Animal Chromosomes – Numbers and Reproducing

Since I began to learn about genetics in biology last year, I have become very interested in how they work and the science behind them. Furthermore, this was encouraged by one of my first posts on owl classification when I talked about the differences in tytonidae and strigidae owl families. During the time when I researched that, I began to look into the genetic differences, and although finding none in these two species, I was eager to learn more. In terms of chromosomes, all I know is that humans have 23 pairs in every cell of their body except the gametes (sex cells) which only have one set of 23 meaning that when the sperm and egg fuse a complete set of 46 will be made. I also know that different animals have different numbers of chromosomes, which determines if they can reproduce with one another or not. However, I am interested to know how many chromosome pairs different animals have and the limitations between breeding because of this.

http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count

This wikipedia link lists a cross-section of different animal, plant and protist (eukaryotic (organism whose cells contain complex structures within a membrane) microorganisms) groups. The highest count of diploid ( 2 complete sets of haploid (number of complete chromosomes in a gamete)) is 1440, found in a fern called Adders-tongue.

Whilst the organism with least diploid chromosomes is the Jack Jumper Ant in which the female has 2 and the male is haploid so only has 1!

From the sites I am researching, I feel out of my depth because of the vocabulary being used and need to clear up the different types of ‘ploidy’. Ploidy is the number of sets of chromosomes in an individual cell. The haploid number is referred to as and this is the number of chromosome sets in a gamete. But monoploid is the number of unique chromosomes within a single complete set. A pair of chromosomes is called a homologous pair. As the sets of chromosomes increase so does the name given to them, triploid (three sets), tetraploidy (four sets – common in plants), hexaploid (six sets) etc. Species, such as the Jack Jumper Ant, where one sex is haploid whilst the other is diploid are called haplodiploid. (http://en.wikipedia.org/wiki/Ploidy#Homoploid)

Although I am now overwhelmed with new vocabulary, I am beginning to understand the differences between different species and the number of chromosomes, as well as the number of sets of chromosomes, they have. But what determines these numbers?

But as no one really knows, this is a hard question to ask. However, related species generally have similar chromosome numbers. So how similar do they have to be to able to reproduce?

I decided to look at the example of the mule. In the list of animal chromosome numbers, horses have 64 and donkeys have 62, so a mule has 63. Therefore, the numbers of chromosomes have to be similar, although this does not mean that a dolphin could reproduce with a badger because they both have 44 chromosomes. The other thing that makes a difference is the similarities between the strands of DNA themselves. The genes have to be similar in lengths. A horse and donkey genes are similar enough to fuse, however they are not similar enough for mules to go through meiosis in order to make gametes. In this process, chromosomes have to match up and with different genes this cannot happen so mules cannot reproduce. Read more about mules: http://genetics.thetech.org/ask/ask225

In conclusion, the number of chromosomes, which range from 1 – 1,400, the number of sets and the length of the chromosomes determine the relationships animals can have with one another. However, when genetic mistakes occur, problems can arise. For example Down’s Syndrome is caused in humans by the presence of an extra chromosome number 21.

The Muscular Tongue

The other day, when casually watching my dog lick my hand, I noticed what an amazing piece of anatomy the tongue really is. Having never considered it much before I know little, however, I am already aware that it is a muscle, the only one in the body only attached at one end. Although tongues are quite special, they are limited in flexibility, mainly used for shaping words to enable talking, not to mention tasting. But what I really want to know is how a dogs tongue can be so flexible, able to wrap around almost any object whilst taking its shape. I find this especially puzzling when comparing it to other muscles which move in one direction only and require an antagonistic pair.

In the tongue there are also muscle pairs. These are called extrinsic, on the outside of the tongue attached to other structures, and intrinsic, entirely within the tongue. There are four pairs of each.

 

Extrinsic Muscle names and function:

Genioglossus muscle – protudes the tongue as well as depressing its centre

Hyoglossus muscle – depresses the tongue

Styloglossus muscle – elevates and retracts the tongue

Palatoglossus muscle – depresses the soft palate and elevate the back of the tongue

 

This diagram shows the extrinsic muscles outlined in blue and labelled. It can be seen where they attach to other structures in comparison to the tongue. There are a couple of other muscles labelled as well. These are the stylohyoid and geniohyoid muscles, which although they contribute to the movement of the tongue, they are no attached to it so do not count as tongue muscles. The Mandible and Hyiod bone are structures within the throat whilst the Frenulum attaches the tongue to the base of the mouth. Tongue and tooth are self-explanatory!

