What is a chromosome?

A chromosome is a large ''bundle'' of genetic material containing tens of thousands of DNA sequences. These sequences make up individual genes, and each chromosome has many, many genes within it. We all have 46 chromsomes including two pairs of sex chromosomes: X denoting female and Y denoting male. So XY is male and XX is female. There are chromosomal sydromes in which there are too few or too many chromosomes. For example, in Down''s syndrome, there is an extra chromosome 21 (trisomy 21), making 47 chromosomes in total. In Turner''s syndrom (45XO), there are 45, ie one X chromosome is missing.

What is an invasive prenatal test?
Under what circumstances should I have an HIV test?
What is a 'triple test' for Down's Syndrome?
My parents are both from Mediterranean countries and I have been offered a ''haemoglobin electrophoresis'' test; what is this?
How good are the screening tests for Down's?
Can an amniocentesis damage my baby?
How can cytomegalovirus (CMV) affect the baby?
Can cytomegalovirus (CMV) be diagnosed by special tests?
My twins are thought to be dichorionic on the scan at 12 weeks. What is dichorionic?
What is the integrated test for Down's?
What is fetal alcohol syndrome?
If no-one in my family has had Down's syndrome, does this mean that my risk of having a Down's baby is low?
I developed diabetes in my last pregnancy. What tests can I have this time to see if I get it again?
What is HIV?
My friend had a 'nuchal' scan to check for Down's. How does this scan work?
Can I have a photo of the baby at my scan appointment?
Are scans totally safe for the baby?
What is invasive prenatal diagnosis?
Is a CVS (chorion villus sampling) more risky than an amniocentesis?
I have had bleeding ever since my CVS a week ago. Is this normal?
Should I have any screening or diagnostic tests for Down''s?
My blood group is Rhesus negative: can this be a problem for my baby?
My doctor wants to test me for diabetes. Why is it important?
I carry the sickle cell anaemia gene, as does my partner. What does this mean, and what is the risk of my baby having sickle cell disease?
Is it possible for a twin to be missed on an ultrasound scan at 9 weeks?
Is it possible for a twin to be missed on an ultrasound scan at 9 weeks?
Can you explain what blood group means?
Why is my urine checked all the time, and what is it checked for?
Why is it important to check if I''ve had German Measles (rubella)?
How and when do I need my blood pressure checking?
How are invasive tests done and how long do the results normally take?
How do I find out if a nuchal fold scan is available in my area, and at what stage in pregnancy to have one?
My baby's umbilical cord has 2 blood vessels instead of three and I have to go for a further ultrasound scan. Is there cause for concern?
I'm 10 weeks now and have used antibiotics and painkillers during the early part of my pregnancy. Is there anything that can be done to check for fetal abnormalities?
I'm 16 weeks pregnant and as my triple blood test has given a high risk for Down's syndrome, I've been advised to have an amniocentesis. Why can't I have a nuchal scan instead?
My rubella test came back positive, I was told that this is a good thing while I am pregnant because this means that I don't have it and I don't have to worry about passing it to my baby. Is this true?
Can a pap smear test damage an early pregnancy?
How early can baby's sex be identified from a scan?
What is an OSCAR test for Down's?
Is a 3D scan better than a 2D scan?
At what stage can the baby's sex be known?
I'm 22 weeks and have been told that no further scans are scheduled. Is this OK?
Are we able to find out the sex of our baby at our 17 week scan?
What does testing positive to IgG Antibody to Rubella virus mean?
Can you tell if you are having twins when you do your first ultrasound scan?
At my scan there wasn't any fluid in baby's stomach. I went back 20 mins later and still no fluid. What does this mean?
Is it safe for a pap smear to be taken if you believe you may be pregnant?
I am 21 weeks pregnant and was told yesterday that my placenta is low; I'm rescheduled for another ultrasound at 33 weeks. I have no bleeding-is there anything else I should be looking out for?
I am 9 weeks and am taking Lamictal 100g x 2 daily for my epilepsy. I have heard all sorts of stories of how these drugs can effect the baby so I am desperate to know if my baby will be OK?
I'm currently 32 weeks pregnant with my second baby and I have too much amniotic fluid. My current AFI is 23.4 and I'm due to be scanned in a weeks time. There are no apparent reasons for this fluid as baby is on the 75th centile and is swallowing and taking fluid in. All my blood tests have come back negative including GTT and TORCH screen. I have been scared stiff by various doctors telling me I may go into premature labour with various complications such as placental abruption and prolapsed cord. Please tell me something positive!
I am 13 weeks and having a scan this week, is it possible to tell what the sex is?
I can't seem to find the paper which had my ultrasound scan report on, what should I do ?
At my 20 week scan yesterday they weren't able to check baby's heart and brain as the baby was lying "face down". I have to go back in 2 weeks time. Is it common for the baby to be in that position?
Is the anti-D injection safe and would there be any reason for the baby to move more frequently after receiving the injection?
I've had my growth scan and my baby is 3 weeks ahead of itself in growth. What does this mean?
I'm 23 years old and have been told today that my baby has a 1:190 chance of Down's. Im 16 weeks pregnant. Can you give me any advice?
Is paternity DNA testing while pregnant against the law?
I have brittle bones. Will this affect my baby?
Can I get a DNA test done before the baby is born?
I am 3 months pregnant. Is it safe for me to have a CT scan of my brain done?
I am rhesus negative and the dad is positive. My health trust doesn't offer anti-D at 28 and 34 weeks. I am afraid I may become sensitised to rhesus. Is there anything I can do?
I have just had my 20 week scan and it showed the baby was perfect, yet the nuchal fold was 6.3mm. I need to see a consultant in a week, does this mean my baby has Downs?
My blood group is A- (negative) and I had anti-D with my first pregnancy. Will I have it again with my second?
I was 'high risk' for Downs when screening tests were done with my first pregnancy. Will I be high risk with the second?
If the cord is around the neck of the baby, will I have any pain or will I get to know only when I do an ultrasound?
I am 1 weeks pregnant and my triple marker test at 14 weeks gave an "increased risk" for Trisomy 21 (Down's Syndrome). Should I get the triple marker test again at 16 weeks for more accuracy?
I am concerned about my girlfriend's prenancy. She is 13 weeks and the doctors took a measurement of baby's neck skin thickness which turned out to be 3.2 mm. Should I be concerned?
The integrated test for Down's syndrome (nuchal+PAPPA+triple test) has given a low risk result for Down's syndrome, but the triple test component has shown a high risk result. What is the medical significance of this?
If my blood hCG levels are slowly increasing on a weekly basis and I've had vaginal bleeding, is there any chance the baby can survive?
I have just been told at my 20 week anomaly scan that there is a pericardial effusion measuring max 2.4mm. I have been referred for a more detailed scan in 3 weeks time. I know that they normally look for this measurement to be less than 2mm. Is 2.4mm high? What is considered high, medium low?
Do I need anti-D injection if my partner and I are both Rhesus negative?

What is a chromosome?

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