Chromosomes are DNA wrapped around proteins to form an X-shaped
structure. The diagram will help you see the relationship. 1.
Chromosomes are found in the nucleus 2. Chromosomes are made of DNA 3.
Sections of chromosomes are called genes DNA - deoxyribonucleic acid (it
is the genetic code that contains all the information needed to build
and maintain an organism) Each organism has a distinct number of
chromosomes, in humans, every cell contains 46 chromosomes. Other
organisms have different numbers, for instance, a dog has 78 chromosomes
per cell. Somatic Cells - body cells, such as muscle, skin, blood
...etc. These cells contain a complete set of chromosomes (46 in humans)
and are called DIPLOID. Sex Cells - also known as gametes. These cells
contain half the number of chromosomes as body cells and are called
HAPLOID Chromosomes come in pairs, called Homologous Pairs (or
homologs). Imagine homologs as a matching set, but they are not exacly
alike, like a pair of shoes. Diploid cells have 23 homologous pairs =
total of 46 Haploid cells have 23 chromosomes (that are not paired) =
total of 23 Sex Determination Chromosomes determine the sex of an
offspring. In humans, a pair of chromosomes called SEX CHROMOSOMES
determine the sex. If you have XX sex chromosomes - you are female If
you have XY sex chromosomes - you are male During fertilization, sperm
cells will either contain an X or a Y chromosome (in addition to 22
other chromosomes - total of 23). If a sperm containing an X chromosome
fertilizes an egg, the offspring will be female. If a sperm cell
containing a Y chromosome fertilizes an egg, the offspring will be male.
Creation of a Zygote When two sex cells, or gametes come together, the
resulting fertilized egg is called a ZYGOTE Zygotes are diploid and have
the total 46 chromosomes (in humans) Karyotype A karyotype is a picture
of a person's (or fetus) chromosomes. A karyotype is often done to
determine if the offspring has the correct number of chromosomes. An
incorrect number of chromosomes indicates that the child will have a
condition, like Down Syndrome Notice that a person with Down Syndrome
has an extra chromosome #21. Instead of a pair, this person has 3
chromosomes - a condition called TRISOMY (tri = three) Trisomy results
when chromosomes fail to separate - NONDISJUNCTION - when sex cells are
created. The resulting egg or sperm has 24 instead of the normal 23.
Other conditions result from having the wrong number of chromosomes:
Klinefelters Syndrome - XXY (sex chromosomes) Edward Syndrome - Trisomy
of chromosome
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