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Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis Blueprint of Life Topic 20: Hybridisation.

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Presentation on theme: "Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis Blueprint of Life Topic 20: Hybridisation."— Presentation transcript:

1 Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis Blueprint of Life Topic 20: Hybridisation

2 DOT POINT(s) process information from secondary sources to describe an example of hybridisation within a species and explain the purpose of this hybridisation.

3 Introduction The term reproductive technology applies to any use of technology to assist and improve reproduction. Current reproductive technologies and genetic engineering are the culmination, over many hundreds of years, of the efforts of humans to improve the quality and yield of their food.

4 Introduction At first, humans obtained food by hunting and gathering; they then began raising their own animals and growing their own crops and soon realised the advantage of selecting seeds from the best crops and breeding the best quality animals, to improve the quality and yield of future generations.

5 Introduction This was the start of selective breeding or artificial selection, involving the human ‘manipulation’ of living organisms by selecting those which should breed, ensuring they pass on their favourable characteristics.

6 Introduction The trend to ‘manipulate’ the phenotype of offspring to achieve desirable characteristics has continued over many hundreds of years, becoming more sophisticated as technology has improved. The older techniques of artificial pollination (plants) and selective breeding are still used, together with modern-day reproductive technologies which include artificial insemination (animals), in vitro fertilisation, embryo transfer and cloning, amongst others.

7 Introduction This advanced technology allows more specific selection and breeding, and has led to the even more advanced technology of inserting desired genes into organisms by genetic engineering. Genetic engineering is only considered a reproductive technology if the gene being inserted has the effect of assisting reproduction (e.g. increasing fertility).

8 Introduction The manipulation made by humans using reproductive technologies is a contentious issue, raising ethical considerations—an area of study known as bioethics has developed to help people make wise decisions when important values are at stake.

9 Introduction The advanced technologies such as cloning and genetic engineering make it much easier for humans to tamper with the human genome and recombine genes of different species. This raises issues of human rights and animal rights and also how ‘tampering with nature’ may alter the path of evolution as a result of using these technologies.

10 Hybridisation The term hybridisation means the crossbreeding of two genetically non-identical individuals. This may mean crossing parents of the same species, who show genetic variation (intraspecific hybridisation), or it may extend to parents of different species (interspecific hybridisation).

11 Hybridisation We are now going to look at examples of hybridisation within a species (intraspecific). Within the units classified as species, there are populations that may be more or less distinct from each other. These groups are called ‘races’ or, more scientifically, subspecies or varieties. When discussing hybridisation students are expected to describe intraspecific hybridisation of varieties or subspecies, not hybridisation between species.

12 The Purpose of Hybridisation Hybridisation involves cross-breeding as opposed to in-breeding. It occurs both in nature and artificially (e.g. as a result of human manipulation of breeding—known as selective breeding). Cross- breeding or hybridisation is commonly used in horticulture and agriculture to improve the quality of the plants and animals being grown or raised.

13 The Purpose of Hybridisation Selective breeding occurs at two stages in the hybridisation process: ■ selecting parent individuals with desirable traits and then breeding them in the hope that some offspring will inherit a combination of these desirable traits ■ selecting offspring that reflect the desired combination of traits for further breeding.

14 The Purpose of Hybridisation The result is the production of hybrid offspring with combined traits that make them better suited to their environment or to meet their end use (e.g. bigger flowers, higher nutrient value, increased crop yields, more suitable breeding time, greater resistance to drought or disease or salinity and higher stamina).

15 The Purpose of Hybridisation Successful hybridisation leads to hybrid vigour —increased strength, better health and greater fertility in the hybrid individuals than is usually found in the homozygous individuals from which they were bred. Hybrids often display advantages that are not present in either of the parental varieties, as a result of the compounded effects of their new gene combinations, giving new phenotypes on which natural selection can act.

16 The Purpose of Hybridisation Advantages of hybridisation ■ It increases genetic variety. ■ It may combine the best feature of each parent, resulting in hybrid vigour.

