human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.
The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.
A new era in cytogenetics, the field of investigation concerned with studies of the chromosomes, began in 1956 with the discovery by Jo Hin Tjio and Albert Levan that human somatic cells contain 23 pairs of chromosomes. Since that time the field has advanced with amazing rapidity and has demonstrated that human chromosome aberrations rank as major causes of fetal death and of tragic human diseases, many of which are accompanied by intellectual disability. Since the chromosomes can be delineated only during mitosis, it is necessary to examine material in which there are many dividing cells. This can usually be accomplished by culturing cells from the blood or skin, since only the bone marrow cells (not readily sampled except during serious bone marrow disease such as leukemia) have sufficient mitoses in the absence of artificial culture. After growth, the cells are fixed on slides and then stained with a variety of DNA-specific stains that permit the delineation and identification of the chromosomes. The Denver system of chromosome classification, established in 1959, identified the chromosomes by their length and the position of the centromeres. Since then the method has been improved by the use of special staining techniques that impart unique light and dark bands to each chromosome. These bands permit the identification of chromosomal regions that are duplicated, missing, or transposed to other chromosomes.
Micrographs showing the karyotypes (i.e., the physical appearance of the chromosome) of a male and a female have been produced. In a typical micrograph the 46 human chromosomes (the diploid number) are arranged in homologous pairs, each consisting of one maternally derived and one paternally derived member. The chromosomes are all numbered except for the X and the Y chromosomes, which are the sex chromosomes. In humans, as in all mammals, the normal female has two X chromosomes and the normal male has one X chromosome and one Y chromosome. The female is thus the homogametic sex, as all her gametes normally have one X chromosome. The male is heterogametic, as he produces two types of gametesone type containing an X chromosome and the other containing a Y chromosome. There is good evidence that the Y chromosome in humans, unlike that in Drosophila, is necessary (but not sufficient) for maleness.
Britannica Quiz
Genetics Quiz
A human individual arises through the union of two cells, an egg from the mother and a sperm from the father. Human egg cells are barely visible to the naked eye. They are shed, usually one at a time, from the ovary into the oviducts (fallopian tubes), through which they pass into the uterus. Fertilization, the penetration of an egg by a sperm, occurs in the oviducts. This is the main event of sexual reproduction and determines the genetic constitution of the new individual.
Human sex determination is a genetic process that depends basically on the presence of the Y chromosome in the fertilized egg. This chromosome stimulates a change in the undifferentiated gonad into that of the male (a testicle). The gonadal action of the Y chromosome is mediated by a gene located near the centromere; this gene codes for the production of a cell surface molecule called the H-Y antigen. Further development of the anatomic structures, both internal and external, that are associated with maleness is controlled by hormones produced by the testicle. The sex of an individual can be thought of in three different contexts: chromosomal sex, gonadal sex, and anatomic sex. Discrepancies between these, especially the latter two, result in the development of individuals with ambiguous sex, often called hermaphrodites. Homosexuality is unrelated to the above sex-determining factors. It is of interest that in the absence of a male gonad (testicle) the internal and external sex anatomy is always female, even in the absence of a female ovary. A female without ovaries will, of course, be infertile and will not experience any of the female developmental changes normally associated with puberty. Such a female will often have Turner syndrome.
Are you a student? Get Britannica Premium for only $24.95 - a 67% discount!
If X-containing and Y-containing sperm are produced in equal numbers, then according to simple chance one would expect the sex ratio at conception (fertilization) to be half boys and half girls, or 1 : 1. Direct observation of sex ratios among newly fertilized human eggs is not yet feasible, and sex-ratio data are usually collected at the time of birth. In almost all human populations of newborns, there is a slight excess of males; about 106 boys are born for every100 girls. Throughout life, however, there is a slightly greater mortality of males; this slowly alters the sex ratio until, beyond the age of about 50 years, there is an excess of females. Studies indicate that male embryos suffer a relatively greater degree of prenatal mortality, so the sex ratio at conception might be expected to favour males even more than the 106 : 100 ratio observed at birth would suggest. Firm explanations for the apparent excess of male conceptions have not been established; it is possible that Y-containing sperm survive better within the female reproductive tract, or they may be a little more successful in reaching the egg in order to fertilize it. In any case, the sex differences are small, the statistical expectation for a boy (or girl) at any single birth still being close to one out of two.
During gestationthe period of nine months between fertilization and the birth of the infanta remarkable series of developmental changes occur. Through the process of mitosis, the total number of cells changes from 1 (the fertilized egg) to about 2 1011. In addition, these cells differentiate into hundreds of different types with specific functions (liver cells, nerve cells, muscle cells, etc.). A multitude of regulatory processes, both genetically and environmentally controlled, accomplish this differentiation. Elucidation of the exquisite timing of these processes remains one of the great challenges of human biology.
