Pros and Cons of Asexual and Sexual Reproduction - Assignment Example

Name: University: Science of Sex – Weekly Homework Blog Topic #1: Why have sex? Question 1: Advantages and disadvantages of asexual and sexual reproduction i. Asexual reproduction Advantages a) Enables quick reproduction and colonization b) No mates are needed c) During an emergency, organisms can stay alive to produce other organisms d) Requires less energy and is environmentally friendly Disadvantages a) There is no diversity b) Prone to extinction due to struggle for existence c) Organisms have inability to adapt to environment changes d) Genetic mutation can be harmful to the offspring ii. Sexual reproduction Advantages a) Through natural selection, harmful mutations are removed from the population b) There is variation in offspring which creates diversity c) It can allow multiple reproduction of offspring d) Offspring have unique genetics that allow for adaptation Disadvantages a) Require mating, this needs time and energy b) The rate of reproduction is slower c) It is not guaranteed that reproduction will occur Question 2: Why can parthenogenesis in the whiptail skink be considered a degenerate form of reproduction? Some species of whiptail skink lizards do not need male fertilization to reproduce. Only females are present in the population (genetic isolation) and reproduction occurs when another female mimics a male’s role in courtship. This means that there is no exchange of genetic material, which is a disadvantage if changes occur to the environment. Unless there is recombination of DNA, the offspring produced will have identical chromosomes in these parthenogenetic species, meaning that genetic weakness such as physical mutation and susceptibility to diseases will have a greater chance. D1: Describe several different hypotheses for why sexual reproduction evolved. How do you think some groups of rotifers have managed to exist for millions of years without sex? Red Queen Hypothesis In this hypothesis, it is proposed that an organism must be under constant adaptation, evolution, and proliferation in order to gain reproductive advantages. The organism should be able to survive when subjected to ever-evolving opposing surrounding organisms in an environment that is ever changing. The hypothesis explain two phenomena: the advantages of sexual reproduction at individual levels, and the constant extinction rates caused by co-evolution of competing species as examined in paleontological records. Mutational deterministic hypothesis In this hypothesis, when deleterious mutants act in a synergistic manner, negative disequilibrium will persist in infinite species populations with respect to deleterious mutation i.e. a group of deleterious mutants will lead to a greater detriment the fitness of an individual if they acted in an independent manner. This causes evolution of higher levels of recombination. Selection interference hypothesis This hypothesis argues that there is an additional evolution of sexual signals as a way of male organisms to hinder the choice of a female mate through interference of propagation and reception of sexual signals from other males. Some species of rotifers have managed to exist for millions of years without sex by producing eggs with genetic clones of the females – no males in the population. They survive by evolving into distinct species by developing adaptations to different environmental conditions. Natural selection has resulted into divergence of distinct entities equivalent to sexual reproduction. Topic #2: Human Reproductive System CT 1: How could you redesign the male reproductive system so that the path of urine and the path of sperm are separate? In men, the urine tube from the bladder can be relocated from the urethra to an opening near the pubic bone, such that urine is delivered from these opening and leaving the urethra only for sperms. CT 2: Animals that reproduce in water typically do not have a penis. What advantage does a penis serve for humans, who reproduce on land? The penis has what disadvantage? Advantages a) Used to discharge and transfer spermatozoa into the female vagina b) Flexible, which allow a variety of copulation positions. c) Ability for internal fertilization by direct delivery of sperms Disadvantages a) Sexual partners have to meet and have a physical sexual contact b) The penis is vulnerable to injury by virtue of its location outside the body CT 3: How could you redesign the female reproductive system so that the vagina is not both the organ of copulation and the birth canal? A female reproductive system can be re-designed to have a different birth canal and leave the vagina for copulation by creating an opening near the pelvic bone. As the offspring nears the delivery period, the hip ligaments loosen to allow child birth. As a result of this redesign, the uterus will be made in such a way that the offspring lies in a tilted position towards the pelvic bone. CT 4: Following menopause, females stop producing eggs and cannot get pregnant. Males produce sperm their entire lives. Relate this discrepancy to differences in the reproductive function and expected behaviour of the sexes. Male fertility persists until a very late age compared to females who reach the menopause earlier and stop reproducing. The testes will continue producing sperm, although the rate of sperm production may fall but the fertility remains. In women, the quantity and quality of egg reduces with age to a point where no egg can be produced anymore. These changes are due to ovarian changes, fallopian tube changes, and uterine changes. Sexual desire as well as sexual response in men continue into a later age compared to their female counterparts who have lesser sexual desires and response. Topic #3: Human Sexual Response Question 1: The Masters and Johnson model of human sexual response has how many phases? What are they? There are four phases in this model: Excitement phase – Initial arousal Plateau phase – Full arousal due to continued stimulation, yet to orgasm Orgasm phase – after plateau phase