How Chromosome Abnormalities Happen: Meiosis, Mitosis, Maternal Age, Environment
4 days ago Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle. Down syndrome occurs when the egg contains an extra copy of chromosome material can also attach itself to chromosome 21 in the sperm. When fertilization occurs, the normal 46 total number of chromosomes results in the fetus. If meiosis does not occur properly, an egg or sperm.
The fertilised egg cell divides rapidly in the womb and eventually the baby is formed.
Down Syndrome (Trisomy 21)
Each of the body cells of the baby also contains 23 pairs 46 chromosomes see Figure 1. When a blood sample of a baby is analysed in a laboratory, a photograph of the chromosomes is taken under a microscope. The chromosomes on the photo are then cut out, numbered and arranged according to pairs.
Such a chromosome arrangement is called a karyotype see Figure 2. Note that the chromosomes are arranged and numbered. One of the smallest chromosomes is numbered as no. It is this chromosome no.
There are different types of Down syndrome, viz. The Trisomy 21 type of Down syndrome Trisomy 21 occurs when the two no.Down syndrome (trisomy 21) - causes, symptoms, diagnosis, & pathology
This cell then has 24 chromosomes instead of the normal This phenomenon of the chromosome pair not separating is called noadisjunction. With fertilisation, the sex cell of one of the parents egg cell or sperm with the two no. The baby that develops from this cell will therefore have an extra no.
The trisomy 21 type of Down syndrome may be caused by non-disjunction during the formation of either the egg cells of the mother or the sperm of the father.
The chances of non-disjunction however seem to be increased in women in their late thirties and older see Figure 4. The cause is unknown, it is important to understand that it is not caused by anything the mother or father did or failed to do during the pregnancy.
- Down Syndrome South Africa
- How Chromosome Abnormalities Happen: Meiosis, Mitosis, Maternal Age, Environment
- Down Syndrome (Trisomy 21)
Trisomy Down syndrome is not hereditary. In young mothers the chance of a second baby being born with Down syndrome is therefore very small.
It seems like every time scientists try to find something that is truly the same for ALL people, they end up finding endless variations. Interestingly, these human differences can be found even at the level of our DNA!
Some of these genetic variations are so small that they are unnoticeable, but some are substantial enough to change the way the body grows and develops.
Causes of Down syndrome | Chromosome 21 | 47 Chromosomes
Where do our chromosomes come from? Chromosomes are the tightly wound strands of genetic material that contain all of your DNA. Typically, babies are born with 23 identical pairs of chromosomes 46 chromosomes in total. Diagram of a typical set human chromosomes Half of your chromosomes come from your mother and half come from your father. Through a process called meiosis each of your parents creates a sex cell either a sperm or an egg that contains half of their chromosomes.
When the sperm cell and the egg cell combine, they create a new fertilized cell how cute!
That cell then starts making new copies of itself, through a process called mitosis, each with 46 chromosomes. Check out this great video on mitosis and meiosis Diagram of mitosis and meiosis What happens with Down syndrome? During both mitosis and meiosis, there is a phase where each chromosome pair in a cell is separated, so that each new cell can get a copy of every chromosome.
This is called nondisjunction. With Down syndrome, various types of uneven chromosome separation result in a person having an extra copy or partial copy of chromosome There are three main types of Down syndrome: When the fertilized egg is developed, it passes along the extra copy of chromosome 21 to every cell in the body.