Download 2n = 47

1
Chromosomes
2
Chromosome Number
 All cells in the human body
(SOMATIC CELLS) have 46 or 23
pairs of chromosomes
 Called the DIPLOID or 2n number
 GAMETES (eggs & sperm) have
only 23 chromosomes
 Called the MONOPLOID or 1n
number
3
Nondisjunction
 Chromosomes may fail to separate
during meiosis
 Resulting gametes may have too
few or too many chromosomes
 Examples of chromosomal
disorders:
 Down Syndrome – three #21 chromosomes
 Turner Syndrome – single X chromosome
 Klinefelter’s Syndrome – XXY chromosomes4
Karyotype
 A picture of a person’s chromosomes
Normal Male
2n = 46
6
Normal Female
2n = 46
7
Male, Trisomy 21 (Down’s)
2n = 47
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Female Down’s Syndrome
2n = 47
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Downs Syndrome
 Set of symptoms that can range from mild to
severe
 Slower mental and physical development
 Flat face with an upward slant to the eye, short
neck, and abnormally shaped ears
 Poor muscle tone, loose ligaments
 Heart disease
 Eye problems
 Intestinal problems
Klinefelter’s Syndrome
2n = 47
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Klinefelter’s syndrome
 Male
 Don’t produce enough testosterone
 Smaller testes
 Breast enlargement
 Reduced body and facial hair
 Most infertile
 Increased risk of breast cancer
 May have learning disabilities
 1 in 500 births
Turner’s Syndrome
2n = 45
15
Turner Syndrome
 Short stature
 Ovaries don’t function correctly
 Won’t go through puberty unless treated
with hormones
 1/3 have extra folds on the neck
 1/3 have heart defects
 1 in 2500 births (many miscarry, though)
Pedigree Charts
The family tree of genetics
What is a Pedigree?
 A pedigree is a chart of the genetic history of
family over several generations.
 Scientists or a genetic counselor would find
out about your family history and make this
chart to analyze.
Constructing a Pedigree
 Female
 Male
Connecting Pedigree Symbols
Examples of connected symbols:
 Married Couple
 Siblings
Example
 What does a pedigree chart look like?
Interpreting a Pedigree Chart
1.
Determine if the pedigree chart shows an
autosomal or X-linked disease.
 If most of the males in the pedigree are
affected the disorder is X-linked
 If it is a 50/50 ratio between men and
women the disorder is autosomal.
Example of Pedigree Charts
 Is it Autosomal or X-linked?
Answer
 Autosomal
Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive.
 If the disorder is dominant, one of the
parents must have the disorder.
 If the disorder is recessive, neither parent
has to have the disorder because they can
be heterozygous.
Example of Pedigree Charts
 Dominant or Recessive?
Answer
 Dominant
Example of Pedigree Charts
 Dominant or Recessive?
Answer
 Recessive
Examples of recessive traits
 Albinism – lack of hair and skin
pigmentation
 Tay-Sachs – fatal disease that causes nerve
damage
 Cystic fibrosis – defective protein needed for
lungs and digestion
Examples of dominant traits
 Achodroplasia – dwarfism – 1 out of 25,000
 Huntington’s disease – degeneration of
nervous system leading to death