Read the original here:
Human genetics | Description, Chromosomes, & Inheritance
- Mating Study Unlocks the Genetic Code of Attraction - Neuroscience News - March 18th, 2024
- Mindfulness in your DNA? Capacity to be present is partly a function of genetics, study finds - PsyPost - March 18th, 2024
- Genetic testing scam targets Medicare recipients, including those in Spokane - KXLY Spokane - March 18th, 2024
- Some people are genetically predisposed to gain weight. These 5 tips can help - CNN - March 18th, 2024
- SOPHiA GENETICS and The French Kidney Cancer Research Network (UroCCR) Publish Results from Multiyear ... - PR Newswire - March 18th, 2024
- Tissue samples show the deep genetic and cellular impacts of smoking - Medical Xpress - March 18th, 2024
- The regulatory landscape of chromatin accessibility - Nature.com - March 18th, 2024
- Genome assemblies of 11 bamboo species highlight diversification induced by dynamic subgenome dominance - Nature.com - March 18th, 2024
- Research reveals the genetic code behind non-identical twins - Medical Xpress - March 18th, 2024
- How genetic therapies transformed the lives of sickle cell patients - KPVI News 6 - March 18th, 2024
- The Next Wave of Privacy Litigation: The Illinois Genetic Information Privacy Act - Perkins Coie - March 18th, 2024
- State initiates study on genetic cancers, Lynch Syndrome - The Times of India - March 18th, 2024
- How genetic therapies transformed the lives of sickle cell patients - Citizentribune - March 18th, 2024
- Dr Plichta on Areas of Interest for Genetic Testing Research in Breast Cancer - OncLive - March 18th, 2024
- The Genetic History of the Jews Mosaic - Mosaic - March 18th, 2024
- New insights into genetic mechanisms could improve treatment of liver fibrosis - Medical Xpress - March 18th, 2024
- 5 Questions To Ask About The Ethics Of Genetic Data - Forbes - March 18th, 2024
- Couple raising money to fix sons club feet caused by rare genetic condition - 21 Alive News - February 18th, 2024
- What can bulls tell us about men? Genetic discovery could translate to human fertility research - Medical Xpress - February 18th, 2024
- Legislation seeks to bar life insurance companies from purchasing recreational genetic testing data - Delaware First Media - February 18th, 2024
- Family-based study identifies potential new genetic factors linked to Alzheimer's risk in people with African ancestry - National Institute on Aging - February 18th, 2024
- Genetic determinants of micronucleus formation in vivo - Nature.com - February 18th, 2024
- Near-gapless and haplotype-resolved apple genomes provide insights into the genetic basis of rootstock-induced ... - Nature.com - February 18th, 2024
- Accurate and sensitive mutational signature analysis with MuSiCal - Nature.com - February 18th, 2024
- CRISPR, the Genetic Revolution of the 21st Century | OpenMind - BBVA OpenMind - February 18th, 2024
- Genetic control of thermomorphogenesis in tomato inflorescences - Nature.com - February 18th, 2024
- Natural selection and genetic diversity maintenance in a parasitic wasp during continuous biological control application - Nature.com - February 18th, 2024
- Understanding how natural genetic variation contributes to adaptive responses to low oxygen - News-Medical.Net - February 18th, 2024
- Division of Epidemiology and Genetics - Epidemiology and Genetics - University of Southern California - February 18th, 2024
- Genetic study clarifies the link between birth weight and adult morbidity - Medical Xpress - February 18th, 2024
- AI and genetics underpin project to speed up CVD diagnosis and personalise treatment - Hospital Healthcare - February 18th, 2024
- Study Reveals Complex Interaction Between Genetics and Environment in Brain Functioning - Medriva - February 18th, 2024
- Unraveling the Impact of Genetics and Socioeconomic Status on Behavioral and Psychiatric Traits - Medriva - February 18th, 2024
- Genetic Investigation Reveals CETP Gene Variants Linked to Cardiovascular Resilience in Genome-Wide Association ... - Physician's Weekly - December 30th, 2023
- Raha Kapoor's blue eyes remind fans of her great-grandfather, Raj Kapoor; here's what genetics says - IndiaTimes - December 30th, 2023
- Genetic clue to pericarditis inflammation points to promising new treatments - News-Medical.Net - December 30th, 2023
- Certain genetic predispositions may increase risk of atrial fibrillation among those with high alcohol consumption - 2 Minute Medicine - December 30th, 2023
- Understanding the genetic basis of hereditary diffuse gastric cancer - News-Medical.Net - December 30th, 2023
- Genetic engineering was meant to save chestnut trees. Then there was a mistake. - The Washington Post - December 30th, 2023
- Unraveling the mystery of hereditary diffuse gastric cancer - EurekAlert - December 30th, 2023
- What is Genetics? | AMNH - American Museum of Natural History - December 22nd, 2023
