A gene is a basic unit of heredity and is made up of a sequence of nucleotides in DNA or RNA. Genes carry information that determine traits, and are passed on from parents to their offspring. Every individual contains approximately 20,000 to 25,000 genes, including two copies of each gene, one from each parent.
A gene is a basic, functional unit of inheritance passed from parents to children. Genes are segments of DNA that code for a specific genetic trait, such as eye color, height, or inherited disease; many of them are responsible for making proteins. They are organized linearly on structures called chromosomes. It is estimated that humans have 20,000 to 25,000 genes within 46 chromosomes (23 pairs).
The term “genetic” means relating to genes and DNA. A genetic mutation is a change in the DNA sequence of a gene, and contributes to aspects of human diversity as well as disease.
Research indicates that genetic factors contribute to 15–30% of male-factor infertility cases. The genetic factors that may be involved in male infertility include balanced translocation; gene mutations; inherited disease like cystic fibrosis, Kallman syndrome, or Klinefelter syndrome; and Y-chromosome deletions. Genetics can also contribute to multifactorial disorders like diabetes and heart disease, and endocrine disorders like hormone dysfunction and thyroid dysfunction, which may also impact male fertility. Genetic disorders or abnormalities can lead to impaired spermatogenesis, low or no sperm count, and/or low sperm quality.
There are a variety of tests that can determine if there are changes in chromosomes or genes, such as karyotype analysis, which screens for azoospermia factor (AZF) microdeletions. Some with chromosome abnormalities, microdeletions, or single-gene mutations can still conceive a child using in vitro fertilization (IVF) with intracytoplasmic injection (ICSI).
Gregor Mendel's memoir on plant hybridization in 1865 is considered the origin of genetics, although the word “genetics” was not coined until 1906. This new science of heredity introduced biological concepts of genes, genotypes, and phenotypes, based upon the Mendelian method for analyzing patterns of inheritance that are characteristic of reproductive organisms.
In the 1910s, Mendelian genetics merged with the chromosomal theory of inheritance to create classical genetics, in which the gene was considered a unit of function, transmission, recombination, and mutation. In the 1950s, the discovery of DNA advanced the conversation, as scientists found that the double-helical model contained the code by which genetic information could be stored and transmitted.