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Lecture 5

BIOLOGY 1A03 Lecture Notes - Lecture 5: Meiosis, Chromosome

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Rosa Da Silva

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Theme 5 Module 3 Part B
Recombination of Alleles
- During recombination of alleles, the position of genes does not change, but the relative
association of alleles does. If the linked genes are far enough apart, recombinant chromatids
that carry alternate allele combinations are generated during crossover events.
- However, if the linked genes are immediately adjacent to each other with very little distance
in between, there would be no crossing over during meiosis I or any crossovers that did occur
would not be in the region between these two genes.
- Since the recombination between linked genes is dependent on the distance between them,
genes that are closer together show less recombination frequency than genes that are located
far apart from each other.
Unit 3: Constructing Linkage Maps
Linkage Map
- Genes that are in close proximity to each other on the same chromosome are inherited
- Examining this pedigree on the inheritance and segregation of the colour-blindness and
haemophilia traits through a family shows us that these two traits are linked.
- But note the exception in the individual with only hemophilia in generation IV. Linkage between
the gene for haemophilia and colour-blindness would lead to the prediction that these two
genes should be inherited together, espeially sie that ale’s other was a arrier for oth.
The fact that they are not in these individuals is explained by the fact that the separation of
these alleles must have occurred by crossing over or recombination of alleles.
- The frequency of these types of exceptions can certainly tell us something about the distance
between genes. The relative distance between genes on a chromosome then allows
researchers to create a linkage map. A linkage map will show not only the distance between
chromosomes, but can also show the order of genes along the chromosome.
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