INTRODUCTION
Caenorhabditis elegans are nematodes that are feed on Escherichia coli. and live in free-living soil. C. elegans make good model organisms because they are small, they have a short life span, they reproduce quickly and have many offspring, they are easily and inexpensively grown in a laboratory, there is visible phenotypic differentiation between different genotypes, and there is much known about their genome. C. elegans have most major types of differentiated tissue which include; nerve, muscle, hypodermis, intestine, and gonad. C. elegans are also good to use because they can be stored in liquid nitrogen and are still viable.
C. elegans have two genders, hermaphrodite and male. The hermaphrodite has two X chromosomes. It is self-fertilizing, which means it can produce offspring without needing another C. elegans. This is supported by Current Topics in Developmental Biology when they describe the genotype (Ross Wolff & Zarkower, 2008). When the hermaphrodite C. elegans are young they produce and store sperm. When the C. elegans is older, it then produces oocyte. According to the Merriam-Webster Dictionary site, an oocyte is, an egg before it matures (Merriam-Webster). The eggs are fertilized by the sperm and go through some of their development inside the parent hermaphrodite.
C. elegans males are produced rarely in a hermaphrodite population by meiotic non-disjunction at a frequency of 0.1%. Non-disjunction is, according to the Genetics Home Reference, when chromosomes or chromatids fail to separate properly. (Genetics Home Reference) . Males have only one X chromosome. This is supported in the Developmental Biology Journal when it is stated that the hermaphrodites are XX and the males are XO (Morgan, Critte...
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...www.genetics.org/. Web. 28 Feb. 2014. .
Morgan, Dyan E., Sarah L. Crittenden, and Judith Kimble. "The C. Elegans Adult Male Germline: Stem Cells and Sexual Dimorphism." Developmental Biology 346.2 (2010): 204-14. Science Direct. Web. 28 Feb. 2014. .
"Nondisjunction." Genetics Home Reference. N.p., 25 Feb. 2014. Web. 28 Feb. 2014. .
"Oocyte." Merriam-Webster. Merriam-Webster, n.d. Web. 28 Feb. 2014. .
Ross Wolff, Jennifer, and David Zarkower. "Somatic Sexual Differentiation in Caenorhabditis Elegans." Current Topics in Developmental Biology 83 (2008): 1-39. Web. 28 Feb. 2014. .
11.2) Asexual reproduction involves a single individual / parent who pass duplicates of all its genes to its offspring without the fusion of gametes. Sexual reproduction involves two parents who give rise to offspring that have unique combination of genes inherited from the two parents.
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
6)Journal of Neuroscience, Allen, Hines, Shryne, and Gorski journal article titled "Two sexually dimorphic cell groups in the human brain."
Each chromosome carries a unique genetic code that will express itself as a particular gene. An embryo receives two sets of 23 chromosomes from the mother and father through fertilization. Every gene they inherit from the mother, they also inherit from the father. Out of both sets of 23, the embryo receives a sex chromosome, which determines its gender. The mother always gives an X to the embryo, where as the father can either give another X to create a girl or a Y to create a boy. The chromosome sets pair up, and then separate when the cell divides. One then receives different combinations of half the mother and father’s genes in their cells during development. Through these combinations, one may inherit certain genes from either the mother or father through gene dominance. They are also able to inherit genetic conditions by autosomal dominance, autosomal recessive, or sex-linked inheritance. Lastly, a child may receive a mutated or extra chromosome that codes for a genetic defect or condition. The parents would not be able to find out any of these things until after birth, which in some cases is too late to save the
From the moment sperm and egg meet, many processes begin to happen. Each of these processes are the start of forming all of the parts that make up a human being. Most people wonder if their new baby will have the eyes of the mother or the father, be tall like Grandpa or short like Aunt Kim. Be an excellent athlete like Uncle Tom or have the ability to be a rocket scientist like Grandma Sue. New parents also spend a lot of time thinking about if they will be having a boy or a girl. Twenty-two pairs of autosomes is how many it takes to form a whole homo sapien. In addition, one pair of sex chromosomes is needed. These will either be in the form of two X chromosomes to form a female or an X and a Y chromosome to form a male. This pair of sex chromosomes is responsible for much more than just the external sex organs. They control hormones, the full internal reproductive structures, and the sex discernment within the brain.
