Hereditary and Environmental Influences on Childbearing

Hereditary and environmental factors influence a person’s development, even before conception. Hereditary factors refer to the genetic determination of traits, like eye color or the inheritance of disorders, like cystic fibrosis. On the other hand, environmental factors refer to external influences found where people live, work, and play that can impact how genes are expressed. Often, the impact on a person’s development is multifactorial, meaning it results from a combination of hereditary and environmental factors.

The hereditary material that determines a person’s development is contained in their chromosomes. Tightly packed into each chromosome is DNA, which is organized into genes that carry a person’s unique genetic code.

During fertilization, each parent donates half their chromosomes to create a fertilized ovum, called a zygote, which contains a total of 46 chromosomes organized into 23 pairs. These chromosome pairs are numbered from 1 to 22, with the 23rd pair, the sex chromosomes, labeled as X or Y.

Now, if chromosomes are altered, the person’s development can be negatively affected. These chromosomal alterations can involve changes in the structure of a chromosome, and can involve deletions, duplications, translocations, and inversions.  

A deletion is when part of the DNA is missing, like with cri-du-chat syndrome, where the short arm of chromosome 5 is missing.  

If there’s extra genetic material in a chromosome, it’s called duplication, like when there’s an extra copy of some of the genes found in the long arm of chromosome 7, resulting in developmental delay, behavioral problems, and other anomalies.  

Another structural alteration is translocation, where part of a chromosome moves to another chromosome. An example is the Philadelphia chromosome, which is chromosome 22 with a bit of chromosome 9 on it, resulting in a type of leukemia.  

Lastly, an inversion, which is where part of a chromosome is rearranged in reverse order. Inversions often result in spontaneous abortions or infertility.

There are also chromosomal alterations that involve changes in the number of chromosomes. Monosomy can happen if one of the chromosomes in a pair is missing, trisomy is when an extra chromosome is added to a pair.  

An example is trisomy 21, where there are three copies of the 21st chromosome, resulting in Down syndrome.  

A trisomy can happen with sex chromosomes, too. So, in Klinefelter syndrome, there’s an extra X chromosome, or XXY, where the affected person is genetically male, but hypogonadism, or underdeveloped genitals, testosterone deficiency, and infertility are also present.