Bio 3.7 Human Manipulation Of Genetic Transfer Selective Breeding

Student Learning Objectives One/Many Idea: Define selective breeding Describe Inbreeding Describe Hybridisation Describe Polyploidy

Which of these is/are not genetically manipulated? Common Wheat Square Watermelons Tiger-looking dog Liger Killer Bee

Genetic Manipulation Genetic Manipulation Selective Breeding Transgenesis Genetic Manipulation Assisted reproduction Whole organism cloning

Selective Breeding Selective breeding is a method by which humans determine the genetic makeup of organisms by controlling breeding It involves selecting for certain desirable traits by: Allowing individuals that have the desired traits to breed Removing (culling) individuals that do not provide desirable traits from the breeding population Inbreeding which results in individuals homozygous for a trait Retain those properties in future generation

Selective Breeding Selective Breeding Hybridisation Inbreeding Repeat breeding of plants and animals with the same desired traits would result in retaining these beneficial properties Hybridisation Breeding between closely related species

Inbreeding: From Wolf to Woof The first animal to be domesticated was probably the wolf (10,000 to 15,000 years ago) Wolf cubs that demonstrated traits of sociability and obedience may have been allowed to remain with groups of humans helping with hunting, guarding and companionship Overtime, selection for specific traits such as size, speed, behavioural traits..etc lead to a huge variety of breeds for specific tasks

Behaviour with other hens Best Egg Imagine you work for the super-chick egg company, and it has been decided the Kendo and Bibby have been chosen to mate Research suggests the following: Supermarkets want large eggs which are brown with yellow yolks Farmers want passive livestock which are healthy What features do you hope will be shown by the offspring? Kendo male bird Bibby female bird Features Kendo family Bibby family No. eggs per week 6 4 Colour of eggs White Brown Size of eggs Medium Large Colour of yolk Bright yellow Pale lemon Resistance to disease Highly resistant Not resistant Behaviour with other hens Aggressive Not aggressive

Behaviour with other hens Super Eggs Kendo male bird Bibby female bird Features Kendo family Bibby family No. eggs per week 6 4 Colour of eggs White Brown Size of eggs Medium Large Colour of yolk Bright yellow Pale lemon Resistance to disease Highly resistant Not resistant Behaviour with other hens Aggressive Not aggressive You would want the following features: 6 eggs Brown eggs Large eggs Bright yellow yolk Highly resistant Not aggressive However there are not guarantees that the offspring will carry all these traits

Development of Crop Species Most modern crop plants are very different from their wild ancestors Two main process have occurred in the past to speed up the development of many staple foods: Hybridisation Polyploidy

Hybridisation Plants hybridise very easily with closely related species to retain desirable traits from both species. Most of these hybrids are sterile but may become fertile by the process of polyploidy Hybrids are sterile: different number of chromosomes and fail to segregate during meiosis and result in sterile

Polyploidy Polyploidy is the sate of having three or more complete sets of chromosomes It is resulted from the failure of separating chromosome pairs (non-disjunction) This state has the benefits of both creating fertile hybrids and the over-expression of certain traits such as seed number or fruit size N = one set of chromosomes, 2N is the “normal state” in most animals. Plants

Hybrid and Polyploidy Scenario 1 Scenario 2

Wheat Common wheat has developed as a result of several polyploid events after the formation of hybrids between different grass species: Goat Grass Genome: DD 2N 14 X Wild Grass Genome: BB 2N 14 Interbreed to form sterile hybrid X Chromosome doubling (polyploidy) makes hybrid viable Interbreed to form sterile hybrid Emmer Wheat Genome: AABB 4N 28 Domesticated in the Middle East Chromosome doubling (polyploidy) makes hybrid viable Common Wheat Genome: AABBDD 6N 42 Wild Einkorn Genome: AA 2N 14 Einkorn Genome: AA 2N 14

Hybridisation Examples Wheat Modern wheat is hexaploid (6N) and has developed from two hybridisations and two occurrences of polypolids Bananas Common cavendish bananas are triploid (3N) which results from hybridisation thousands of years ago. These banana plants are seedless and sterile Luckily bananas are easily grown from cuttings

Work/Homework Workbook, page 234