Swaab, Df. "Sexual Differentiation Of The Human Brain: Relevance For Gender Identity, Transsexualism And Sexual Orientation." Gynecological Endocrinology 19.6 (2004): 301-312. Informa Healthcare . Web. 7 Apr. 2014.
For male cats, they have a penis, prostate, scrotum (with paired testes), which all aid in creating sperm and testosterone. Additionally, the most unique feature they have is that on their penis they have little spins and barbs that hold the penis in during ejaculation.
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...
In addition to the sexes male and female, Fausto-Sterling proposes we add three more categories including herm, (a true hermaphrodite) which has both testes and ovaries, merm (a male pseudo-hermaphrodite), which has testes and no ovaries, although some aspects of female genitalia, and fem, (a female pseudo-hermaphrodite) which has ovaries and some aspects of male genitalia but no testes. The reason for the addition of these sexes is to be more accurate and inclusive for all persons. Fausto-Sterling’s arguments for having at least five sex categories are valid because only having two categories is biologically inaccurate, and exclusive to people who do not fit into either category perfectly, both contributing to societal
Most children become aware of their anatomic sex by the age of eighteen months and by three years old the child has a sense of gender identity (Rathus, Nevid, & Fichner-Rathus, 2014, p. 159). Gender identity is most consistent with chromosomal sex. There is intersexual whom possesses the gonads of one anatomic sex but external gentilia that are ambiguous or like the other anatomic sex. This is when nature and nurture comes in nature refers to the biology and nurture refers to the environmental influences. Lastly hermaphrodites are pretty rare, a hermaphrodite is a person whom has both ovarian and testicular
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...
A male makes one thousand new sperm per second, that is two trillion over a lifetime and they all are one of a kind, very unique. A woman has all her eggs from birth. The process starts out as meiosis, this is where 30,000 genes are then there are forty six chromosomes. Twenty three comes from your mother and twenty three come from your father, they only come together in meiosis in pairs, but they are not the same. Chromosomes make an exact copy of themselves then they condense making an X shape, chromosomes get a partner then embrace. The chromosomes cling close together in big chunks, the cell then divides pulling the pair apart with twenty three chromosomes. The cell alone is incomplete, but holds many promises. Every cell holds di...
Typically, XX chromosomes designate females and XY designate males, which both of these will develop into socially acceptable genders of the assigned chromosomes. Although this is mostly correct, there are some variations to the rule in which a person will differ from the assigned chromosomes and have physiological differences that will affect gender identity development. Eliza Dragowski, an assistant professor psychology, writes in a report titled Childhood Gender Identity… Disorder? Developmental, Cultural, and Diagnostic Concerns, "The second path points to anatomical brain differences. It is supported by postmortem examinations of brains of male-to-female transsexuals, which show a typical female-sized portion of the central subdivision of the bed nucleus of the stria terminal, a brain area vital in sexual behavior." This proves brain similarities between males and females, which can lead to them becoming transsexuals later in life. Their brain affects how they develop their own gender identity. Furthermore, genetic differences influence a developing identity, "review of the most recent research indicates the presence of various genetic variations that do not cause changes in reproductive anatomical structures but may produce gender-variant identities” (Dragowski). A variation of these genes will have a significant effect on gender since its part of their
Meiosis is a special type of cell division that occurs during formation of sperm and egg cells and gives them the correct number of chromosomes. Since a sperm and egg unite during fertilization, each must have only half the number of chromosomes other body cells have. Otherwise, the fertilized cell would have too many.
One of the major biological differences between males and females are hormones. Hormones that were once thought to only be important for pregnancy and sexual drive are now shown to have profound effects on just about every organ in the body.(*) Some researchers believe that higher exposure to estrogen, in females, or androgens, in males, during fetal development not only causes the sex organs to form but also predisposes the infant to behavior that is typically associated with one gender or the other. (*) For example, girls that were exposed to higher than normal prenatal levels of androgens were more likely than other females to engage in “boy-like” behavior and to play with boy’s toys eve...