Sex determination in mammalian embryos is the process by which an embryo is determined, at the cellular level, to become a male or female. At fertilization, a zygote will receive either an X or Y-chromosomes from the father’s sperm to accompany the X chromosomes given by the mothers egg. It is at this point that a zygote can be said to be male or female. However, the development of male or female sex organs is not determined until later in the sixth to seventh week of development. Genetics plays a significant role in sex determination, providing many gene loci that assist the process of cell determination and organ development.
There are two ways to describe mammalian sex determination. The first is described as primary sex determination, which is when the gonads are determined to form either the egg-forming ovaries or the sperm-forming testes. This type of sex determination is purely chromosomally influenced (Gilbert, 2014, pg. G-20). The second type of sex determination is described as secondary sex determination. This is defined as the developmental events, directed by hormones produced in the gonads, which direct the development of the phenotypes of structures outside the gonads. These structures include the ductal systems, external genitalia, and often sex-specific body size, muscle development, and vocal cartilage (Gilbert, 2014, pg. G-22). This paper will focus on events taking placing during both primary and secondary development. Discussions will first focus on when in embryonic development this determination begins to take place. Once we place the beginning of this sex determination to a specific stage in overall embryonic development, we will take a look at the specific roles the X and Y-chromosomes and their individua...
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To begin with, gender must be examined at the basic level of science in regard to physical and biological development of humans. We all understand the physical differences between the male and female gender, but how is our sex actually determined. After conception,
Sexual reproduction is that the union of male and feminine gametes to create a fertilised egg or zygote. The ensuing offspring inherit one-half their traits from every parent. Consequently, they 're not genetically similar to either parent or siblings, except within the case of identical twins. As theorised by Mendel, adults are diploid, meaning as 2N, having 2 alleles offered to code for one attribute. The gametes should be haploid, signified by N, containing just one allele in order that once 2 haploid gametes mix, they manufacture a traditional diploid individual. The method where haploid sex cells are created from diploid parents is known as meiosis, and it happens solely within the reproductive organs.
This means that all the sperm in males and eggs in females are produced from meiosis. Sperm and egg cells are haploid cells-they contain only one of each type of chromosome. Meiosis actually starts with a diploid cell that undergoes two divisions; the end products are four gametes, all genetically different. Meiosis is known as a reduction division because the daughter cells always contain half the amount of chromosomes as the diploid beginner cell. Chromosomes come in pairs and these pairs are called homologous pairs. Homologous chromosomes mean that both of the chromosomes in the pair have the same gene sequence. Human somatic cells(diploid) contain 46 chromosomes consisting of 23 homologous pairs; therefore, human gametes, which are haploid, have 23 total chromosomes-one from each homologous pair. Just like in mitosis, meiosis undergoes all of the same phases. However, because meiosis involves two divisions, the cell goes through all the phases twice. When referring to the first time the cell undergoes a phase, we say 1, and when referring to the second time, we say 2. For example, when a cell starts prophase the first time in meiosis, we say it is going through prophase 1(P1). Also, there are some differences in the process itself. During P1, homologous chromosomes exchange a section of themselves in what is known as crossing over. This provides a source of genetic variation since part of each chromosome switched places with each other, thus making both chromosomes distinct from the original. Another important difference to know is that in anaphase 1, the doubled chromosomes are not separated into sister chromatids. This doesn’t happen until A2 to ensure that each of the four gametes receives one of each kind of chromosome. There are many key points to understand about meiosis. The first being that cells in meiosis do not go through interphase twice. Interphase is a “one-time” thing; DNA
The term “intersexual” is used to describe individuals who are born with a combination of male and female genitalia, gonads, and/or chromosomes. Biologist Anne Fausto-Sterling proposed three groups of intersexuals: some with a balance of male and female characteristics, some with female genitalia but testes rather than ovaries, and some with male genitalia but ovaries instead of testes. In order to understand an individual or a community of people, anthropologists believe that by recognizing more than just female and male, it allows for a less dualistic and more holistic approach to understanding the complex relationship between biology and gender. (Guest,
Gender is determined by the sex chromosomes, XX produces a female, and XY produces a male. Males are produced by the action of the SRY gene on the Y chromosome, which contains the code necessary to cause the indifferent gonads to develop as testes (1). In turn the testes secrete two kinds of hormones, the anti-Mullerian hormone and testosterone, which instruct the body to develop in a masculine fashion (1). The presence of androgens during the development of the embryo results in a male while their absence results by default in a female. Hence the dictum "Nature's impulse is to create a female" (1). The genetic sex (whether the individual is XX or XY) determines the gonadal sex (whether there are ovaries or testis), which through hormonal secretions determines the phenotypic sex. Sexual differentiation is not drive...
