Characteristics of plants and animals can be selected and manipulated by breeders. This is done in order to produce new and improved animal breeds or plant cultivars. Cultivar: a plant variety produced in cultivation by selective breeding. CfE Higher Biology Sustainability and Interdependence

Breeding Characteristics Plant crop or Animal BreedDesirable Characteristic that increases food production WheatHigh grain yield PotatoResistance to fungal disease Soya beanHigh protein content of seeds StrawberryResistance to frost Dairy cattleHigh milk yield Beef cattleHigh meat yield CfE Higher Biology Sustainability and Interdependence

Variation CfE Higher Biology Sustainability and Interdependence There are two types of variation: – Continuous – Discontinuous or discrete Continuous variation is variation that has no limit on the value that occur within a population e.g. height, weight, finger length, leaf length. Distribution curve. Bell shaped normal distribution

Variation CfE Higher Biology Sustainability and Interdependence Discontinuous variation is variation that has distinct groups for organisms to belong to e.g. tongue rolling, blood groups, eye colour.

Discrete variation Inherited characteristics can show discrete variation. This can be used to separate members of a species into 2 distinct groups. – e.g. peas can be separated into colour: green and yellow. CfE Higher Biology Sustainability and Interdependence

Gene Inheritance What do the following words mean when looking at gene inheritance: – Dominant, recessive, true-breeding, heterozygous, homozygous, genotype, phenotype, F1 generation, F2 generation, monohybrid cross, test cross? CfE Higher Biology Sustainability and Interdependence

Gene Inheritance Dominant: the gene that is expressed, usually given a capital letter e.g. A. Recessive: the gene that will not expressed if alongside a dominant gene, usually given a lowercase letter e.g. a. True-breeding: contains 2 alleles for a particular gene that are the same e.g. aa or AA. Heterozygous: contains 2 different alleles for the same gene e.g. Aa. Homozygous: contains 2 identical alleles for the same gene e.g. aa or AA. CfE Higher Biology Sustainability and Interdependence

Gene Inheritance Genotype: the alleles that are expressed Phenotype: the physical characteristics that are expressed. F1 generation: first filial generation, the first generation formed from a cross between two parents. F2 generation: offspring of a F1 generation. Monohybrid cross: a genetic cross that involves only one difference (one gene) in an inherited characteristic. Test cross: genetic cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait. Back cross: cross between F1 hybrid with a parental type to maintain characteristics of a new breed. CfE Higher Biology Sustainability and Interdependence

Gene Inheritance Carry out crosses to the F2 generation for the following : (round is dominant, wrinkled is recessive) 2 parent plants that are true breeding for round seeds. 2 parent plants that are true breeding for wrinkled seeds. 1 parent plant that is true breeding for round seeds and 1 parent plant that is true breeding for wrinkled seeds. CfE Higher Biology Sustainability and Interdependence

Test Cross In cattle the presence/absence of horns is controlled by a single gene with two alleles. Polled or hornless (P) is dominant to horned cattle (p). Carry out a cross between these two homozygous cattle to the F2 generation. Once the F2 generation is gained there is no way to tell what their genotype is by looking at them. They could be either Pp or PP. In order to find out the genotype of these animals a test cross can be carried out. CfE Higher Biology Sustainability and Interdependence

Test Cross Is the bull PP or Pp? Test cross 1: ?X pp Test cross 2:?Xpp CfE Higher Biology Sustainability and Interdependence GametesPP PPp P If all offspring have no horns then the unknown genotype must be PP GametesPp pPppp pPppp If half the offspring have no horns and half horns then the unknown genotype must be Pp

Polygenic inheritance Characteristics that are important to breeders e.g. birth weigh and weaning weight in cattle; marbling (fat streaks in lean meat), seed length and shape show polygenic inheritance. In humans, skin colour and height are examples of polygenic inheritance. Polygenic inheritance means that the characteristic is controlled by more than one gene. The more genes that are involved then the greater the number of intermediate phenotypes can be produced. CfE Higher Biology Sustainability and Interdependence

Selecting and Breeding Over the centuries, farmers and increasingly scientists have been involved in manipulating the characteristics of plants and animals in order to obtain higher yields and thus ensure sustainable food sources. CfE Higher Biology Sustainability and Interdependence