 

Intrinsic Muscle names and function:

Superior longitudinal muscle – elevates, retracts or deviates the tip of the tongue.

Inferior longitudinal muscle

Verticalis muscle

Tranversus muscle

These intrinsic muscles are mainly responsible for maintaining the shape of the tongue rather than assisting movement.

 

This diagram is my interpretation of the intrinsic tongue muscles, extremely  simplified. It is based on the information that the superior longitudinal runs along under the surface, the inferior longituninal lines the sides, the verticalis joins the inferior and superior longitudinal muscles in the middle and the traversus divides the tongue at the middle, attached to the sides.

 

After doing this research into the human tongue, I can conclude that a dog, or any vertebrate, would have a very similar tongue. However, my prior assumptions have been proved wrong for many reasons. Firstly, a dog’s tongue only appears so much more flexible than ours because of the long length and thin depth. Also, I previously thought that the tongue was one muscle, therefore I was confused at how it could move as it does, especially as there is no apparent antagonistic pair. But now I know the complexity of the eight muscles, both inside and out, working together to fulfill the movements we need for talking, eating and many other activities our mouths would not be complete without.

From starting this research I began to look specifically into dogs. Although the muscular knowledge was sparse because of the similarity to humans, I found that there was a lot more to find out about a dog’s tongue. This has made me interested so I will expand my research into another post more on The Tongue.

 

References:

http://en.wikipedia.org/wiki/Tongue

http://en.wikipedia.org/wiki/Muscles_of_tongue

http://www.rci.rutgers.edu/~uzwiak/AnatPhys/APFallLect14.html

Kingsnorth Vets – 25th July 2012

On Wednesday, I spent the day once again watching a small selection of operations. The most interesting of which was a Bernese Mountain dog who had melanoma in its tail so had to have it amputated. The vets thought very carefully about where exactly the incision should be made. It had to be significant enough to completely get rid of the cancer however, there was no reason why the whole tail should be removed to leave only a small stump as the melanoma was situated near the end. But they had to think about the wound and the damage it could come to from a very waggy dog! Therefore they decided to amputate two thirds from the end of the tail so one third of the original was left. This meant that the tail would not escape past the hind legs of the dog and so the stump would be unable to hit anything on happy wagging expeditions.

Once the dog was anaesthetised its tail was shaven and thoroughly cleaned with antiseptic whilst I held up the tail. It was bandaged so that only the portion revealed was where the incision would take place. When taken into theatre this had to be covered by the vet with a sterile bandage to ensure that everything was sterile and no infection could be spread during the procedure.

The incision was located at the gap between two vertebrae of the tail.

Tail amputation diagramThe incision itself had to be a very specific shape in the skin. The oval, as shown here, had to be cut symmetrically on both sides to maintain the shape of the tail when it was stitched.

 

Tail blood vesselsOnce the skin had been cut, the three major blood vessels had to be located as shown in this diagram. It was very important that all three were tied off with catgut suture before being cut through to inhibit as much blood loss as possible. Furthermore, the less blood, the easier the operation becomes. As demonstrated by the vet who helping with the procedure who constantly dabbed at the open wound with a swab.

Once this had been done, the amputation itself was ready to take place. A tail is much easier to separate than most other bones going through the same operation. This is

because of the convenient gaps between each piece of bone, or vertebrae. This means that an ordinary scalpel could be used to cut through the cartilage rather than a bone saw.

Once the end of the tail has been removed, the two ovals could be stitched together around the remaining stump of vertebrae. Leaving a perfect, melanoma-free tail!

This amputation was the longest I have observed but there was still time afterwards to see a cat who had bitten its own tongue. It was put under anaesthetic so it could be inspected with ease. The edge of the tongue had blackened with lack of blood and was hanging on only by a measly bit of flesh. The vet suspected that it had been like this for a few days and if had been brought in immediately, the piece of tongue could have been stitched back into place. However, as the area that had encountered the cats teeth had almost completely healed over, the only thing to do was to cut off the bit of tongue and put in place a few stitches where it had not yet healed over.

