Several hypothesized chains of causality exist whereby increased<unk> <unk>  may lead to health effects. There are different types of genome mutations, with distinct mutation mechanisms: *DNA length mutations of repetitive DNA (such as telomeres and microsatellites), caused by cellular copying errors *DNA point mutations, caused by cellular copying errors and also by chemical and physical insults such as radiation *chromosome breaks and rearrangements, which can occur in the resting cell *epigenetic changes, i.e. methylation of the DNA, which can activate or silence certain genes, and is sometimes passed down from parent to child Telomere length Telomeres are repetitive genetic sequences at both ends of each chromosome that protect the structure of the chromosome. As men<unk> , most telomeres shorten, but sperm telomeres increase in length. The offspring of older fathers have longer telomeres in both their sperm and white blood cells. A large study showed a positive<unk> , but no independent<unk>  on telomere length. Because the study used twins, it could not compare siblings who were discordant for<unk> <unk> . It found that telomere length was 70% heritable. DNA point mutations In contrast to oogenesis, the production of sperm cells is a lifelong process. Each year after puberty, spermatogonia (precursors of the spermatozoa) divide meiotically about 23 times. By the<unk>  of 40, the spermatogonia will have undergone about 660 such divisions, compared to 200 at<unk>  20. Copying errors might sometimes happen during the DNA replication preceding these cell divisions, which may lead to new (de novo) mutations in the sperm DNA. The selfish spermatogonial selection hypothesis proposes that the influence of spermatogonial mutations in older men is further enhanced because cells with certain mutations have a selective advantage over other cells. Such an advantage would allow the mutated cells to increase in number through clonal expansion. In particular, mutations that affect the RAS pathway, which regulates spermatogonial proliferation, appear to offer a competitive advantage to spermatogonial cells, while also leading to diseases associated with<unk> <unk> . Epigenetic changes DNA methylation The production of sperm cells involves DNA methylation, an epigenetic process that regulates the expression of genes. Improper genomic imprinting and other errors sometimes occur during this process, which can affect the expression of genes related to certain disorders, increasing the offspring's susceptibility. The frequency of these errors appears to increase with<unk> . This could explain the association between<unk> <unk>  and schizophrenia.;<unk> s offspring's behavior, possibly via an epigenetic mechanism recruiting a transcriptional repressor REST. Semen A 2001 review on variation in semen quality and fertility by male<unk>  concluded that older men had lower semen volume, lower sperm motility, and a decreased percent of normal sperm. A 2014 review indicated that increasing male<unk>  is associated with declines in many semen traits, including semen volume and percentage motility. However, this review also found that sperm concentration did not decline as male<unk>  increased. X-linked effects Some classify the<unk>  as one of two different types. One effect is directly related to advanced<unk> <unk>  and autosomal mutations in the offspring. The other effect is an indirect effect in relation to mutations on the X chromosome which are passed to daughters who are then at risk for having sons with X-linked diseases.
Paternal age effect
Fetal programming
Maternal effect
Replication error phenotype
Germline mosaicism
Human genetic enhancement
Germline mutation
Structural inheritance