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'Human genetics' describes the study of inheritance as it occurs in human beings. This article describes only basic features of human genetics; for the genetics of disorders please see: Medical genetics.

Contents

Chromosomes

Number of genes

Mitochondrial DNA

Genes and human characteristics

Genes and behavior

Genes and gender

Genes and race

Evolutionary psychology

Genetic disorders

Human traits with simple inheritance patterns

See also

References

External links

Chromosomes

Humans have 46 chromosomes, arranged in 23 pairs (i.e. they are diploid). 44 (22 pairs) of these chromosomes are autosomes, and 2 (1 pair) are sex chromosomes. Humans have an XY sex determination system, so that females have the sex chromosomes XX and the males XY. The Y chromosome is shorter than the X chromosome, so that males are hemizygous over this region. X-linked recessive genes are thus expressed more often in males. A Humans' gender is determined by the x and the y chromosomes.

Number of genes

Estimates of the number of genes humans have has been possible since DNA sequencing was first introduced. Estimates however have varied wildly, though the present best guess is 20,000-25,000, estimates of up to 40,000 have been in the past.

Mitochondrial DNA

In addition to nuclear DNA, humans (like almost all eukaryotes) have mitochondrial DNA. Mitochondria, the "power houses" of a cell, have their own DNA because they are descended from a proteobacterium that merged with eukaryotic cells over 2 billion years ago. Mitochondria are inherited from one's mother, and its DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve).

Genes and human characteristics

Genes have both minor and major effects on human characteristics. Human genes have become prominent in the nature versus nurture debate.

Genes and behavior

Genes have a strong influence on human behavior. IQ is largely heritable. However, this has been questioned. The stance that humans inherit substantial behavioral characteristics is called psychological nativism, compared to the stance that human behavior and culture are virtually entirely constructed (tabula rasa).
In the early 20th century, eugenics was policy in parts of the United States and Europe. The goal was to reduce or eliminate people whose genes were considered inferior. One form of eugenics was compulsory sterilization of people deemed mentally unfit. Hitler's eugenics programs turned social consciousness against the practice, and psychological nativism became associated with racism and sexism.

Genes and gender

The biggest genetic difference among healthy humans is in gender. Scientists debate the extent to which genes and culture affect gender roles. The case of David Reimer was once a case in point for the ''tabula rasa'' camp, though recently that same case has become evidence for a strong genetic component to gender identity.

Genes and race

Most genetic diversity occurs within races rather than between them. Common concepts of racial categories do not accurately match genetic characteristics.

Evolutionary psychology

Evolutionary psychology explains many human behaviors as more or less moderated by genes that evolved in the hunter-gatherer stage of human cultural development. See for example Stockholm syndrome.

Genetic disorders

Main articles: Genetic disorder

Humans have several genetic diseases, often caused by recessive genes. See List of genetic disorders. Genetic disorders happen everywhere and are very common in some places.

Human traits with simple inheritance patterns

'Dominant'	'Recessive'	'Reference'
Hooknose	Curled up nose	[1]
Counter-clockwise Hair Whorl	Clockwise Hair Whorl
Can Roll Tongue	Can't Roll Tongue	[2]
Widow's Peak	No Widow's Peak	[3]
Facial Dimples	No Facial Dimples	[4]
Able to taste PTC	Unable to taste PTC
Unattached earlobe	Attached earlobe
Straight thumb	Hitchhiker's thumb
Tip of pinkie bends in	Pinkie straight
Oval face	Square face
Cleft chin	No Cleft chin
Broad eyebrow	Slender eyebrow
Separated eyebrows	Unibrow
Long eyelashes	Short eyelashes
Almond eyes	Round eyes
Freckles	No Freckles
Wet-type earwax	Dry-type earwax
Left thumb on top of interlocking fingers	Right thumb on top of interlocking fingers
Clubbed thumb	Normal thumb
No wisdom teeth	Wisdom teeth	[5]

See also

★ Human evolutionary genetics

★ Human genome

★ Genetic genealogy

★ Genealogical DNA test

References

1. DOMINANT AND RECESSIVE TRAITS
2. What Are Some Traits in Your Family? Donald Galen
3. Biology, , Neil, Campbell, Benjamin Cummings, ,
4. http://www.science.edu.sg/ssc/detailed.jsp?artid=4862&type=6&root=4&parent=4&cat=40
5. http://www.helsinki.fi/science/dentgen/bg.html

External links

★ Human Genome Project

★ How many Genes do humans have?