Flu vaccines need to be revised and changed every year because the flu virus constantly mutates. Flu viruses can change in two ways: drift or shift. Antigenic drift occurs when genes of the virus slowly change during replication until the immune system no longer recognizes it. On the other hand, antigenic shift occurs when a major change in the virus happens. This usually leads to a totally different kind of virus. This is what happened during the H1N1 scare in 2009.
DNA viruses like mumps are less prone to mutation due to the presence of DNA polymerase. RNA viruses are more prone to mutation because they undergo reverse transcription to simulate the role of DNA.
Nearsightedness is the answer.
The fertilized egg enters a 2-week period of cell division. during this period, the fertilized egg is known as an embryo.
Following sexual intercourse, sperms move from the vagina via the cervix and uterus to the fallopian tubes, where only a single sperm fuses with the egg.
The fertilized egg or the zygote divides constantly as it travels down the fallopian tube to the uterus. Initially, the zygote is transformed into a solid ball of cells after which it changes into a hollow ball of cells i.e. a blastocyst.
The blastocyst gets embedded in the wall of the uterus, where it evolves into an embryo connected to a placenta and enclosed by fluid-filled membranes.
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The main arctic animals which will be affected by climate change are polar bears, seal, seabirds, and walrus.
Polar bears: Sea-ice cover at summer may be completely loss and this inhibits polar bears traveling from region to another to give birth — making the survival of mothers and cubs to be vulnerable.
Seal: Seal species are living mainly on ice and with the climate changing, ice cover also reduces — creating a not so comfortable environment for seal. They use sea ice as a feeding ground, birth place and a place where for raising their young, as well as for resting.
Seabirds (auks and gulls): They eat fishes and scavenge on top of sea ice, so when sea ice reduces so as their source of food and population.
Walrus: Uses sea ice as a feeding ground and source of food is on the sea floor while using sea ice as a diving platform. So any loss of sea ice cover, also affects their way of feeding and eventually, their population.
Overall, melting of ice affects salinity and temperature of surface waters, thereby affecting other marine life.
Answer:
The follicular phase
Explanation:
In the follicular phase the level of estrogen hormone increases and the egg prepares itself for release. This phase occur between the first day of period and the ovulation. When the primary follicle matures and form secondary follicle, second meiotic division starts and lead to the formation of Graafian follicle which contains a secondary oocytes. Seconday oocytes consists of a diploid DNA and is not released until the second division is not complete.
