how could a zygote end up with an extra chromosome
Either the egg or the sperm doesn't divide equally.
Down syndrome is usually caused by a condition known as Trisomy 21, which means that a person has three copies of Chromosome 21, rather than the usual two copies. An extra chromosome is added. The normal amount is 46, but people with Down syndrome have 47.Occasionally, the condition is a result of part of Chromosome 21 becoming fused to the end of another chromosome.More info on Chromosome 21While Chromosome 21 isn't the shortest chromosome, it is the one that contains the fewest genes (other than the Y chromosome). This is because genes on Chromosome 22 are more closely spaced, and thus the chromosome contains more genes, despite its smaller size.
The usual number of chromosomes in a baby's cell ( zygote ) is 46 . 23 chromosomes from both the male's reproductive cell ( sperm ) and the female's reproductive cell ( egg ) .
The X chromosome is generally larger and carries more genetic information compared to the Y chromosome. In the traditional system of organizing chromosomes by size, the X chromosome is placed in group C as it is larger, while the Y chromosome is smaller and simpler, so it is usually placed at the end of the fourth row.
A chromosome with a sub-terminal centromere has its centromere located towards one end of the chromosome rather than in the middle. This can affect the behavior of the chromosome during cell division and can impact genetic inheritance and variability.
Cytoplasm
how could a zygote end up with an extra chromosome Either the egg or the sperm doesn't divide equally.
A normal karyotype will show all 23 chromosomes at normal growth, and the end will show an either XY (boy) or XX (girl). Karyotypes of people with autosomal diseases and other diseases associated with chromosomes will show abnormalities on that certain chromosome. For example, Down syndrome is caused by a whole extra chromosome on chromosome 21. This extra chromosome can be seen on the karyotype.
Down syndrome is usually caused by a condition known as Trisomy 21, which means that a person has three copies of Chromosome 21, rather than the usual two copies. An extra chromosome is added. The normal amount is 46, but people with Down syndrome have 47.Occasionally, the condition is a result of part of Chromosome 21 becoming fused to the end of another chromosome.More info on Chromosome 21While Chromosome 21 isn't the shortest chromosome, it is the one that contains the fewest genes (other than the Y chromosome). This is because genes on Chromosome 22 are more closely spaced, and thus the chromosome contains more genes, despite its smaller size.
I thought they were acrocentric (centromere positioned so close to the end of the chromosome that the short arm of the chromosome is not visible) rather than telocentric (centromere located completely at the terminal end of the chromosome).
The usual number of chromosomes in a baby's cell ( zygote ) is 46 . 23 chromosomes from both the male's reproductive cell ( sperm ) and the female's reproductive cell ( egg ) .
You are born with it>>>>>>>>>>>During meiosis, chromosomes are separated equally. When they are notseparated equally - this is known as non-disjunction - the gametes end up with either an extra chromatid or no chromatid. In Down syndrome the offspring carries an extra chromatid in Chromosome 21, aka Trisomy 21
Trisomy 18 is a form of chromosomal aberration. It is neither recessive nor dominant. Neither does it show co-dominance or incomplete dominance factor. It arises due to the presence of an extra chromosome 18 in the somatic cells.
The X chromosome is generally larger and carries more genetic information compared to the Y chromosome. In the traditional system of organizing chromosomes by size, the X chromosome is placed in group C as it is larger, while the Y chromosome is smaller and simpler, so it is usually placed at the end of the fourth row.
A chromosome with a sub-terminal centromere has its centromere located towards one end of the chromosome rather than in the middle. This can affect the behavior of the chromosome during cell division and can impact genetic inheritance and variability.
Cytoplasm
During meiosis, chromosomes are separated equally. When they are not separated equally - this is known as non-disjunction - the gametes end up with either an extra chromatid or no chromatid. In Down syndrome the offspring carries an extra chromatid in Chromosome 21, aka Trisomy 21.
The chromosome number at the end of meiosis is half of the parent cell