Hello Gowtham,
The truth is we don’t know the exact number of genes in fish, but there are estimates. We’ll tell you a little about what is known about fish genomes and why estimating gene numbers can be a tricky business.

The genomes (the complete sets of DNA) from several types of fish have been sequenced. These fish include zebrafish, fugu (Japanese pufferfish), Tetraodon (green spotted puffer), medaka, and the three-spined stickleback. One of the reasons that the two pufferfish were chosen for DNA sequencing is because their genomes are relatively small. The tetraodon genome is built of a mere 340 million base pairs of DNA. The human genome is nearly 10 times that size at 3 billion base pairs! In contrast, the zebrafish genome is comprised of 1.5 billion base pairs, which makes it is closer to the size of the human genome. Despite the big differences in the sizes of their genomes, fish and humans are believed to have similar numbers of genes. It is currently estimated that the human genome harbors around 20,000–25,000 genes.

With the complete genome sequences for so many types of fish in hand, how come we don’t know exactly how many genes they contain? In addition to genes, genomes contain structural elements like centromeres and telomeres, as well as “junk DNA” for which a clear purpose has not yet been uncovered. Before researchers had determined the complete genome sequences for so many organisms, they identified genes by studying the behavior (phenotypes) associated with mutations in specific genes or by studying isolated (cloned) DNA from different organisms. These are still important techniques, but the availability of entire genome sequences has allowed scientists to estimate the location of genes much faster. There are certain molecular signals and signposts that scientists look for in DNA sequences that indicate the presence of a gene. For example, protein-coding genes begin with ATG, which encodes methionine, and end with a stop codon (UAA, UAG, or UGA). Long stretches of DNA sequence that do not contain stop codons are candidate sequences for genes.

There are several features of genes that can make their identification tricky. Introns (noncoding sections of genes that later get removed from RNA transcripts) can be difficult to identify. Also, although distinct sequences are found in protein-coding genes, not all genes encode proteins. Instead, many genes encode functional RNAs. Another difficulty is the presence of pseudogenes, which are relatives of functional genes that are no longer in use. Computer programs have been developed that use all the DNA sequence information from a given genome to predict the sizes and locations of its genes. And these programs have been very useful in providing us with gene estimates. However, laboratory testing is required to tell for sure which sequences correspond to active genes. As you can see, much work remains to be done before we have a complete tally of the number of fish genes. Nonetheless, an amazing amount of progress and many fascinating and unexpected discoveries have already been made!

If you would like to learn more about fish genomes and estimates of gene numbers, check out the following links:

http://learn.genetics.utah.edu/content/begin/dna/

http://www.nature.com/scitable/topicpage/pufferfish-and-ancestral-genomes-29154

http://www.sanger.ac.uk/modelorgs/zebrafish.shtml

http://uswest.ensembl.org/Danio_rerio/Info/Index

http://www.fugu-sg.org/

http://www.genoscope.cns.fr/externe/tetranew/

http://www.genoscope.cns.fr/spip/Tetraodon-nigroviridis-a-fish-with.html

http://utgenome.org/medaka/

http://www.broadinstitute.org/models/stickleback

http://uswest.ensembl.org/Gasterosteus_aculeatus/Info/Index

http://www.genome.gov/25020001

Hello Nakkala,
Following transcription, the resulting mRNA molecules undergo splicing in the nucleus. To answer your questions, let’s first start by discussing mRNA splicing, then we’ll address the specific details of your question. To begin, mRNA splicing is an essential and highly regulated eukaryotic process carried out by spliceosomes. Spliceosomes consist of both RNA and proteins, and they rival the ribosome in their size and complexity. When an mRNA (called a pre-mRNA) is first made, it comprises two different types of segments: exons and introns. In a nutshell, exons combine to encode a protein and introns are intervening non-coding segments. Splicing removes the intervening non-coding introns from the pre-mRNA, allowing the exons to be linked together to produce a mature mRNA. The resulting mature mRNA then serves as a template for the translation of its encoded protein once it arrives in the cytoplasm.

You’re certainly correct in stating that introns are nucleotide sequences, just like exons. The reason that introns are not used to produce a functional protein is that introns do not code for protein sequences. You must be wondering why introns exist if they don’t even code for proteins! One reason is that some introns carry instructions for how the mRNA should be handled by the cell. A second reason introns exist is that they allow a single gene to be spliced into a variety of different forms. This process, called alternative splicing, lets one pre-mRNA molecule be edited to form slightly different mature mRNAs, which can go on to act as templates for the production of different proteins. As you might guess, this ability to make slightly different (and sometimes very different!) proteins from the same pre-mRNA could provide evolutionary advantages to an organism.

To learn more about introns and splicing, check out the following helpful Scitable articles:

http://www.nature.com/scitable/definition/intron-introns-67

http://www.nature.com/scitable/topicpage/the-information-in-dna-is-decoded-by-6524808

http://www.nature.com/scitable/topicpage/rna-splicing-introns-exons-and-spliceosome-12375

http://www.nature.com/scitable/topicpage/chemical-structure-of-rna-348

http://www.nature.com/scitable/topicpage/rna-functions-352

Hello Gowtham,
Biotechnology is the application of biological processes and organisms to produce commercial goods. One of the oldest examples of biotechnology is the use of yeast to produce bread. Today, biotechnology is used in bioengineering, medicine, agriculture, and many other fields. Scientists can manipulate genes using molecular biological approaches to produce organisms with desirable properties that did not previously exist in nature. For example, genetically engineered bacteria can be used to produce drugs and synthetic hormones, such as insulin. Additionally, biotechnology has been used to produce biofuels and genetically modified foods that are resistant to diseases, insects, and frost.

