All tasks in genetics, as a rule, come down to several main types: settlement, on clarification of a genotype and on clarification of how the sign is inherited. Similar tasks can be schematic or illustrated. However, for the successful solution of any task including genetic, it is necessary to read its condition attentively. The decision is based on performance of a number of certain actions.
It is required to you
- - notebook;
- - textbook on genetics;
- - handle.
Instruction
1. At first it is necessary to define type of the offered task. For this purpose it is necessary to find out what number of gene couples are responsible for development of the offered signs what signs are considered. To learn gomo- or heterozygotic organisms in this case are crossed among themselves and also whether inheritance of a certain sign is connected with sexual chromosomes.
2. To find out what of the signs offered to study is recessive (weak) and what – prepotent (strong). At the same time at the solution of a genetic task it is necessary to make a start from a prerequisite that the prepotent sign in descendants will be always shown fenotipichesk.
3. To define number and type of gametes. At the same time it should be taken into account that gametes can be only gaploidna. Respectively, distribution of chromosomes during their division happens evenly: each of gametes will contain only on one chromosome taken from homologous couple. As a result the posterity receives on a "half" set of chromosomes from each of the parents.
4. To make schematic record of a condition of a genetic task in a notebook. At the same time prepotent signs for the homozygous studied organism are designated in the form of AA combination, for heterozygotic - Aa. The uncertain genotype has designation A_. The recessive sign registers in the form of a combination aa.
5. To write down phenotypes and genotypes of the individuals crossed on a statement of the problem. Then, being guided by Paragraph 3 (definition of types of gametes), to write down phenotypes and genotypes of the posterity received as a result of crossing.
6. To analyze the received results and to write down this numerical ratio. It will also be the answer to a genetic task.