- Who killed Shelley Connolly? Genetic genealogy leads authorities to a suspect and a conviction - Alaska's News Source - December 22nd, 2023
- C.S. Lewis, Atheism, and the Genetic Fallacy - Word on Fire - December 22nd, 2023
- FDA approves first genetic test to assess opioid addiction risk using DNA sample - Fox News - December 22nd, 2023
- Genetic blueprint of wild grapes could help breed better grapes - University of California, Davis - December 22nd, 2023
- Unlocking the genetic secrets of grape seedlessness - Phys.org - December 22nd, 2023
- Unlocking the genetic secrets of drought resilience in Persian walnuts - Phys.org - December 22nd, 2023
- FDA approves genetic test to assess patients risk of developing an opioid addiction - KXAN.com - December 22nd, 2023
- How researchers are CReATiNG synthetic chromosomes faster and cheaper - EurekAlert - December 22nd, 2023
- The promise of genetic therapies in sickle cell disease - The Lancet - December 22nd, 2023
- Assessment of genetic diversity, population structure and wolf-dog hybridisation in the Eastern Romanian Carpathian ... - Nature.com - December 22nd, 2023
- Genetics and Heart Disease: What you need to know - IndiaTimes - December 22nd, 2023
- How to become a geneticist - University of Sydney - December 22nd, 2023
- Study sheds light on the ancestry and genetics of Coast Salish woolly dogs | News | Vancouver Island University ... - Vancouver Island University News - December 22nd, 2023
- BASIC GENETICS INFORMATION - Understanding Genetics - NCBI Bookshelf - December 13th, 2023
- Introduction to Genetics - Open Textbook Library - December 13th, 2023
- Clues to preventing Alzheimer's come from patient who, despite genetics, evaded disease Washington University ... - Washington University School of... - December 13th, 2023
- Environmental stress rather than genetics influenced height differences in early Neolithic people: Study - Phys.org - December 13th, 2023
- What is trisomy 18? Why the fatal genetic disorder is in the news and what it's like to get the diagnosis. - Yahoo Life - December 13th, 2023
- Spanish scientists identify the molecular mechanisms controlling the genes involved in proper formation of the heart ... - EurekAlert - December 13th, 2023
- GENEFIT, the First-Ever Fitness Technology to Integrate Personal Genetics with Wearable Tracker Data, Launches to ... - Fitt Insider - December 13th, 2023
- Genetic 'protection' against depression was no match for pandemic stress, finds study of first-year college students - Medical Xpress - December 13th, 2023
- Origin and evolution of the triploid cultivated banana genome - Nature.com - December 13th, 2023
- CellCharter reveals spatial cell niches associated with tissue remodeling and cell plasticity - Nature.com - December 13th, 2023
- How do we get our eye color? A genetics expert reveals the fascinating truth - Fox News - December 13th, 2023
- WVU Today | WVU scientists spice up genetic research through habanero peppers and AI - WVU Today - December 13th, 2023
- Genetic mutations that promote reproduction tend to shorten human lifespan, study shows - Phys.org - December 13th, 2023
- Stanford Scientists Discover Common Genetic Factor That Fends Off Alzheimer's and Parkinson's - SciTechDaily - December 13th, 2023
- Association of genetic risk and lifestyle with pancreatic cancer and their age dependency: a large prospective cohort ... - BMC Medicine - December 13th, 2023
- New bill would block American genetic data from access by companies tied to foreign adversaries - Homeland Preparedness News - December 13th, 2023
- Electric Eels Shocking Ability To Alter The Genetics Of Nearby Animals - Forbes - December 13th, 2023
- "When them genetics kick in its all over" - NBA fans send in rib-tickling reactions as LeBron James attends Zhuri James' volleyball game -... - October 16th, 2023
- David Liu, chemist: We now have the technology to correct misspellings in our DNA that cause known genetic diseases - EL PAS USA - April 7th, 2023
- World Health Day 2023: Understanding the science of Epi-genetics and how to apply it in our daily lives - Free Press Journal - April 7th, 2023
- Genetics - National Institute of General Medical Sciences (NIGMS) - March 29th, 2023
- GENETICS 101 - Understanding Genetics - NCBI Bookshelf - March 29th, 2023
- People always think Im skinny because of good genetics theyre shocked when they see what I used to lo... - The US Sun - March 29th, 2023
- Forensics expert explains 'genetic genealogy' process believed to be used in Kohberger's arrest - KTVB.com - January 6th, 2023
- Idaho student murders: What is genetic genealogy, a tool reportedly used to help capture the suspect? - FOX 10 News Phoenix - January 6th, 2023
- What is a Genetic Counselor and How Can They Help You Navigate Your Healthcare Journey? - ABC4.com - December 3rd, 2022
Tags: