Sexual Selves and Development

Sexual Selves

• Being male or female is important in relationships, thoughts, actions, and how others see them.
• Gender is dictated by genes, but also influenced by psychological and sociological factors.
• Maleness or femaleness is determined at conception with males inherit an X and a Y chromosome and females inherit two X chromosomes.
• Hormones control the development of reproductive structures.
• Biological factors and social cues influence sexual feelings.

Sexual Development

• Gender differences become apparent around the ninth week of prenatal development.
• All embryos develop two unspecialized gonads in the fifth week, which can become testes or ovaries.
• Indifferent gonads form near two sets of ducts that offer two developmental options.
• Müllerian ducts develop into female sexual structures if they continue to develop.
• Male structures are formed if the Wolffian ducts persist.
• The choice to follow a male or female developmental pathway occurs during the sixth week by sex chromosome constitution and certain genes.
• The SRY gene on the Y chromosome, when activated, guides development on a male route with hormones.
• In the absence of SRY activation, a female develops.
• Sex determination is now seen as a fate imposed on precursor structures.

Sex Chromosomes

• Human males and females have equal numbers of autosomes.
• Males have one X and one Y chromosome, while females have two X chromosomes.
• The heterogametic sex has two different sex chromosomes.
• Having two of the same sex chromosome is the homogametic sex.
• Sex chromosomes differ in size and gene content; the X chromosome has more than 1000 genes while the Y chromosome has 231 protein-encoding genes.
• The Y chromosome structure consists of a short and long arm with pseudoautosomal regions PAR1 and PAR2 at both tips.
• The pseudoautosomal regions comprise 5 percent of the chromosome and include 63 pseudoautosomal genes.
• DNA sequences have counterparts on a chromosome and can cross over.
• The Y chromosome was first seen under a light microscope in 1923 and researchers recognized its association with maleness.
• Researchers looked to identify the gene or genes that determine the sex.
• In 1990, researchers isolated and identified the SRY gene.
• Clues came with the interesting people with two x chromosomes who developed as men known as (XX male syndrome) and women with one X and one Y chromosome who developed as women known as (XY female syndrome).
• The SRY gene encodes a protein called a transcription factor.
• The SRY transcription factor stimulates male development by sending signals to the indifferent gonads.
• Sertoli cells secrete the anti-Müllerian hormone, destroying potential female structures.
• Interstitial cells in the testis also secrete testosterone, stimulating the development of male structures.
• Prenatal sexual development is a multistep process where genetics can intervene.
• An XY individual with a blocked gene and hormone-controlled male structure may have a female phenotype.
• Several terms describe individuals whose genetic/chromosomal sex and physical structures are inconsistent with one gender
• These include: -Hermaphroditism being an older term for someone with both male and female sexual structures -Intersex describing individuals with inconsistent internal and external structures, or ambiguous genitalia, and -Pseudohermaphroditism being the presence of both types of structures at different stages of life.
• A transgender individual has the phenotype and sex chromosomes of one gender but strongly identifies with the opposite gender.

Homosexuality

• No one really knows why feelings of gender belonging or attraction exist however, they are very strong.
• Homosexuality occurs when a person's phenotype and genotype are consistent, but physical attraction is toward the same sex.
• It is seen in cultures and has been documented in over 500 animal species.
• Homosexuality reflects complex input from both genes and the environment.
• The genetic influence has been suspected because homosexual individuals have strong feelings at being young children long before knowing the term.
• Identical twins are more likely to both be homosexual than fraternal twins which suggests a genetic component.

Sex Ratio

• The sex ratio in a population is the proportion of males to females.
• It is calculated by dividing the number of males by the number of females, multiplied by 1,000.
• A sex ratio of equal numbers of males and females would be 1,000.
• Sex ratio at birth is termed secondary while at maturity it is tertiary.
• India and China researchers identified "missing females".
• XX fetuses that were terminated and underreporting of female births, along with infanticide caused sex ratios favoring males.
• By 2020, 20 million found themselves without female partners as a consequence of China's "one-child policy with financial incentives to control runaway population growth which began in 1979.
• The government revoked benefits if a couple had a second child.
• Families wanted their only child to be a boy, and failed to continue or report female pregnancies and there was societal reasoning where a son would care for his aging parents, but a daughter would care for her in-laws.
• The one-child policy prevented hundreds of millions of births.
• The average number of births per woman fell from 5.4 in 1971 to 1.8 in 2001.
• By the turn of the century, 117 boys were being born for every 100 girls.
• As a result, Children have few siblings, cousins, aunts, or uncles.
• Human females are XX, and males are XY.
• The Y chromosome has few genes including palindromes and sequences similar to those on the X chromosome.
• The activation of SRY starts gene action that causes testes to develop.
• Testosterone directs the development of external structures.
• Disorders can cause chromosomal, gonadal, and/or phenotypic sex to be inconsistent.
• Genes and the environment contribute to homosexuality.
• Traits passed on the Y chromosome are Y-linked and those on the X-chromosome are X-linked
• Males are hemizygous, expressing all genes on their X chromosome, whereas females express recessive alleles on the X chromosome only if they are homozygous recessive
• X-linked recessive traits have a 50 percent probability of passing from carrier mothers to sons.
• Mendel’s first law can be used to solve problems involving X linked genes.

Sex-Linked vs Sex-Influenced Traits

• An X-linked recessive trait is generally more prevalent in males than females,
• Sex-limited traits affect structures or functions that are present in only males or only females and the gene may be X-linked or autosomal.
• Animal breeding requires understanding sex-limited inheritance.
• In humans, beard growth is sex-limited; women does not manufacture hormones that produce facial hair.
• Preeclampsia can arise during pregnancy is obviously sex-limited, but the male genome contributes to the development of the placenta.
• A study found if a man's first wife had Preeclampsia, his second wife had double the risk and women whose mothers-in-law developed Preeclampsia when pregnant had twice the rate of developing it.

X-Inactivation

• Females have two alleles where males have only one.
• X inactivation balances the expression of genes on the X chromosome
• A female expresses X chromosome genes from her father in some cells and from her mother in others and is a mosaic for expression of most genes on the X chromosome.
• The inactivated X chromosome is called a Barr body.
• X inactivation occurs early in development an is an epigenetic change that does not alter the DNA base sequence.
• The XIST gene controls X inactivation.
• The impact of X inactivation on the phenotype is
  • Homozygous X-linked genotypes have no effect because no matter which X chromosome is turned off, the same allele is left to be expressed.
  • Heterozygotes lead to expression where one allele is the result.
• Incontinentia pigmenti patients can reveal the X inactivation.
• Heterozygous females for an X-linked recessive gene can express the associated condition of the normal allele is inactivated in tissues that are affected.
• A carrier who expresses the phenotype is called a manifesting heterozygote.
• In humans:X inactivation can identify Lesch-Nyhan carriers.One result of that is cerebral palsy, biting fingers etc and mutation with defective or absent HGPRT, an enzyme.
• One of a female's has the X inherited form their father, while the other population has the X chromosomes she inherited.
• Differences can lead to advantages for women, as displayed with certain monkeys being able to enjoy tri color vision when they are heterozygous for X-linked vision pigment genes.

Genomic Imprinting

• Methyl (CH3) groups cover a gene preventing them being accessed to synthesize protein.
• Both copies copied inherited are methyl covered, in every individual, and the parental mutant is transferred.
• Imprinting doesn't occur through meiosis however; in females it occurs at both XY and XX.
• Understanding comes from seeing human development early on. It can explain how the fetus develops and the reason for the placenta. The discovery was made in mouse embryos.
• Genomic imprinting explains in incomplete penetrance, in which one inherits a genotype associated with is known as inheritance.
• Also important with assisted technologies for fertility, in manipulations such as IVF.

Imprinting Disorders

• There were 156 identified affect health when.
• Effects of are revealed only when the other allele doesn't exist.
• Angelman has similar features, such as autism. Only the mother's chromosome 15 region is in prader-willi syndrome, while the reverse happens in a angelman.
• May be from Alzheimers or for autism. Also is a genetic contribution. Also can lead to a one parent only genetic profile.