BIO120 Meiosis and Mitosis-OPEN University

Open University

S103_5
8 Hours

Level

Introductory

Course Home (Click Here)

Course Description

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. Then you will examine how genes are transmitted in particular patterns from generation to generation. These two approaches combine to illustrate how the patterns of inheritance can be explained by the behaviour of chromosomes during sexual reproduction.

Learning Outcomes

After studying this Unit you should know:

the number of chromosomes is characteristic of each species and can vary enormously between species

genetics is based on the concept of the gene as the unit of inheritance

that sexual reproduction always includes two distinctive processes: the production of gametes, which involves meiosis, and fertilisation. The two processes are accompanied by changes in the chromosome number, from diploid to haploid and from haploid to diploid, respectively

a particular phenotypic character is determined by the two copies of a gene that an organism possesses and these two copies are identical in a pure-breeding variety

when organisms with contrasting characters for which they are pure-breeding are crossed, the dominant character appears in the first offspring or first filial generation and the recessive character is masked

the genotypic ratios of a cross result from the separation of the two copies of a gene to different gametes in equal numbers, and because gametes combine at random at fertilisation. The expected ratios in genetics do not tell us the actual ratios observed, but rather the most probable ratios

the behaviour of chromosomes at meiosis explains the segregation of the two copies of a gene and the independent assortment of genes. The linkage of genes on a chromosome can be broken by means of crossing over

recombination – the production of new combinations of alleles – arises during meiosis from independent assortment of chromosomes and crossing over between homologous chromosomes

the amount of crossing over between linked genes differs according to their distance apart.

	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

Citation: administrator. (2010, January 29). BIO120 Meiosis and Mitosis-OPEN University. Retrieved July 31, 2010, from Free University Courses OCW Courses OpenCourseWare Freeversity Foundation Web site: http://www.freeversity.org/science-and-mathematics/biology/bio120-meiosis-and-mitosis-open-university.

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