# How Does Recombination Frequency Affect Genetic Linkage?

• TytoAlba95
In summary: Yes, if we know the distance between the two genes and the number of crossovers that have occurred between them, we can calculate the recombination frequency. In this case, the distance between the two genes is 70 cM, and there have been 2 crossovers between them. Therefore, the recombination frequency is 0.33.
TytoAlba95

## Homework Statement

In a linkage map, two genes A and B, are 70 cM apart. If individuals heterozygous for both the genes are test crossed number of progeny with parental phenotype will be:

1. equal to the number of progeny with recombinant phenotype
2. more than the number of progeny with recombinant phenotype
3. less than the number of progeny with recombinant phenotype
4. could be more or less than the number of progeny with recombinant phenotype depending on whether the genes are linked in cis or trans, respectively2. Solution

3. Attempt
Since the genes are 70 cM apart on a linkage map. The recombinant frequency is more than 50% (In case of true linkage the recombinant frequency should always be less than 50%, i.e. is less than parental frequency, I don't know the reason why.) So this is a case of independent assortment. So in a test cross, the frequency would be 1:1.

SanjuktaGhosh said:

## Homework Statement

In a linkage map, two genes A and B, are 70 cM apart. If individuals heterozygous for both the genes are test crossed number of progeny with parental phenotype will be:

1. equal to the number of progeny with recombinant phenotype
2. more than the number of progeny with recombinant phenotype
3. less than the number of progeny with recombinant phenotype
4. could be more or less than the number of progeny with recombinant phenotype depending on whether the genes are linked in cis or trans, respectively2. Solution

3. Attempt
Since the genes are 70 cM apart on a linkage map. The recombinant frequency is more than 50% (In case of true linkage the recombinant frequency should always be less than 50%, i.e. is less than parental frequency, I don't know the reason why.) So this is a case of independent assortment. So in a test cross, the frequency would be 1:1.

If two genes are 70cM apart on a linkage map, this suggests that, on average, there will be 0.7 crossover events between the two genes during a single generation. This means that some gametes will show 0 crossover events (no recombination) or 1 crossover event (recombination). However, two crossover events occurring between the two genes is also possible, which would result in the gametes showing no recombination between the parental alleles. In order to account for the fact that an odd number of crossover events results in recombination while an even number of crossover events results in no recombination, one can sum over the probabilities to obtain a simple formula for the recombination frequency:
$$P[\text{recombination}|d \text{ cM}] = \frac{1-e^{(-2d/100)}}{2}$$
https://en.wikipedia.org/wiki/Centimorgan

With this information, can you calculate the recombination frequency between the two parental alleles?

## 1. What does it mean for two genes to be linked?

Two genes are considered linked if they are located close together on the same chromosome. This means that during cell division, they are likely to be inherited together as a unit rather than being separated by crossing over.

## 2. How do scientists determine if two genes are linked?

Scientists can determine if two genes are linked by performing a genetic linkage analysis. This involves studying inheritance patterns in families and examining how often certain traits or genes are inherited together.

## 3. What are the implications of two genes being linked?

The implications of two genes being linked can vary depending on the specific genes and their functions. In some cases, linked genes may play a role in the development of certain diseases or disorders. They may also be inherited together, making it more difficult to create genetic diversity.

## 4. Can linked genes ever be separated?

Yes, linked genes can be separated through a process called crossing over. During this process, segments of chromosomes can be exchanged between homologous chromosomes, resulting in the separation of linked genes.

## 5. Are all genes on the same chromosome linked?

No, not all genes on the same chromosome are necessarily linked. Genes can be located far apart on a chromosome and may not be inherited together as a unit. The level of linkage between genes can vary and is dependent on their physical distance from each other.

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