As you might guess, there are many other applications of biotechnology! We’ve provided a list of resources below to help you learn more about this fascinating and ever-expanding field. Enjoy!

Scitable has created a Spotlight on Genetically Modified Organisms that provides myriad resources about biotechnology in plants and animals:

http://www.nature.com/scitable/spotlight/GMOs-6978241

For a list of biotechnology journals and some of their featured hot-off-the-press biotechnology articles, check out this link:

http://www.nature.com/biotech/index.html

For basic information about the definition of biotechnology and a timeline of historical events in biotechnology (starting in 1750 BC), follow these links:

http://www.nature.com/scitable/definition/biotechnology-151

http://www.biotechinstitute.org/what_is/

http://www.biotechinstitute.org/what_is/timeline.html

To learn more about the methods used in biotechnology, check out these links:

http://www.nature.com/scitable/topicpage/Recombinant-DNA-Technology-and-Transgenic-Animals-34513

http://www.nature.com/scitable/topicpage/The-Biotechnology-Revolution-PCR-and-the-Use-553

To learn more about health-related biotechnology, see these links:

http://www.nature.com/scitable/topicpage/Gene-Based-Therapeutic-Approaches-3881

http://learn.genetics.utah.edu/content/tech/genetherapy/

http://learn.genetics.utah.edu/content/health/pharma/

http://learn.genetics.utah.edu/content/tech/cloning/index.html

To learn more about plant and environmental biotechnology, follow these links:

http://www.nature.com/scitable/topicpage/Genetically-Modified-Organisms-GMOs-Transgenic-Crops-and-732

http://www.nature.com/scitable/topicpage/Quantitative-Genetics-Growing-Transgenic-Tomatoes-1123

http://www.nature.com/scitable/content/Plant-genetic-engineering-for-biofuel-production-towards-45102

http://www.nature.com/scitable/content/Genetic-modification-The-production-of-recombinant-pharmaceutical-15030

To learn more about current issues and innovations in the biotechnology field, check out this link:

http://www.bio.org/

Hello Gildardo,
Pregnant women aren’t just eating for one — they’re eating for two (and sometimes even more than two!). When it comes to prenatal nutrition, not all foods are created equal: some types of food and nutrients are recommended for pregnant women while others should be avoided.

Of course, a balanced diet rich in grains, fruits, vegetables, protein (meats and beans), and dairy is highly recommended for all pregnant women. However, diet alone cannot provide all the key nutrients required for a healthy pregnancy, and pregnant women should also take a daily prenatal multivitamin. So, what are some of the best prenatal nutrients? Prenatal multivitamins are especially rich in folic acid, calcium, and iron. Other vitamins important for a healthy pregnancy include vitamins A, C, B6, and B12. Some pregnant women also take omega-3 and vitamin D supplements (or drink more vitamin D-containing milk).

What foods should pregnant women avoid? As you likely know, pregnant women should avoid alcohol (e.g., beer, wine, mixed drinks), smoking, and illegal drugs. It is also recommended that pregnant women avoid caffeine or limit their intake. They should also avoid fish (e.g., shark, swordfish, king mackerel, tilefish, albacore tuna) and shellfish that contain high levels of mercury. Pregnant women also should not eat unpasteurized juices, milk, and soft cheeses. Finally, they should avoid undercooked meat, poultry, and shellfish, as well as prepared meats (e.g., deli meats, hot dogs — unless they are reheated before eating).

As you can see, it’s not necessarily diet-as-usual once a woman becomes pregnant. Inevitably, women adjust their food and vitamin intake to help facilitate a healthy pregnancy.

For general information about pregnancy and nutrition-associated birth defects, follow these links:

http://www.nature.com/scitable/topicpage/birth-defects-prevention-and-treatment-859

http://www.nature.com/scitable/topicpage/birth-defects-causes-and-statistics-863

http://www.nlm.nih.gov/medlineplus/pregnancy.html#cat10

http://www.nichd.nih.gov/health/topics/pregnancy.cfm

http://www.acog.org/publications/patient_education/ab005.cfm

http://kidshealth.org/parent/pregnancy_newborn/pregnancy/preg_health.html

Check out these links to learn about recommended foods and nutrition during pregnancy:

http://www.mayoclinic.com/health/pregnancy-nutrition/pr00110

http://www.acog.org/publications/patient_education/bp001.cfm

http://win.niddk.nih.gov/publications/two.htm

To learn more about prenatal vitamins, see these links:

http://www.mayoclinic.com/health/prenatal-vitamins/PR00160

http://www.marchofdimes.com/pnhec/173_15354.asp

To learn more about foods to avoid during pregnancy, follow these links:

http://www.mayoclinic.com/health/pregnancy-nutrition/pr00109

http://www.marchofdimes.com/professionals/14332_1152.asp

http://www.epa.gov/waterscience/fish/advice/