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Transcript of Sexual Reproduction
Reproduction One parent provides all of the offspring's genes; there is no fusion of sperm and egg Two haploid gametes fuse to form a zygote fission (seperation of a parent into two or more individuals of approximately equal size) How? (new individuals arise from outgrowths of existing ones) budding hydra fragmentation and regeneration in planaria sea anenome undergoing fission Pros? only requires one parent (esp. useful for individuals that rarely encounter others of the same species, e.g. parasites)
produces more offspring Many animals are either one or the other, but some animals may alternate between asexual and sexual reproduction. This is possible through methods such as: an egg develops without being fertilized; as haploid adults, they will produce eggs without meiosis parthogenesis hermaphroditism each individual has both male and female reproducive systems; one could fertilize onself, but mating with another individual will produce two fertilized sets of eggs sequential
hermaphroditism an individual changes its sex during its lifetime Pros? doesn't produce identical copies = genetic variablity = greater chance of survival when environmental factors change
few offspring = each can recieve more parental care during its lifetime Vivien Ngo, period 0 asexual budding (breaking of body into several pieces) +
(regrowth of lost body parts) fragmentation
+ regeneration sexual in Humans Males Females Oogenesis Spermatogenesis Gametogenesis in Humans produce ova (egg cells, the female gametes) in the ovaries produce sperm, the male gametes, in the seminferous tubules of the testis production of gametes (bases on meiosis) usually occurs in gonads (e.g. ovaries in females, testes in males) There are two modes An oocyte matures roughly about once per month (once per each reproductive cycle). ovary specific stem cell that undergoes meiosis to give rise to prmary oocytes arrested in prophase I; it is thought that all are present at birth FSH stimulates follicle and causes the prmary oocyte to complete meiosis I and start meiosis II occurs when the follicle
is ruptured arrested at metaphase II until entry of a sperm degenerates if egg is not fertilized *please zoom in and navigate the diagram yourself *please zoom in and navigate the diagram yourself stem cell that
undergoes meiosis to give rise to sperm Structure of a Sperm Cell acrosome has enzymes to help penetrate the egg
tail (flagellum) helps sperm swim to egg
mitochondria provide ATP to move tail Males can
throughout their whole lifetime. Mechanisms of Fertilization (the fusion of to gametes to form a zygote) The main goal is to help sperm meet eggs of the same species External
Fertilization The female releases eggs into a wet environment (so gametes won't dry out), where released sperm can swim to them. Timing is important, so that mature sperm meet ripe eggs. How do they know when it is the right time? Environmental cues (temperature, day length)
Chemical signals (phermones)
"Courtship" behavior Internal
Fertilization Sperm are deposited in or near the female reproductive tract. where fertilization occurs; adaptation that allows terrestrial animals to transport sperm to eggs, even though the environment is dry Before gametes are delivered, they must be produced in the reproductive systems. *click the videos to play The Reproductive Cycle in Females consists of two parts:
Uterine (menstrual) cycle, which consists of changes in the uterine as shown in figure e.
Ovarian cycle, which consists of the changes in the ovaries, as illustrated by figure c.
Changes in the uterus are a result of preparation of the developing eggs from the ovarian cycle; thus, both make up the female reproductive cycle.
It is dictated by the levels of the hormones:
FSH (follicle stimulating hormone), figure b
LH (luteinizing hormone), figure b
estrogen, figure d
protogesterone, figure d
*please zoom in and navigate the diagram yourself Reproductive Anatomy The simplest systems produce gametes from undifferentiated cells lining the coelem, which eventually fills up with gametes until released by a method that depends on the species.
The most complex have differentiated male and female gonads accompanied by accessory tubes and glands that carry, nourish, and protect gametes or embryos. varies from species to species have seperate sexes. Female eggs are developed in the ovaries; then they are sent to the vagina, where fertilization occurs. Males ejaculate sperm into the female reproductive system. In many species of insects, females can store sperm in a sac called the spermatheca*. Insects Reproductive system of a queen bee Vertebrate have very similar reproductive systems, but there are some prominent differences:
The digestive, excretory, and reproductive systems of many nonmammalian vertebrates all open at a common opening called the cloaca.
In most vertebrates, the uterus is divided into two chambers, but in humans and a few others, the uterus is not divided at all.
Many nonmammalian vertebrates do not have a well-developed penis and instead turn the cloaca inside out to ejaculate.