Resolution phase – after orgasm Question 4: How do men and women differ with regard to sexual arousal? In women, sexual arousal increases blood flow through the genital region. The vaginal walls become lubricated with a fluid. The clitoris enlarges and hardens as a result of increased blood flow, and becomes more conspicuous and sensitive to touch. Continued stimulation makes the outer parts of the vagina to tighten, reducing the size of the opening. Closer to reaching an orgasm, the clitoris retracts and becomes less conspicuous. For men, the penis becomes erect due to increased blood flow which fills the spongy tissue. The blood flow inserts pressure in veins to keep the penis erected. Continued arousal hardens the tip of the penis, producing a clear fluid through the urethra. Men take little time to get aroused than women, but most importantly, the pace of sexual arousal varies from individual to individual. Question 6: Discuss three controversies about female sexual response Clitoral and vaginal orgasm – It is established that orgasm is the same regardless of the area of stimulation. The only thing that can vary is the intensity of orgasm. Nevertheless, the clitoris is much more sensitive to sexual stimulation compared to the vagina, which makes it more effective in women stimulation and orgasm. i. The G-spot – This is a sensitive area in the front part of the vagina with several nerve endings. It is alleged that during stimulation, the G-spot swells and the spongy tissue is filled with blood. As to whether it exists or not, it is controversial. ii. Ejaculation – There is a current debate on whether females ejaculate or not i.e. release of a fluid during orgasm. The fluid is believed to come from the Skene’s glands or female prostate, located on either side if the female urethra. CT2: Women are more apt to see sexual desire as a means to love, emotional intimacy, or physical closeness. Is this goal consistent with the female’s role of bearing children? Why? This goal may be said to be consistent with a woman’s role to bear children even though sexual desire is an important factor in strengthening romantic relationships. It is true that women seek a premium sense of love, emotional intimacy, and physical closeness with their sexual mates. Sex with several people does not give a woman more potential genetic offspring. In addition, women’s orgasm is less reliable compared to men’s, reducing the odds of enjoying casual sex. Women will choose their sexual partners to and know them better to increase chances of enjoyment and reduce chances of harm. From this logic, women are bio-programmed to seek for stable and intimate relationships to get aroused – hence, made for sexual monogamy, marriage and child bearing. Topic #4: Animal mating systems Question 1: Why is polyandry uncommon? What sorts of ecological and phylogenetic circumstances might favor polyandry in animals? Polyandry is uncommon because of the nature of human psychology – most people would not like sharing their sexual partners. Ecological and phylogenetic circumstances that might favor polyandry in animals include lower male mating opportunities, fertility assurance, and sexual selection. Question 2: The graph on page 341 shows the relationship between harem size, or the number of females that a male monopolises, and the ratio of male-to-female body length, a measure of sexual dimorphism, in a variety of species of seals. A: What is the most likely cause of this relationship? This relationship is caused by a male’s response to sexual selection. B: What prediction could you make about the breeding habitat occupied by a species at the lower left of the curve versus one at the upper right? The species in the upper right corner have a rich breeding habitat with more resources available, compared to the species at the lower left side. Environmental conditions in the habitat are also likely to be better compared to the others. Availability of resources reduces competition with other organisms. Topic #5: Sexual selection Question 2: When we see differences between the sexes, we usually assume that they have come about by sexual selection. Can you think of selection pressures other than obtaining mates that might produce such differences? Other selection pressures include increasing fertilization success, parental care of offspring, morphological structures, and signals (chemical, acoustic and visual). Question 3: Males typically compete for access to females and often obtain more than one mate, while females are particular about their choice of mates. In some species, however, the male supplies the female with large “gifts” in the form of captured prey or large, protein-rich sperm packets. What differences might you expect to see in the reproductive behaviour of such species when compared with the typical pattern? Females feeding on large amount of gifts lay more eggs compared to other females. The males with larger gifts have a longer mating time, fertilizing more eggs. In some cases, gifts increase the female’s longevity. A: Name and describe the hypotheses proposed to explain the evolution of sexually dimorphic traits. The two hypotheses are handicap principle and the sexy son hypothesis Sexy son theory This evolutionary theory states that an ideal mate choice for a female among other potential male mates is one with genetic genes will produce a male offspring with the highest chance of reproductive success. This implies the capacity of a potential mate to be a parental caregiver, or provide direct benefits such as gifts, good territory or nuptial gifts from father to the mother which are of potential value as father to the offspring of the female. Handicap hypothesis This theory explains how evolution of dimorphic traits may lead to reliable or honest signaling between organisms with an obvious motivation deceive or bluff each other. In this theory, also referred to as the handicap principle, reliable signals are costly to the signaling organism, costing it something that other individuals cannot afford due to a missing trait. Reference Read More