Chromosomes

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Chromosomes Karyotypes

• Genetics

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What is a Chromosome?

• A LONG strand of DNA.
• Organisms that reproduce sexually (two parents)
  receive half of their chromosomes from their
  mother and half from their father.
• Humans have 46 chromosomes (23 from each parent).
• When you have a child, you will contribute 23
  chromosomes!

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Karyotypes

• We can make a picture of what your chromosomes
  look like! This is called a karyotype.
• Each pair of chromosomes is called a homologous
  pair.
• Doctors can use the karyotype to determine is
  certain birth defects are present.
• Also, you can use it to tell if you are a boy or
  girl.

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The 23rd PAIR

• Your 1st through 22nd pair of chromosomes are
  called autosomes. They control traits that are
  NOT sex related.
• Your 23rd pair of chromosomes are called sex
  chromosomes because they tell whether you are
  male or female.
• If you have 2 X chromosomes, you are female.
• If you have 1 X and 1 Y, you are male.
• However, ALL humans start out female. Its not
  until the 2nd or 3rd month of pregnancy that the
  male hormones kick in and turn the baby male.
  This is why boys still have nipples, even though
  they dont breast feed babies!
• Sometimes the male sex hormones dont kick in
  completely and the baby is called intersex. This
  means that even though it is an XY or an XX it
  could have both male and female characteristics.
  This is about as common as having red hair!

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Sex Chromosome Abnormalities

• Sometimes, people are born with sex chromosome
  abnormalities.
• For example, a female can have Turners Syndrome
  if they are born with only one 23rd chromosome
  (an X). This can possibly result in short
  height, heart defects, and infertility.
• A male can have Klinefelters Syndrome if they
  are born with an extra X chromosome (XXY). This
  can result in low testosterone levels which can
  affect growth, puberty, and fertility.

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The 21st Pair

• Sometimes babies are born with an extra 21st
  chromosome. This results in Downs Syndrome,
  sometimes called Trisomy 21.
• The probability of having a baby affected by
  Downs Syndrome increases with the age of the
  mother. A mother is termed a high risk pregnancy
  if she is 35 or older.