- Current section: Introduction
- Learning outcomes
- 1 Unit introduction
- 1.1 Meiosis and the life cycle
- 1.2 Like begets like
- 1.3 Patterns of inheritance
- 5 Why not an exact 3:1 ratio?
- 6 Inheritance of more than one pair of contrasting characters
- 1.6 Summary
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Meiosis and mitosis
This Unit looks at how units if inheritance are transmitted from one generation to the...
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 chromosones of animals and plants during the process of sexual reproduciton. 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.
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.
Meiosis and mitosis
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.
This unit is from our archive and is an adapted extract from Discovering science (S103) which is no longer taught by The Open University. If you want to study formally with us, you may wish to explore other courses we offer in.
This is an extract from an Open University course which is no longer available to new students. If you found this interesting you could explore more free Biology course units or view the range of currently available OU Biology courses.