Chromosomes How many chromosomes does a normal human being have?

Chromosomes, DNA and genes
Chromosomes are thread-like structures found in the nucleus of all cells (except red blood cells), which contain our genetic meterial (DNA). Chromosomes come in pairs, and a normal human cell contains 46 chromosomes, 22 pairs of autosomes and one pair of sex chromosomes.


Courtesy: National Human Genome Research Institute. Click the link for a very good glossary
on everything gene related.

DNA, or deoxyribonucleic acid, is the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms. A DNA nucleotide is made of a molecule of sugar, a molecule of phosphoric acid, and a molecule called a base. The bases are the 'letters' that spell out the genetic code. In DNA, the code letters are A, T, G, and C, which stand for the chemicals adenine, thymine, guanine, and cytosine, respectively. In base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine.

Genes are pieces of DNA. Most genes contain the information for making a specific protein.

Sex chromosomes. Boy or Girl?
When a spermcel and an egg melt, one chromosome of each pair will be given to the new human being. Chromosome pair 23 will do the same. Females have XX, males have XY (Like in the picture at the right). If the man donates the X part of this pair it will be a girl, otherwise it will be a boy.

Our genetic information, sometimes described as the 'Book of Life', can be envisaged as a compendium comprising two volumes. It is important to remember however that our environment also plays a major role in how we develop and how our bodies work. Read more at genetics.com.au

Trisomy
Most people have 46 chromosomes, in 23 pairs, but some have an extra copy of one chromosome, called a trisomy because there are three of one chromosome pair. This extra chromosome can lead to a variety of abnormalities. The most common trisomy is called Down syndrome, a trisomy of chromosome pair 21. Read more about trisomy



Comments: Chromosomes

Comments 1 to 24 of about 28.
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foxie-mommie - 2 days ago.
I recieved the results back today from the chomosone tests and there were no chromosone abnormalities. I dont know which is harder, knowing exactly what went wrong or not knowing at all. What I've been left with is the reasoning that my babies heart just stopped beating. No known cause but that 'sometimes things like this JUST HAPPEN.' The nurse read the results to me over the phone....'no fetal parts recognizable.' from the D&C. How can they tell me that my baby wasnt recognizable? I understand how the D&C works but those words just seam so harsh and were hard to hear. Today I saw an infant baby girl and I couldnt take my eyes off her. Then I found myself tearing up as I was at the dentist office with my 5 year old son. At McDonalds I saw a pregnant woman and again the tears began to fall. Everywhere I look there is a constant reminder of the loss I have had to endure. People who saw me weeks ago with a little belly now look at me and wonder. I know in time this will get easier but it's something that will never be forgotten. I look at my ultrasound pictures daily as a reminder not to take anything for granted.

number5forme - 4 days ago.
Hello mommy-for-first-time , I truly feel for you (and I am crying ) as I read your messages - I just had a look in the 'chromosone' section to see if there were new postings. I am sorry that I did not read it sooner . I was thinking that I may have been able to help you in some small way get through your grief - and I have just realised that you gave birth BEFORE I did. Maybe you have not kept your page due to the pain you can feel after losing a child? - it is hard to be around 'pregnant' others, I know.... If you are still around, maybe you would like to chat? I have drawn strength from lots of people on this forum and it has helped a great deal to talk to others who KNOW what you have been through. Here if you need me...

mommy-for-first-time - 17 days ago.
Hello all, My heart goes out to all the parents who had to face chromosomal abnormalities in their little babies and more to those who chose to say early goodbye. I was 20 weeks pregnant when i discovered something was wrong with my little baby boy. Ultrasound showed very specific problems in him like thick skin on neck, fluid in chest cavity, strawberry shaped head, absent nasal bone, straight umbilical chord, missing ulna bone in his hand and missing digits in his right hand. His heart was proper. Doctors said that this is typical Trisomy 18 case. We went for Amniocentesis but surprisingly the results came out normal. He had 46 XY chromosomes. I remember his AFP results were normal too. But because of Amniocentesis i started leaking fluid . so fearing an infection of uterus and depreciating health my baby, we decided to say early goodbye. My heart still aches as i miss my baby but more so because i don't know the reason that caused him so much pain. My doctors have no idea what could have caused all the malformation in my baby. This was my first pregnancy. If anyone had any similar incident with them or their close ones please write to me. I am still searching for an answer. Have a brave heart and faith. Our little angels will be back in our lives!