Plant field trials Plant field trials are used to – compare the performance of different cultivars or GM crops. – find out the effect of different environmental conditions on a new cultivar. Explain how each of the following are involved in the design of a trial. 1.Selection of treatments 2.Number of replicates 3.Randomisation of treatments CfE Higher Biology Sustainability and Interdependence

Plant field trials 1.Selection of treatments: The number of treatments and if they are valid to compare e.g. using wildtypes or other cultivars to compare. 2.Number of replicates: Several replicate required to ensure reliability of results. Reduces effect of experimental error and variability. Allows statistical analysis of results. CfE Higher Biology Sustainability and Interdependence

Plant field trials 3. Randomisation of treatments: The ordering of the plots within the trial should be random to remove observer bias. CfE Higher Biology Sustainability and Interdependence

Selecting and Breeding Plants or animals with the desired characteristics are identified. These are then used as the parents of the next generation. The aim is to combine the alleles of a gene for a desired trait present in one parent with the alleles of a gene for another desired trait in the second parent. Thus creating offspring which have superior characteristics to their parents. CfE Higher Biology Sustainability and Interdependence

Outbreeding Outbreeding occurs when individuals breed across the whole gene pool. No selection is involved. Outbreeding occurs in normal cross pollinating plants and animals. Some plants possess mechanisms to prevent self-pollination. CfE Higher Biology Sustainability and Interdependence

Inbreeding Inbreeding occurs when individuals breed within a particular gene pool, usually with close relatives. Self-pollinating plants are the most extreme case of inbreeding. Inbreeding can be used over several generations in order to eliminate certain heterozygous traits. CfE Higher Biology Sustainability and Interdependence

Inbreeding Depression If inbreeding continues over a long period of time, heterozygosity can decrease and homozygosity can develop. In self pollinating plants this is not a problem as harmful or deleterious alleles are removed by natural selection. However, if inbreeding is forced inbreeding depression can happen. This means that recessive homozygous alleles can appear. CfE Higher Biology Sustainability and Interdependence

Inbreeding Depression Inbreeding depression can result in : Reduced vigour, size, fertility and yield CfE Higher Biology Sustainability and Interdependence

Cross breeding Cross breeding is carried out to prevent this accumulation of harmful alleles. This involves the introduction of new alleles into a population. This is carried out by breeding a plant or animal with a strain containing a different but beneficial genotype. CfE Higher Biology Sustainability and Interdependence

Cross breeding Once a new breed has been produced with advantageous alleles, it must be maintained. There are two main ways to maintain the ‘new’ breed. Write an explanation of these two methods and an advantage and a disadvantage. CfE Higher Biology Sustainability and Interdependence

Selective breeding and test crossing in the F2 to check genotype Advantage: – Can produce a group of individuals that can sustain the population. Disadvantage: – Takes time CfE Higher Biology Sustainability and Interdependence

Maintaining the two parent breeds Advantage: – Can produce more of the F1 generation at any time. Disadvantage: – Both parent breeds must be maintained CfE Higher Biology Sustainability and Interdependence

Use of F1 Hybrids An F1 hybrid is formed from a cross between two genetically dissimilar parents of the same species F1 hybrids are often used in plant breeding. What is meant by hybrid vigour? The first generation has characteristics of both parents and often this means they are most ‘vigorous’ and have a higher yield. Why is the F2 generation not as useful as the F1? The F1 will be a uniform group of heterozygotes, breeding to the F2 will produce a wide genetic variation, so production will be less controlled. CfE Higher Biology Sustainability and Interdependence

Genetic Technology Increasingly genetic technologies are being used in breeding programmes. Explain how the following technologies have been (or could be) used in breeding. 1. Genetic transformation 2. Genome sequencing 3. Gene probes CfE Higher Biology Sustainability and Interdependence

Genetic Technology 1.Genetic transformation Using genes from other species and introducing these to the genome of the plants that are being worked with e.g. introducing the Bt gene for pest resistance. 2. Genome sequencing allows identification of genes that have desired characteristic and the individuals that are carrying these alleles. CfE Higher Biology Sustainability and Interdependence

Genetic Technology 3. Gene probes use of these identifies whether the gene is homozygous/heterozygous or there is a presence/absence of particular markers which will decide on breeding. CfE Higher Biology Sustainability and Interdependence