fertilization

Examples of fertilization in the following topics:

• External and Internal Fertilization

  • After the sperm reaches the egg, fertilization can then take place.
  • External fertilization in an aquatic environment protects the eggs from drying out.
  • Internal fertilization has the advantage of protecting the fertilized egg from dehydration on land.
  • Internal fertilization also enhances the fertilization of eggs by a specific male.
  • The anemone fish utilizes a form of external fertilization.

• Fertilization

  • Fertilization occurs when a sperm and an egg have fused together to form a zygote, which begins to divide as it moves towards the uterus.
  • In medicine, this process is referred to as fertilization; in lay terms, it is more commonly known as conception.
  • After the point of fertilization the fused product of the female and male gamete is referred to as a zygote or fertilized egg.
  • The process of fertilization occurs in several steps and the interruption of any of them can lead to failure.
  • At the beginning of the process, the sperm undergoes a series of changes, as freshly ejaculated sperm is unable or poorly able to fertilize.

• Fertility

  • There are a number of different approaches to measuring fertility rate—such as crude birth rate (CBR), general fertility rate (GFR), child-woman ratio (CWR), total fertility rate (TFR), gross reproduction rate (GRR), and net reproduction rate (NRR).
  • The TFR (or TPFR—total period fertility rate) is a better index of fertility than the crude birth rate because it is independent of the age structure of the population, but it is a poorer estimate of actual completed family size than the total cohort fertility rate.
  • Demographers study the factors that affect fertility in order to better understand fertility patterns and their variance.
  • Fertility has been found to correlate to human development index, with more developed countries having lower fertility rates than less developed ones.
  • Examine the impact of fertility rates on society and the various ways fertility is computed and discussed

• Double Fertilization in Plants

  • Angiosperms undergo two fertilization events where a zygote and endosperm are both formed.
  • Together, these two fertilization events in angiosperms are known as double fertilization .
  • After fertilization is complete, no other sperm can enter.
  • After fertilization, embryonic development begins.
  • This is called a double fertilization.

• Fertilization

  • In fertilization, the sperm binds to the egg, allowing their membranes to fuse and the sperm to transfer its nucleus into the egg.
  • Fertilization is the process in which gametes (an egg and sperm) fuse to form a zygote.
  • The egg and sperm are haploid, which means they each contain one set of chromosomes; upon fertilization, they will combine their genetic material to form a zygote that is diploid, having two sets of chromosomes.
  • To ensure that no more than one sperm fertilizes the egg, once the acrosomal reactions take place at one location of the egg membrane, the egg releases proteins in other locations to prevent other sperm from fusing with the egg.
  • (a) Fertilization is the process in which sperm and egg fuse to form a zygote.

• Life Cycle of a Conifer

  • Conifers are monoecious plants that produce both male and female cones, each making the necessary gametes used for fertilization.
  • At fertilization, one of the sperm cells will finally unite its haploid nucleus with the haploid nucleus of an egg cell.
  • Upon fertilization, the diploid egg will give rise to the embryo, which is enclosed in a seed coat of tissue from the parent plant.
  • Fertilization and seed development is a long process in pine trees: it may take up to two years after pollination.
  • Pollen from male cones moves up into upper branches where it fertilizes female cones.

• Infertility

  • Other factors that affect fertility include toxins (such as cadmium), tobacco smoking, marijuana use, gonadal injuries, and aging.
  • Eggs are obtained from the woman after extensive hormonal treatments that prepare mature eggs for fertilization and prepare the uterus for implantation of the fertilized egg.
  • If fertilization is not accomplished by simple IVF, a procedure known as intracytoplasmic sperm injection (ICSI) can be used to inject the sperm into an egg .
  • IVF procedures produce a surplus of fertilized eggs and embryos that can be frozen and stored for future use; the procedures can also result in multiple births.
  • A sperm is inserted into an egg for fertilization during intracytoplasmic sperm injection (ICSI).

• Data and Methods

  • total fertility rate: the number of live births per woman completing her reproductive life if her childbearing at each age reflected current age-specific fertility rates
  • Another important demographic concept relating to fertility is replacement level.
  • Sub-replacement fertility is a fertility rate that is not high enough to replace an existing population.
  • Fertility rates are just starting to decline in Africa.
  • The chart below highlights the varied fertility rates of specific countries as some have very low fertility rates, many have moderate rates, and some have very high rates.

• Infertility

  • Possible problems could be that the egg is not released at the optimum time for fertilization, that it may not enter the fallopian tube, sperm may not be able to reach the egg, fertilization may fail to occur, transport of the zygote may be disturbed, or implantation fails.
  • Also, polymorphisms in folate pathway genes could be one reason for fertility complications in some women with unexplained infertility.
  • Medical treatment of infertility generally involves the use of fertility medication, medical device, surgery, or a combination of the following.
  • In these methods, fertilization occurs inside the body.
  • Fertilization takes place outside the body, and the fertilized egg is reinserted into the woman's reproductive tract, in a procedure called embryo transfer.

• Implications of Different Rates of Growth

  • Fertility rates refer to the rates of birth per 1,000 women of reproductive age in a given population.
  • However, when the fertility rate deviates from the replacement level, the size of the population will change.
  • Fertility rates above the replacement level will cause the population to grow; fertility rates below the replacement level will cause the population to shrink.
  • Meanwhile, about half the world lives in nations with sub-replacement fertility.
  • Russia and Eastern Europe are dramatically below replacement fertility.