number5forme - 27 days ago.
I have read many posts both here and on other websites and each story has helped me a little whether they were happy endings and shining a positive light on a chromosome problem or if they were sad and had a 'negative' as such end. I am writing this (which is very difficult for me) in the hope that maybe I can be of some help to someone else who may be finding themselves in a bad situation. After my routine U/S at 12 weeks it was discovered that my baby had a 9mm nuchal translucancy - 3 times the max range that they like to see. My husband and I returned home to read up on this and found NO positive stories to hang our hopes on. We were devastated to say the least. I wanted to get an absolute expert opinion (I was in denial) and so went to a women's only hospital where they only did U/S on pregnant women. They suggested a CVS. Now before I go on I would like you to know my LIFELONG beliefs - these are not religious beliefs but deep felt moral/core beliefs that I have held for as long as I can remember. They are 1. I would NEVER terminate a preganancy 2. I would not risk a potentially healthy pregnancy with a CVS or amnio 3. I would keep and love a child no matter what their disability 4. I would not find out the sex of my baby before it was born. This brings me back to my current situation. I say that it doesnt matter what the results are as I wont terminate but my husband is desperate for DEFINITIVE answers (and eventually I am too). so I relent to the CVS after assurances from the doctor that he was VERY experienced and never lost a healthy baby to miscarraige. (So there goes my number 2.) CVS results come back (we got the 2 day turn around) and it is positive for Down Syndrome. Re-devastation. I am still in denial and ask for another U/S in 2 weeks, hoping that the initial CVS is wrong and we will have a clearer picture with baby. 2 week result is confirmed and discover on U/S severe heart defect. My husband wants to terminate. We decide we want to know the sex of the baby. I thought that knowing the sex would help in my decision - if a girl , we already have a girl (Plus FIVE other children from previous marraiges) then as sad as it seems, it may influence me??? You may ask why? A DS boy would not be compared to (as much) by us or anyone else for that matter to my wonderfully perfect and cheeky 2 yr old little girl. (There goes number 4.) I have anguished over this decision for the last 6 weeks. I have researched as much information as I possibly could from DS sites, abortion procedures, heart defects and possible treatments to genetics, forums with people who have already experienced such tormenting decisions. The end result is that I (and IT IS ME as the end decision definately rests with me given that this baby is inside MY body) have decided that I cannot just take my core beliefs into account here. I have to think of my husband and our relationship (2nd marraiges are not easy), my other 6 children and the impact it will have on our already chaotic life. How will it affect us and them individually??? And not the least how it will affect THIS child - will the daughter I carry inside me have a terrible existence with potentially severe mental retardation and major health problems? Spending many days and or weeks in hospital? Will her life end early? Only to have known pain and suffering? There is no way of knowing how mild OR SEVERE. It is the unknown which I have found the hardest to come to terms with. Nonetheless I have made my decision. Taking everything into account , I have decided to terminate. (There goes number 1.) I will be induced early this coming week to deliver my child who of course is certain to die either inutero or soon after birth. It is not an easy decision to come to and either way I know there will be guilt and regret. It is the best of two very bad situations FOR US. I know I love this baby with all my heart for that ther eis no doubt and she was certainly a planned and very wanted child but sadly I have still come to the decision to end her life. (number 3. out the window) I am now deciding on funeral arrangements instead of nursery colours. Very sad. It shows you that until YOU are in the exact same position, when it comes down to it you dont REALLY know what YOU will do until YOU are faced with these tormenting decisions YOURSELF. Keep an open mind when you judge people for the decisions they make. I empathise with all of you who are in that decision making position right now. Know that (eventually) what is right for YOU will come to you, just give yourself some time. Hugs to ALL of you.

babeemama - 37 days ago.
I got the call today from genetics and all is normal Praise GOD. It takes a special person to raise and love babies with a disablity I know the Lord would have gotten me through but honestly I sighed a breath of relief....

