Biomes are typically divided based on yearly temperatures and precipitation amounts. Deserts have high temperatures with very low precipitation. Rainforests have high amounts of precipitation with high temperatures. Tundras have very low temperatures with little to no precipitation.

Until 2006 Pluto was classified as the ninth planet. At that time, it was declassified as a planet and reclassified as a "dwarf planet."

Neptune is the eighth planet in our solar system. Titan and Ganymede are moods of Saturn and Jupiter, respectively.

The universe was thought to begin because of the Big Bang, which occurred around 14 billion years ago.

The air in the atmosphere is largely composed of nitrogen and oxygen. Nitrogen represents the largest contributor, composing approximately 79% of the earth's atmosphere. Oxygen represents about 20% of the earth's atmosphere. Other gases, such as hydrogen, carbon dioxide, and methane, comprise less than 1% of the atmosphere.

Helium is frequently used in balloons at parties. It is lighter in mass than the surrounding air, allowing it to "float" upwards. As a noble gas, helium is also largely inert and has numerous practical purposes in chemistry due to this property.

从2013年开始,氦的用量to far exceed the supply, resulting in a helium shortage.

氖和氩惰性气体(如氦)。水ogen is not a noble gas, and is actually highly reactive.

Because RNA is usually single-stranded (vs. double-stranded DNA), it is more susceptible to degradation by nucleases; therefore, RNA is NOT more stable than DNA.

RNA does contain the carbohydrate sugar ribose in its backbone, while DNA contains the sugar deoxyribose. RNA contains the nitrogenous base uracil; in contrast, DNA contains thymine.

Transcription is initiated when RNA polymerase attaches to DNA at the promoter site. This allows the RNA polymerase to be appropriately positioned so that the whole gene is transcribed.

The origin of replication is the site that allows the initiation of DNA replication. Operators are segments of DNA that can bind transcription factors and regulate certain genes.

When a gene is sex-linked, it means that the gene is located on one of the sex chromosomes. These chromosomes are the X and Y chromosomes, with the Y chromosome only being found in males. Sex-linked genes provide the opportunity for the frequency of a phenotype to be seen more often in one gender than the other.

Sex-linked genes can be represented in either sex; if the trait is on the X chromosome, it can be displayed in both males and females but may appear more frequently in males.

a heterozygous organism will have one copy of the dominant allele and one copy of the recessive allele for a given gene. The recessive phenotype is the expression of the recessive allele; this will only occur if the offspring as two copies of the recessive allele.

Since two heterozygotes are mating, each one has a 50% chance of contributing their recessive allele to the offspring. Keeping that in mind, the probability of this happening just becomes 50% multiplied by 50%. This gives us a 25% chance that the offspring will display the recessive phenotype.

In other terms, we can look at all the possible combinations for the offspring. Assume thatArepresents the dominant allele andarepresents the recessive allele.

Each parent will have the genotypeAa. The cross will beAaxAa. The possible resulting offspring will beAA,Aa,aA, andaa. Onlyaawill show the recessive phenotype; therefore, there is a one-fourth chance (25%) that the offspring will show the recessive phenotype.

There are only 23 chromosome pairs in human beings, but there are thousands of genes. This means that many genes will be found on the same chromosome. When two genes are found on the same chromosome, they are said to be linked. Genes that are very close to each other on the chromosome are more likely to travel with each other to the same haploid cell during meiosis, and are frequently inherited together.

An example of linked genes are blue eyes and blond hair. These traits are frequently inherited together because they are found in the same region on the same chromosome.