Marriages between close relatives should be avoided as it causes more

The correct option is Recessive alleles to come together.

To understand why marriages between close relatives (also known as consanguineous marriages) should be avoided, we need to look at the genetics of inherited traits and diseases.

Every individual inherits two copies of each gene, one from each parent. These gene versions are called alleles. Many genetic disorders are autosomal recessive, meaning a person must inherit two copies of the defective recessive allele (one from each parent) to actually manifest the disorder. If they inherit only one copy, they are a carrier and typically show no symptoms.

Close relatives, such as cousins, share a relatively high proportion of their DNA because they have common ancestors. Therefore, if a rare, harmful recessive allele exists in a family lineage, the probability that two close relatives both carry that same recessive allele is significantly higher compared to two unrelated individuals in the general population.

When close relatives marry and reproduce, there is a much greater chance that both parents will pass on the same harmful recessive allele to their offspring. This brings the recessive alleles together (homozygosity), which can lead to the expression of genetic disorders or abnormalities in the child.