sex and reproduction Flashcards
(18 cards)
what is asexual repro?
Individuals produce genetically identical copies of itself = essentially clones. If parents are well adapted to an environment, and that environment is stable, then the cloned offspring with all be well adapted also.
what is sexual repro?
Production of offspring that differ in genetic make-up from parents. Allows for variation(crossing over) within a species. This is important for evolution as it allows species to adapt to changing environments, which includes emerging infectious diseases.
Several different forms of asexual reproduction in animals: what is budding and what are the two types?
An unequal division of an animal’s body. For example, Sponges can produce internal buds, referred to as gemmules. Gemmules are a collection of cells within the body of a sponge. The parent body disintegrates, and new sponges, genetically identical to the parent and to each other, are formed from the gemmule cells. Other animals produce External Buds. Small groups of cells pinch off from a parent. For example, this can happen in many cnidarians, such as hydra.
Several different forms of asexual reproduction in animals: what is fragmentation?
An individual breaks up into multiple parts. Each part is capable of developing into a new individual. This occurs in several groups of animals, including flatworms and echinoderms.
Several different forms of asexual reproduction in animals: what is parthenogenesis?
Eggs are produced, but do not undergo crossing over or recombination. They are activated without being fertilized; therefore, they develop into clones of the mother.
describe sexual repro?
it involves the fusion of gametes and therefore requires meiosis. The reduction division in meiosis ensures that the chromosome number of the gametes is halved from that of body cells. When the gametes fuse, the ploidy number (number of chromosome sets) is restored, rather than doubling each generation.
sexual reproduction: what is isogametes?
In primitive forms of sexual reproduction, you cannot distinguish female and male individuals. The gametes produced are of equal size = isogametes, or same-sized gametes. If isogametes are produced, then no male or female is recognized. Isogametes are exactly alike in all characteristics. They are motile and seek out each other, fuse, and form a zygote. No living animals species are known to produce isogametes (many algae, as do several groups of fungi). Also, the first groups of eukaryotes are thought to have produced isogametes, and all unicellular eukaryotes are isogametic.
sexual repro: what are macrogametes, microgametes, gonads, what do the ovaries and testes produce?
large gametes are called macrogametes = eggs; and the smaller gametes are microgametes = sperm. Typically, sperm are motile and seek out eggs, which are non-motile. The gametes are produced in specialized organs referred to as gonads. The gonads that produce eggs (technically ova) are the ovaries; whereas, spermatozoa are produced in testes.
sexual repro: what is dioecious and monoecious?
Ovaries and testes can be found in separate individuals (dioecious), or in the body of one individual (monecious = hermaphrodites). Typically, monoecious individuals do not self-fertilize. For example, many species of earthworms are monecious, and during copulation, sperm are transferred from each individual into the mate—any individual of that species encountered can be mated.
what is external fertilization? (gametogenesis) how is it coordinated? what does the coordinating?
fertilization occurs outside of the body. produce large quantities of eggs. Obviously there has to be some mechanism to coordinate the release of gametes. Gametogenesis (formation of gametes) is regulated by environmental factors or stimuli—such as change in day length, change in temperature, etc., therefore, we recognize breeding seasons. In vertebrates, this coordination occurs through the hypothalamo-hypophyseal axis we discussed earlier in in the week. Gamete release occurs in response to cues from individuals of same species = mating or courtship rituals (and sometimes pheromones).
what is internal fertilization? mention types
usually requires an intromittent organ, such as a copulatory organ. These can be fins in fishes (Claspers in sharks, gonopodium in guppies and mollies), limbs in some mollusks and arthropods, and penis in birds, turtles, crocodilians, and mammals. Other structures also are used also. For example, some salamanders and some arthropod groups use spermatophores, which are specialized structures produced by males that bear sperm. Male deposits a spermatophore, which is laden with sperm; a female will pick up the spermatophore.
