Published by the Students of Johns Hopkins since 1896
December 8, 2022

Study shows sex can weed out genetic diseases

By TONY WU | March 5, 2015

Every hour, thousands of couples around the world engage in amorous acts. The rush of endorphins and the bonding that results from sex create a sense of pleasure, but humans also use sex to procreate and ensure the survival of the species.

Without sexual reproduction, the human race may not have developed into the dominant species that we are today. Recently, scientists have found evidence that sex may not only serve as a method for the continuation of the species but also as a way to weed out genes that may cause diseases.

Procreation in humans depends heavily on the production of sperm and the release of eggs. These sex cells are referred to as gametes, and each contains 23 chromosomes, one half of the 23 pairs of chromosomes in humans. Gametes are produced through meiosis, during which crossing over and random assortment occurs. Crossing over randomly mixes segments of homologous chromosomes, creating different combinations. Random assortment, on the other hand, separates the homologous chromosomes into different gametes. Both of these processes randomly mix and match genetic materials and help introduce genetic diversity into the population.

When conception occurs, the gametes combine into 23 pairs of chromosomes, which are the genetic code for the future child. These genes code for diverse areas such as height, appearance and even susceptibility to certain diseases.

Though most students believe that the recombination of chromosomes from both parents occurs similarly for all chromosomes, researchers have long known that chromosomes from each parent do not mix in the same way. Some fragments of the genome are recombined readily, while the others occur rarely during processes such as crossing over. Furthermore, segments in which recombination occurs rarely will eventually form a new combination, but it takes many generations.

A research team led by Philip Awadalla at the University of Montreal found that these segments often carry genes for mutations that may cause diseases. Because these segments are sifted less than other, more rapidly recombining segments, they often collect disease-inducing mutations. On the other hand, as the gene is passed on through subsequent generations, the mutated segments are eliminated through processes of sexual reproduction.

To analyze the role of recombination in disease-inducting mutates, scientists gathered the genetic data of 1,400 subjects from CARTaGENE, a Canadian genetic data bank. They identified disease-inducing mutations and found that the majority exist in spots that undergo less recombination. The findings extend to most major racial groups, including Africans, Asians and Europeans. Despite exhibiting similar trends, African subjects tend to have a smaller proportions of disease-inducing mutations, while Europeans have the largest.

This discovery may result in more successful screening of genetically predisposed diseases. Instead of searching for genes throughout the whole genome, a process that can take hours to days, it may be more efficient to search in areas where there is less recombination. By optimizing genetic screening, it may make these tests more affordable and thus a tool for doctors to treat patients.

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