The idea of the project was to experiment breeding Drosophila Melanogaster (fruit fly) to figure out if certain genes of that species were sex linked or not (autosomal). A mono-hybrid cross and di-hybrid cross was performed. For the mono-hybrid cross, white eyed female and red eyed male were placed in one vial for them to reproduce. For the di-hybrid cross, red eyed and normal winged flies and sepia eyed and vestigial winged flies were placed in their vial to reproduce. In the mono-hybrid cross the results expected were within a 1:1:1:1 ratio. Expected results similar to the expected desired null hypothesis proposed with what the F1 parental generation breeds. The potential results would have had to have been within the ratios of 9:3:3:1. The results were clear and allowed the null hypothesis to be correct. The white eyed gene in the fruit flies is sex linked. Sepia eyes and vestigial wings are not sex linked and are examples of independent assortment.
A Karyotype is when you cut out individual chromosomes from a picture and rearrange them. There are matching pairs of chromosomes these are called homologous pairs. Each pair is given a number. One of each pair came from the mother and one of each pair came from the father. The pairs can be distinguished as each pair has a distinctive banding pattern when stained. There are two sex chromosomes and the rest are called autosomes. In most karyotype the sex cells are kept to one side so that the sex can be seen easily. In females they have two X chromosomes and in the males they have an X and a Y chromosome. The Y chromosome has a portion missing and is therefore smaller then the X chromosome.
Typically males have XY chromosomes, and women have XX chromosomes; however, hermaphrodites are neither male nor female. One reason comes from Turner's Disease where the chromosomes are XO, and there is a sex chromosome missing. Another mutation is the XXY chromosomes, known as Klinefelter's Disease, which occurs in an average of one out of every 1000 births. There is also, Mosaicism, where different cells split into different parts, making up XY and XO chromosomes. Hormonal complications can change the gender...
Hettena, Seth “Study Questions ‘Sex Reassignment’” Accessed February 20, 2014. http://ai.eecs.umich.edu/people/conway/TS/HopkinsStudy.html. Leahy, A. 1935 Genetic Psychology Monographs. Nature, Nature and Intelligence.
Evolutionary developmental biology (evo-devo) was instituted in the early 1980s as a distinctive field of study to characterise the new synthesis of evolution hypothesis (Müller, 2007). Evo-devo is regarded as a new rule in evolutionary biology and a complement to neo-Darwinian theories. It has formed from the combination of molecular developmental biology and evolutionary molecular genetics; their integration has helped greatly to understand both of these fields. Evo-devo as a discipline has been exploring the role of the process of individual development and the changes in evolutionary phenotype, meaning the developmental procedure by which single-celled zygotes grow to be multicellular organisms. Alterations in the developmental program frequently cause differences in adult morphology.
In order to grasp the concept of social construction of gender, it is essential to understand the difference between sex and gender. Biologically, there are only two reproductive genital organs that are determinants of sex: the vagina and the penis. Sex is established solely through biological structures; in other words, genitalia are the basis of sex. Once a sex category is determined, gender, a human categorization socially attached to sex, is assigned based on anatomy. Gender typically references social or cultural differen...
Sex determination is decided by the 23rd pair of chromosomes commonly known as the sex chromosomes. Males have XY as their 23rd pair and females have XX. A female gamete, the ovum, can only receive only the X chromosome and the male gamete, the spermatozoon can receive either the X or the Y chromosome when meiosis occurs. Therefore the male sperm is responsible for the sex determination of the baby.
Sex and gender are terms that are mixed up from day to day and seen as similarities rather than differences. Sex is what distinguishes people from being either male or female. It is the natural or biological variations between males and females (Browne, 1998). Some of these variations are genitals, body hair and internal and external organs. It is the make-up of chromosomes, men have one X and one Y chromosome and women have two X chromosomes, these are responsible for primary characteristics (Fulcher and Scott, 2003). Gender on the other hand refers to the sociological differences between male and female. This is teaching males and females to behave in various ways due to socialisation (Browne, 1998). Example: masculinity and femininity. Girls are supposed to show their femininity by being non-competitive, sensitive, dependent, attractive and placid. If and when some girls don’t succeed in keeping this image they will be referred to as a tomboy. On the other hand, boys show their masculinity through aggression, physical strength...
Most of today’s theorists and scientists have a different perception of determining whether or not gender can be based on biological factors, or evolutionary factors. Gender determination involving humans can be identified by evaluating male and female chromosomes. Theorist of Penn State (2005) contains that chromosomes is a combination of instructions used to produce organism. As previously stated, the male chromosomes consist of X and Y. These two chromosomes are responsible for creating male gender and their ability to produce sperm. The female egg consists of double XX chromosome. Based on this theory, the X chromosomes carry a more dominant instruction manual than the Y chromosome.