From seeing these unusual operations, I have observed the importance of precision in veterinary practice in everything you do.

 

Kingsnorth Vets – 23rd July 2012

On Monday, although nervous, I was more certain than previously of what to expect. I knew that I would have to spend a lot of time standing around and not doing much, but I also realised the reasons for this and the inability for there to be anything for me to do as a completely unqualified school girl. However, although there would be waiting to do, my patience would be rewarded.

Luckily I didn’t have to wait long. There was a long list of operations to be done and I could see the importance of careful organisation and planning. There were two cat spays, a cat castrate and a dental. These had to be positioned so that the time available was used most successfully. When considering this there are some factors which come into account. This includes the length due to complexity of the operation, but most importantly, the time the pre-meds and general anaesthetic could be administered. In most animals the pre-meds are given about half and hour before the operation when a general anaesthetic will be given. The pre-medications are sedative drugs used to calm the animal and make it easier for it to be handled whilst being injected with anaesthetic. This means that the nurses must be informed as to the time for the specific animal to have its pre-meds, determined by its weight. When choosing the order of Monday’s operations, the vet chose to do the cat castrate first and the dental last with the spays in the middle.

As a castrate is a relatively simple operation so it is done in the prep room rather than the theatre and is very quick. Unfortunately, the cat which was being operated on, did not stay calm as it should under sedative. After much wriggling and scratching, the attempt was given up to inject a peripheral vein with anaesthetic and gas had to be resorted to. At this point I had to leave the room so that there was no chance of the gas affecting me. Once the cat was unconscious the procedure was carried out as normal. But I learnt that with gas, the anaesthetic is more likely to be unsuccessful and the cat will almost certainly wake up sooner than normal.

The morning continued as I watched two cat spays and the struggles of the young vet to stitch it as neatly as possible. Furthermore, I listened with interest to the vets discussing the advantages and disadvantages of using different suture threads to tie off the ovarian blood vessels. They were arguing out whether catgut or vicryl was easiest and most effective.

Finally on Monday, I watched a dog have a dental, it was explained to me the process of tartar build up. It begins as plaque which is a deposit of bacteria from all the food we eat. Plaque can be very easily removed through brushing, or products such as specially designed dental chews. However, the constant build up of plaque results in tartar. This is damaging, causing gum disease and bad breath. Tartar can be not so easily removed, it has to be chipped off with metal instruments and causes many teeth to rot and therefore have to be removed. The dog I watched had about five teeth removed as I observed the use of a chart naming the teeth so they would have a record of what had been done. The vet explained to me that it was impossible to know until the tartar was chipped away what damage the teeth would be in. Dentals are very hard to predict because of this and the one I watched took longer than I expected it would.

After a busy morning, I could see the need to keep on top of organisation and work, never underestimating what would come up.

Kingsnorth Vets – July 2012

After previously doing work experience in February at Kingsnorth Veterinary Centre, I knew that I wanted to do more. This way I wanted to increase my experience and knowledge which grows from this. The contact I already have is good and I am friendly with many of the receptionists as well as nurses who I often see on a daily basis when walking our dogs! With the further involvement with often taking my own animals to the vets, it was easy to ask if I could organise my own work experience rather than relying on school. So I arranged for the first week of my holidays doing mornings at Kingsnorth Vets once again.

From the 23rd to the 27th July, I spent from 8.30 until about 1.00 observing a variety of consultations and operations as well as helping out around the kennels. Some days, more happened than others. These were Monday and Wednesday when I was observing operations. Therefore I will go into them further on my next posts. Tuesday, Thursday and Friday I was watching consults. They were similar to those which I watched in February. Many featuring booster vaccinations, animals feeling down or being put down. Some were submitted into the kennels to checked over more thoroughly, put on an intravenous drip or having xrays. A few cases which stand out from the rest include an adorable pomeranian puppy which came for its first vaccination on Friday. It squealed as soon as the needle pierced its skin, despite our best efforts to distract it! Another special moment would be the cocker spaniel which was being put on an intravenous drip. The vet handed it over to me as he organised himself and then showed me how to hold the foreleg in order to create traction causing the vein to protrude. This was great to be able to help and experience a simple yet important process first hand, as well as cuddling a very lovely dog!