birth: what is oviparity, viviparity, and ovoviviparity?
oviparity (egg-laying), viviparity (live-birth), and ovoviviparity (egg retention).
organization of the reproductive system in vertebrates: how are jawless fish organized?
do not have ducts to transport their gametes. The gametes are shed from the gonads directly into the body cavity, where they exit the body through pores either in the body wall or cloaca.
organization of the reproductive system in vertebrates: how are jawed organisms/mammals organized? reference drawn figure 2 label
All jawed vertebrates have a series of ducts that the gametes pass through to exit the body. A pattern to the ducts exists. Two pairs of parallel ducts develop. One pair will develop into the male duct system (e.g. vas deferens). The name used to refer to this duct varies, but early on in development it is often referred to as an archinephric duct(mesonephric duct). This is because in vertebrate embryos, these ducts initially transport urine (arch = ancient; nephric = kidney). The other pair of ducts develops into the female ducts (oviducts, uterus, etc.), and in early development, these ducts are often called paramesonephric ducts (para = alongside, meso = middle, nephric = kidney). only one pair of ducts persist.
organization of the reproductive system in vertebrates-jawed mammals: how is the persistence of one pair of ducts chosen in placental mammals?
Sex of an individual placental mammal is determined by genes on a specific chromosome. Of our 23 pairs of chromosomes, we have one pair of sex chromosomes. Male mammals are XY; whereas, female mammals are XX. Conventionally, the default for placental mammals is for an embryo to develop into a female, unless triggered to develop into a male. Gonads develop and enlarge, but do not differentiate into ovaries or testes early on during embryonic development, and both duct systems are also developing, with the archinephric duct transporting urine in early embryos of both sexes. One gene associated with the Y chromosome in a developing male mammal will trigger a change in the developmental pathway. This gene is associated with a region of the chromosome known as the sexual region of the Y (SRY). When activated, this gene will cause the production of a gene product that will cause the indifferent gonads, which by default would develop into ovaries, to develop into testes. When the testes differentiate, different cell types develop within them, including Interstitial cells that will produce testosterone, and sertoli cells that will produce a Paramesonephric Duct Inhibiting Factor (PDIF). Testosterone will cause the archinephric duct to persist, and it develops into the vas deferens, which will eventually transport sperm. The PDIF will cause a regression of the paramesonephric ducts, which linger in males as small ligaments or cords (non-functional).
organization of the reproductive system in vertebrates-jawed mammals: how is the external genitalia developed due to testosterone?
If a mammal is XX (female), then there is no Y chromosome, no SRY, and the indifferent gonads develop into ovaries. In the absence of sufficient quantities of testosterone, the archinephric ducts degenerate, and without Sertoli cells, no PDIF is produced, and the Parmesonephric ducts persist as the oviducts, uteri, etc. Also, the external genitalia develop into the female condition. Note that in any mammal, maleness or femaleness is regulated by chemical coordination, requiring appropriate receptors in cells of many organs.
organization of the reproductive system in vertebrates-other vertebrae: how is sex chromosomes determined in turles of crocodilians and some lizards? and what are the two names its called?
determined by the temperature at which the embryos are incubated. A biologist can gather a hundred eggs from a sea turtle and incubate them at a temperature to produce 100 females, 100 males, or any combination of sexes desired. This type of development is termed Environmental Sex Determination (ESD) in general, or Temperature-Dependent Sex Determination (TDSD) specifically. Some lizards also are known to use TDSD to determine which sex will develop. Many biologist are concerned about how change in climate and habitat might be affecting sex ratios of many species that use ESD to regulate sex of embryos.
organization of the reproductive system in vertebrates-other vertebrae: what/how do some types of toads use to change sex? fish also can change sex but not using this organ
in some toads, a specialized portion of the indifferent gonad persists in males, which is called a Bidder’s organ. Damage to the testes can cause Bidder’s organs to develop into ovaries.
