Summary

Summary

The field of genetics studies how children inherit traits from their parents and relatives as determined by DNA. While a karyotype is a representation of a person’s chromosomes, his or her complete genetic complement is the genome. The combination of varying forms of genes, called alleles, makes up a person’s genotype. When an allele pair is identical, the individual is homozygous for that trait. When alleles are different, the individual is heterozygous. A genotype is the actual genetic makeup of cells. A phenotype is the way in which these genes are expressed. Genetic variation occurs because of inde-pendent assortment, homologue crossover, and random fertilization.

Patterns of inheritance through families are called modes of inheritance, which include autoso-mal recessive, autosomal dominant, and X-linked recessive. Genetic disorders usually reflect homozy-gous recessive conditions. Carriers are heterozygotes that do not express a trait but can pass it to their offspring. Traits determined by genes on the X and Y chromosomes are called “sex-linked traits.” Gene expression can be influenced or overridden by envi-ronmental factors. Inheritance may be determined by factors other than nuclear DNA sequence, which include protein-­coding genes, RNA-only genes, and epigenetic marks. Advances in genetics, including the outstanding results of the Human Genome Proj-ect, are improving treatments and even cures for a large variety of diseases and disorders linked to gene and chromosomal defects. Procedures used to check for genetic conditions include pedigrees, amniocen-tesis, CVS, and blood tests.