misz-cashis-oct08 - 37 days ago.
well unfortunately i got the results of my CVS today.the baby has down syndrome. and i am devastated. like ive alreddy had 2 miscarriages and now i thought i was finally having a healthy pregnancy.i go on friday to talk to the genetic counselor and discuss my options which is basically to keep the baby with down syndrome or abort my pregnancy.i dont want to abort but i dont know wat else to do. =/ hope u girls are doing better than me <3

happymema - 39 days ago.
babeemama..my daughter had an elevated afp and after waiting 3 wks for level 2 u.s. at 19 wks we found that she is carrying a little boy and little girl but the little boy has gastroschisis, an opening in the abdomen. They both also had a fluid filled cyst and he offered her the amnio but he stated that their hands and feet looked normal and when we asked him what he would do he stated that he didnt feel it was necessary. I wish your doctor had explained a little more to you but the geneticist should be able to give you more info. Good luck to you!

babeemama - 50 days ago.
I had my 20 wk us done tuesday and yesterday was called saying the baby had a spot on his heart and a cyst on his head they recommend i see a genetics dr and have ammino done tommorrow. I was told this had an increase in carrying a baby with down syndrome, has anyone else had these findings?

misz-cashis-oct08 - 51 days ago.
i am so0 upset. and i need advice. i got my ultrasound today for the neuchal translucency testing. well they sed anything over 3 they reccomend a CVS. mine was 3.2 and i am so upset and scared. i want to get the CVS because i think thats he right thing to do for me. is .2 alot over?! im relle worred. could the CVS testing turn up normal or is something definately wrong?! im sooooo stressed and terrified. i dont want anything to be wrong. i feel horrible. =[

suezq - 70 days ago.
This is my third pregnancy in 1 1/2 years. The first ended in Trisomy 18 where our nuchal was perfect but our Amnio came out questionable. Final results gave the boy child very little hope and if survived would be dead in the first year. Trisomy 18's can be deaf, blind, are severly mentally retarded, have every organ affected, can't eat or cry or stretch their limbs out. We terminated the pregnancy. We wouldn't have let an animal live that way much less a child. Our second pregnancy showed a very bad nuchal with fluid gathered at the back of the skull that was the size of the head. A CVS test came back with Turner's syndrome which is a sex chromosome thing. The babies are always girls. They will be short, mentally challenged sometimes, won't develope properly into women without hormone therapy , sometimes don't get periods, and never can have their own children. We terminated because the doctors said the large amount of fluid would eventually drain into the body cavity and drown the baby and it will die. Now I'm 8 weeks pregnant with our last try and I'm going strait for the CVS screening at the end of March. We are cautiously optomistic but can't keep doing this to ourselves.We have been in genetic counselling and have been told that both of our previous losses were freak occourances. We are not carriers and they told us there is no reason not to try again. Here's to our last chance.

caddychic - 86 days ago.
My husband is a carrier of a rare genetic disorder called Trisomy 4p. He has 2 sisters that are affected by this, He is a carrier, and his mom is a carrier. Our 4 year old was diagnosed with this disorder but the don't know how it is going to affect her later in life. Right now she has delays in speech, she is tiny, and has a few little quirks. She is the greatest thing in the WORLD. I am 34 weeks pregnant now with our 2nd daughter and from u/s 's they are suspecting that she will have the same thing. I opted out of all of those tests because my daughter is so wonderful that it wouldn't make a difference to me. I just hope that the new baby doesn't have anything more severe than our 4 year old.

kaygee - 97 days ago.
I'm 6 weeks pregnant, waiting till the 11th for my first scan, then I will see if this pregnancy is growing normal. I have chromosome disorder which leads to early miscarridge.

lifigirl - 129 days ago.
the post of oct 28 about describing what it's like to have a disabled child is spot on we have one such special child when she was born and was eventually diagnosed i went into a kind of mourning this was for baby i didn't have i almost felt like my child theoone of my dreams had died but not for one minute did we ever not love or want her it's true when you look truly look at my child you see that she has all the bells and whistles and shiny buttons and bows just like everyone else you just have to look abit closer and you know what she gives so much more because she tries so much harder every tiny thing she does is magic and such an achievement every day she makes me proud to be her mum..

mama40 - 140 days ago.
if you just took your pregnancy test, you quite possibly are having your implantation going on right now. It often accompanies with bleeding, that is why some girls don't know they are pregnant until the next period. Don't worry.

banji - 140 days ago.
Hi guys, I had a pregnancy test this morning and it was positive, but I just saw a little blood, what should i do please help..

