Example of male and sex-specific Development of the Human Brain PDF anatomy from front and back. Sex differences in human physiology are distinctions of physiological characteristics associated with either male or female humans. These can be of several types, including direct and indirect. Direct sex differences follow a bimodal distribution.
Författare: Susanne Neufang.
With the emergence of non-invasive methods like magnetic resonance imaging (MRI) and functional MRI (fMRI), there is growing evidence of maturational changes in both neuro-anatomical structures and neural activation patterns. Developmental changes have been shown to last until adolescence. In study 1, we examined the impact of steroids on the developing brain and found that amygdala and hippocampal as well as parietal volumes were associated with circulating testosterone levels. In the studies 2 to 5 we adressed differences in brain activation patterns of attention between children and adults, where children were either normally developing children or children with ADHD. We found differences in the developmental trajectories in the fronto-striatal pathway between children with and without ADHD, as well as an increase in brain connectivity in a fronto- parietal network with adolescence. We conclude, that the puberty might have organizational effects on the developing human brain, which manifests itself in both, brain structure and function.
The complementary result for the X-chromosome follows, either a double or a single X. Indirect sex differences are general differences as quantified by empirical data and statistical analysis. The Human Y Chromosome showing the SRY gene. SRY is a gene which regulates sexual differentiation. One set of 23 comes from the mother and one set comes from the father. Of these 23 pairs of chromosomes, 22 are autosomes, and one is a sex chromosome.
Sperm also have only one set of 23 chromosomes and are therefore haploid. The sex chromosome in a human egg is always an X chromosome, since a female only has X sex chromosomes. In sperm, about half the sperm have an X chromosome and half have a Y chromosome. If an egg fuses with a sperm with a Y chromosome, the resulting individual is male. If an egg fuses with a sperm with an X chromosome, the resulting individual is female. There are rare exceptions to this rule in which, for example, XX individuals develop as males or XY individuals develop as females.
The X-chromosome carries a larger number of genes in comparison to the Y-chromosome. In humans, X-chromosome inactivation enables males and females to have equal expression of the genes on the X-chromosome since females have two X-chromosomes while males have a single X and a Y chromosome. This process is seen in all mammals and is also referred to as lyonisation —after the geneticist Mary F. Lyon who described the process in 1962.
In the somatic cells of a developing female child, one of the X-chromosomes is shortened and condensed. The genes on this chromosome therefore can not be transcribed into an mRNA transcript and remain unread. For information about how males and females develop differences throughout the lifespan, see sexual differentiation. Sexual dimorphism in humans is the subject of much controversy, especially relating to mental ability and psychological gender. For a discussion, see biology of gender, sex and intelligence, gender, and transgender.