Meiosis and mitosis

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	Time: 8 hours Level: Introductory

	Introduction Introduction Resource This Unit looks at how units if inheritance are transmitted from one generation to the next. First you will look at what happens to the chromosomes of animals and plants during the process of sexual reproduction....

	Unit introduction Unit introduction Resource Living organisms use the components of the world around themselves and convert these into their own living material. An acorn grows into an oak tree using only water, oxygen, carbon dioxide, some inorganic...

	1: Meiosis and the life cycle 1.1: Chromosomes and the life cycle Resource The type of nuclear division called meiosis is intimately linked to the life cycle of organisms that reproduce sexually. 1.2: Sexual reproduction Resource Sexual reproduction includes two distinctive processes:

	2: Like begets like 2: Like begets like Resource It is possible to follow a character, such as eye colour or hair colour in humans, that is handed down from generation to generation. Such characters are said to be inherited characters (or heritable characters)...

	3: Patterns of inheritance 3.1: Inheritance of colour in maize Resource We can trace the inheritance of characters in animals and plants by following the phenotype from generation to generation, in breeding experiments. We will describe work with maize (Zea mays), alternatively... 3.2: A breeding experiment: stage one Resource In the first stage of the breeding experiment, shown in Figure 5, plants from the pure-breeding purple-grained variety are crossed with (fertilised by) plants from the pure-breeding white-grained variety.... 3.3: A breeding experiment: stage two Resource We now turn to the second stage of the breeding experiment, but this time we will follow the phenotypes and genotypes simultaneously. The purple (Gg) grains of the F1 generation are planted and when these... 3.4: Predicting the outcome of crosses Resource By knowing the pattern of inheritance of genes as described above, it is possible to make some predictions about the phenotypes and genotypes of each generation in breeding experiments. This section considers...

	4: Why not an exact 3:1 ratio? 4: Why not an exact 3:1 ratio? Resource Before we leave the maize breeding experiments we will look more closely at some actual values obtained for the F2 generation and how closely they fit the expected phenotypic ratio of 3:1. Table 2 gives...

	5: Inheritance of more than one pair of contrasting characters 5: Inheritance of more than one pair of contrasting characters Resource We have considered the inheritance of one pair of contrasting characters that involves the segregation of the two copies of one gene in maize. A single chromosome carries many genes, of the order of 2...

	6: Summary 6: Summary Resource The number of chromosomes is characteristic of each species and can vary enormously between species.

	References and Acknowledgements Acknowledgements Resource