FirstTimer - 163 days ago.
Crystal405 - The doctor should have respected your wishes regarding no testing. However, they are there to give their professional option, likely encounter women that later change their minds once there are concerns, or perhaps push due to potential liability. IMO - and this is only my opinion - but some infants with some of the most serious chomosomal problems suffer greatly after birth only to die hours, weeks, or months later with their primary experiences being medical tests/surgeries. Of course, it is up to each individual what is right for them and their baby.

crystal405 - 163 days ago.
Hi all. I received a call from my dr. yesterday regarding my ultrasound...that was 2 WEEKS ago. He said there was some concern with the thickness of the skin on her neck?!?! Is this the nuchal translucency? And that it could somehow be linked to the chromosomal defect in down's syndrome. But the result wasn't abnormal, just in the 'high' normal range (2.6mm and I was 20 weeks at the time of my u/s), and he suggested the quad screening...AGAIN...which i already refused (and I thought couldn't be done after 16 weeks), quite a few times. For some reason, he keeps pushing me to get this testing done, and I DON'T WANT IT! He told me not to worry, but suggested having the testing to be sure. Now I'm a wreck and completely stressed out. I want to enjoy this pregnancy, and I'm keeping my lil girl no matter what, which is why I opted not to have the quad testing done in the first place. I don't know why, but he doesn't seem to like the idea that I refuse to have this done. Anyone else have this happen? So, I went for my regular monthly appt. today, and my dr wasn't even there...NO doctor's were, and i had to reschedule...the receptionists apologized and said it was an 'oversight' on their part. Don't know what to do =( Or even what I should do...or what my options are, since my dr. wasn't even around for me to talk to about it. Should I not worry so much, or is there reason for concern? Please help!!

sherrybabydean - 178 days ago.
I learned the hard way when you're told your amnio came back perfect that it dosn't mean a perfect baby.My unborn son had sutures in his head close prematurely.This has caused a disproportioned head that will require surgeries,one right after birth.Brain damage will most likely occure if the surgeries are not done.Ther isn't anything wrong with my husband and I genetically.This is like a 1:50,0000 occurance!The docters are very optimistic and so are we!I love my baby,all of him!

aPRILLOVESWES - 195 days ago.
This is something I saw on another persons page........ WELCOME TO HOLLAND by Emily Perl Kingsley. c1987 All rights reserved I am often asked to describe the experience of raising a child with a disability - to try to help people who have not shared that unique experience to understand it, to imagine how it would feel. It's like this...... When you're going to have a baby, it's like planning a fabulous vacation trip - to Italy. You buy a bunch of guide books and make your wonderful plans. The Coliseum. The Michelangelo David. The gondolas in Venice. You may learn some handy phrases in Italian. It's all very exciting. After months of eager anticipation, the day finally arrives. You pack your bags and off you go. Several hours later, the plane lands. The stewardess comes in and says, 'Welcome to Holland.' 'Holland?!?' you say. 'What do you mean Holland?? I signed up for Italy! I'm supposed to be in Italy. All my life I've dreamed of going to Italy.' But there's been a change in the flight plan. They've landed in Holland and there you must stay. The important thing is that they haven't taken you to a horrible, disgusting, filthy place, full of pestilence, famine and disease. It's just a different place. So you must go out and buy new guide books. And you must learn a whole new language. And you will meet a whole new group of people you would never have met. It's just a different place. It's slower-paced than Italy, less flashy than Italy. But after you've been there for a while and you catch your breath, you look around.... and you begin to notice that Holland has windmills....and Holland has tulips. Holland even has Rembrandts. But everyone you know is busy coming and going from Italy... and they're all bragging about what a wonderful time they had there. And for the rest of your life, you will say 'Yes, that's where I was supposed to go. That's what I had planned.' And the pain of that will never, ever, ever, ever go away... because the loss of that dream is a very very significant loss. But... if you spend your life mourning the fact that you didn't get to Italy, you may never be free to enjoy the very special, the very lovely things ... about Holland.

