Question

explain the concept of linkage. if you performed a test cross with a fruit fly that is heterozygous for two genes how could you conclude that the two genes are linked

Answer 1

Linkage involves genes that are close together on the same chromosome, often leading to inheritance patterns where the parental allele combinations are transmitted together. A test cross can reveal linkage when there are fewer recombinant genotypes than expected. Geneticists can use linkage information to create maps that illustrate gene locations on chromosomes.

Step-by-step explanation:

The concept of linkage refers to genes that are located in close proximity on the same chromosome and therefore tend to be transmitted through meiosis together. To determine if two genes are linked, one may perform a test cross with a heterozygous fruit fly for two genes. If most offspring display parental genotypes, and there are fewer recombinant genotypes (indicating allele combinations not found in the parents), this suggests linkage.

This is because the close proximity of the linked genes on the chromosome reduces the likelihood of crossing-over between them during meiosis. A significant ratio of non-parental genotypes in the offspring would indicate that crossing-over has occurred, suggesting either that the genes are not linked or that they are linked but far enough apart on the chromosome to allow crossing-over.

Using genetic analyses such as a Punnett square or calculating recombination frequencies, scientists can infer the likelihood of genes being linked. Observations that confirm linkage typically show a significant deviation from the expected 9:3:3:1 ratio in the offspring, which would be seen if the genes were segregating independently. Ultimately, if two genes are found to be linked, geneticists can utilize this information to construct linkage maps that show the locations of genes on chromosomes.

Answer 2

The correct answer would be - the ratio of phenotypes in an organism cross will tell if the genes are linked or not.

Step-by-step explanation:

In this question, we perform a test cross with a fruit fly that is heterozygous If we perform a test cross between two parents with identical heterozygous genomes AaBb.

If there is no recombination found in the offspring of this cross it means there are no linkage of genes present. And if there are new or recombinant phenotypes present it means that there are genes linked together.