Chromosome abnormalities occur when there are errors in cell division that result in cells having too few or too many chromosomes. There are two main types of chromosome abnormalities: numerical abnormalities like Down syndrome which is Trisomy 21 resulting from an extra copy of chromosome 21, and structural abnormalities where part of a chromosome is missing, duplicated, or rearranged. Chromosome abnormalities usually happen during mitosis and meiosis, the two types of cell division where the number of chromosomes should remain the same or be halved, but errors can cause the wrong number of chromosomes to end up in resulting cells.

1. Heredity and
Chromosomal
Abnormalities

2. Vocabulary
6. Chromosome- a threadlike structure of
nucleic acids and protein found in the nucleus
of most living cells, carrying genetic
information in the form of genes.
7. Mitosis- results in two cells that are
duplicates of the original cell.
8. Meiosis- is the type of cell division that
occurs in the reproductive organs, resulting in
the eggs and sperm.

3. Cells
- are the basic building blocks of
all living things. The human body
is composed of trillions of cells.

16. What are chromosome abnormalities?
Two basic groups: numerical abnormalities and
structural abnormalities.
Numerical Abnormalities: When an individual is
missing one of the chromosomes from a pair, the
condition is called monosomy.

17. When an individual has more than two
chromosomes instead of a pair, the condition is
called trisomy.
Ex: Down syndrome ( Trisomy 21)
Marked by: learning difficulties
poor muscle tone
( hypotonia) in infancy
mental retardation
facial characteristics

19. Down syndrome- has three copies of
chromosome 21 rather than two; for that reason,
the condition is also known as Trisomy 21.
Monosomy, in which an individual lacks a
chromosome, is Turner syndrome. In Turner
syndrome, a female is born with only one sex
chromosome, an X, and is usually shorter than
average and unable to have children, among
other difficulties.

21. Structural Abnormalities: A chromosome's
structure can be altered in several ways.
Deletions: A portion of the chromosome is
missing or deleted.
Duplications: A portion of the chromosome
is duplicated, resulting in extra genetic
material.

22. Translocations: A portion of one
chromosome is transferred to another
chromosome.
Inversions: A portion of the chromosome
has broken off, turned upside down, and
reattached. As a result, the genetic material
is inverted.

23. Rings: A portion of a chromosome has
broken off and formed a circle or ring.
This can happen with or without loss of
genetic material.

24. How do chromosome abnormalities happen?
Chromosome abnormalities usually occur when there
is an error in cell division. There are two kinds of cell
division, mitosis and meiosis.

25. Mitosis- results in two cells that are
duplicates of the original cell.
• One cell with 46 chromosomes divides
and becomes two cells with 46
chromosomes each.

26. • This kind of cell division occurs
throughout the body, except in the
reproductive organs. This is the
way most of the cells that make up
our body are made and replaced.

27. Meiosis results in cells with half the
number of chromosomes, 23, instead
of the normal 46. This is the type of
cell division that occurs in the
reproductive organs, resulting in the
eggs and sperm.

28. Meiosis- is a type of cell division that reduces the
number of chromosomes in the parent cell by half and
produces four gamete cells. This process is required to
produce egg and sperm cells for sexual reproduction.

29. • In both processes, the correct number
of chromosomes is supposed to end
up in the resulting cells.
• However, errors in cell division can
result in cells with too few or too
many copies of a chromosome.

30. • Errors can also occur when the
chromosomes are being duplicated.
• Other factors that can increase the risk of
chromosome abnormalities are:

31. 1.Maternal Age - Some researchers believe that
errors can crop up in the eggs' genetic material as
they age. Older women are at higher risk of giving
birth to babies with chromosome abnormalities than
younger women.
2. Environment-
it is still possible that the environment may play a
role in the occurrence of genetic errors.