flgrl - 210 days ago.
Wow! I almost started crying while reading some of these posts. I just had my blood work done on Tuesday to test for abnormalties. I must say Im quite nervous but reading some of these post just reassured me that even if it were to come back abnormal, I'll still love my baby just as much. The post from Laura 'And to any one else who worries about chromosone problems, dont, youll just have a very different mommy experience, but by no means less rewarding!!' really touched me Thanks!

lisak - 211 days ago.
We decided not the have the early screen done and now maybe I'm regretting that. At our 20 wk u/s the doc said the nuchal fold measurement is .47 above normal. He said that he personally wasn't worried because everything else appears normal to him. He even took a 3D image to check the babies facial features. But why the heck would he tell us that there is increased risk of Downs if he thinks everything is fine!!!? He offered that we could have an amnio done if we want to, and I can't decide. On one hand, I trust his judegment on the other hand I can't stop wondering why he would bring it up and want to be sure that everything is in fact fine... Any thoughts on what a .47mm above normal reading may REALLY mean?

Jess G - 225 days ago.
luvbugkw - same with my brother. He's got partial trisomy 18. A little extra piece of chromosome on the 18th. He's 11 now, but at about 7yr old level. They said they didn't know if he'd ever walk/talk/etc...but he progresses everyday. He can walk/talk...and he can even read(which is shocking)...only at about 2nd grade level, but he can. He's not real great with math...but he can write also. Everything he does is a miracle. He's the sweetest guy ever too. So precious. I'm a carrier of the problem he has...so I was sooooo thankful when my daughter was born perfectly normal.

luvbugkw - 226 days ago.
MY NIECE HAS A CHROMOSOME DISORDER WHERE SHE IS MISSING HER 5TH, SHE IS THE SWEETEST MOST LOVEABLE AND BEAUTIFUL CHILD. SHE IS 4 BUT IS AT A LEVEL OF A 2 YR OLD. THEY SAID SHE WOULD NEVER WALK, OR TALK AND SHE IS DOING BOTH, MAYBE NOT AS WELL AS OTHERS BUT IS GETTING MORE ADVANCED EVERYDAY.

liz bee - 238 days ago.
Hello, I had my first child two and a half years ago when I was 33 years old. When I went for my AFP test, they told me that I had elevated AFP levels. Because I was aready at twenty weeks, I decided not to have the amnio which was reccomended. I decided that if this child that i was carrying had a chromosonal disorder, I would deal with it. When Angelo was born, he had Downs Syndrome. I cannot say that it was easy for my husband and myself but we were plugging along trying to adjust to the fact that our new beautiful baby boy had a disability. When Angelo was about two and a half months old, he had an allergic reaction to the formula he was drinking, this gave him severe diareah. I brought him to the pediatrician that morning and the Doctor said that Angelo was having an allergic reaction, take him home and give him soy milk. After we were home for about an hour, he started to have trouble breathing and then he just stopped breathing. We called an ambulance but it took them so long to get there. WHen they finally came, while we waited for them, we administered CPR. When they finally got there, they tried to get a heart beat back but could not for over an hour. When they finally did get him back, he showed no brain activity. He lasted throughout the night until the next morning when his heart started to give out. My husband and I held him close while he took his last breaths. It was devistating to both of us and our families. We waited a couple of years before we started trying again. We have been in therapy together for that whole time and we continue to see our therapist who is the greatest woman ever. I do not think our marriage would have survived this event without her support. I am now 7 months pregant with our second son whose name is Dominic. We have had every test done that was possible and knok on wood, everything has been great. We are so excited. I already have his room all ready and you can see it in the nursery rooms gallery. It is stunning. I cannot wait to meet Angelo's little brother! My husband and I cannot wait to welcome this precious gift to our home. I have had some anxiety throughout this pregnancy as I am sure you can understand. It has been bitter sweet. I hope that everyone who has been through this or is going through this knows that there is a light at the end of the tunnel. Happiness will be there again...thanks for reading...liz

Jess G - 239 days ago.
hi! I'm a carrier of chromosomal abnormality. I have an inversion of the 18th chromosome. I have 50/50 chance of passing to my child and them be a carrier and 10-15% risk of having an affected child. My half brother was born with PARTIAL TRISOMY 18. My half sister is a carrier like I am. I just gave birth to a little girl in June. I was recommended for amnio and didnt' want it...I had her genetically tested at birth, thank God, she's healthy and normal!! But I was scared.


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