17 The Purpose of Hybridisation Disadvantages of hybridisation ■ It may combine the weaker features of each parent and the offspring would have less stamina, less resistance to disease or changes in the environment, lower crop yields, and so on. ■ It is a costly procedure, especially if the resulting offspring do not display hybrid vigour. ■ Sometimes the hybrid offspring are infertile or have reduced fertility (they may be heterozygous for some genes where the homozygous condition gave a breeding advantage to the parent generation).

18 The Purpose of Hybridisation ■ Hybridisation is often followed by selective interbreeding of the resulting hybrids with each other to maintain the favourable combination of traits within the population. This equates to in- breeding the hybrids and negative effects may become apparent in other traits; e.g. in chickens that have been cross-bred to create a high clutch yield (increased egg laying), subsequent in-breeding of these hybrids has resulted in eggs with very thin shells that break easily.

19 An Example of Hybridisation In 1870, William Farrer (a 25- year-old mathematics graduate and medical student) moved to Australia from England. He was employed by the Department of Lands in the Dubbo to Cooma districts and later began farming.

20 An Example of Hybridisation Farrer was aware that wheat growing in Australia was presenting problems—the strains being grown (in particular the English varieties) were not suited to the harsh, dry environment, were susceptible to disease such as rust, matured early and the grain quality was not of a high enough standard for milling and baking.

21 An Example of Hybridisation Farrer’s selected two different varieties of wheat, each containing a desired trait for growing in Australia’s harsh conditions. ■ Indian wheat was drought- tolerant and resistant to some diseases. ■ Canadian Fife wheat matured late and had the best milling and baking qualities.

22 An Example of Hybridisation Farrer hybridised these two varieties and then selected plants that had the advantages of both parents, to produce many hybrids, of which one was the Bob’s variety, the first commercially grown wheat variety in Australia. He also created a Fife–Indian wheat variety called Yandilla from these parent varieties.

23 An Example of Hybridisation Another extremely successful hybrid was the result of his cross between a Purple Straw variety, 14A, and his a Fife–Indian wheat variety Yandilla. This resulting variety called Federation (named in 1901) had the hardiness of the Indian variety, a tendency to escape rust disease and short, strong straw that made it ideally suited to the Australian climate and harvesting methods.

24 An Example of Hybridisation Farrer’s wheat hybridisation success was evident when, by the year 1914, 22 varieties out of the 29 grown in New South Wales were Farrer wheats. Farrer’s studies also contributed to an understanding that factors such as diseaseresistance, grain quality and maturing time in wheat can be inherited.

25 An Example of Hybridisation Today, hybridisation and selective breeding still play a role in agriculture in Australia, along with advanced biotechnological techniques such as cloning and genetic engineering to create transgenic species.

26 The DOT Point The word species in Latin means ‘kind’, as used in ‘different kinds’ of organisms. A species is a group of organisms that can interbreed and give rise to fertile offspring (that is, offspring that are able to reproduce).

27 The DOT Point Therefore to address hybridisation within a species (intraspecific hybridisation as opposed to interspecific hybridisation), the selection of examples should not include creatures such as mules or any other hybrids across species.

28 The DOT Point Examples that meet the criteria of this dot point are: ■ corn hybridisation ■ grape hybridisation ■ cattle breeding (e.g. Hereford Angus) ■ seedless watermelons ■ dog hybridisations (e.g. labradoodles).

29 The DOT Point Examples that do not meet the criteria (that is, examples of hybridisation between species) are: ■ donkey X horse = mule/hinny ■ tiger X lion = liger/tigon ■ cabbage X radish = rabbage ■ emmer wheat X goat grass = common wheat.

30 Activity/Homework -Students to answer the following questions in their notebooks. 1. What is meant by hybridisation? 2. Describe an example of hybridisation within a species and explain the purpose of this hybridisation. a

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