Human Karyotypes and Chromosomal Disorders

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Human Karyotypes and Chromosomal Disorders
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Looking At Chromosomes

• We can see chromosomes on a picture called a
  karyotype.

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Karyotype

• Photograph of chromosomes
• Grouped in order of homologous pairs
• Chromosome 1 is the longest and chromosome 22
  is the shortest.

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Making a Karyotype

• During prophase of mitosis
• biologists take pictures of the chromosomes
• Biologist then cut out the chromosomes and match
  them up with their corresponding sister chromatid
  starting with chromosome 1 (the longest
  chromosome).

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Importance of Karyotypes

• Allows a biologist to see if there are problems
  with the chromosomes themselves.
• i.e. extra chromosomes, parts missing, extra
  parts added.
• It helps make a diagnosis of a particular
  condition
• does not determine severity of condition.

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Autosomes

• Chromosomes 1-22
• Non-sex chromosomes

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Sex Chromosomes

• 23rd Pair of chromosomes
• XX female XY male

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The X and the Y

• The X chromosome is almost three times as long as
  the Y chromosome.

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Sex DeterminationIn Humans

• Presence of a Y chromosome leads to maleness
• Father determines sex of child

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Important!!

• Females can only donate an X
• All Female eggs have one X chromosome in them.
• Males can donate one X or one Y.
• The percentage is 50 X or 50 Y.

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Determining Male and Female on a Karyotype

• Look at the 23rd chromosome location.

• Females will have two long chromosomes.
• Males will have a long and a short.
• Usually labeled as X and Y

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Answer in your notes.
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Answer in your notes.
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Notation

• How do you write what you see on a karyotype?
• Look at number of chromosomes 46
• Look at the sex male or female
• Write number then male/ female chromosomes
• 46, XX or 46, XY

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Notation 46, XY
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Chromosomal Disorders
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Nondisjunction

• Chromosomes segregate in meiosis,
• sometimes they do not segregate properly.
• The most common error in meiosis occurs when
  homologous chromosomes fail to separate
  NONDISJUNCTION!
• Abnormal numbers of chromosomes may find their
  way into gametes (egg and/or sperm).

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Down Syndrome Trisomy 21

• 3 chromosomes in the 21st position
• An extra chromosome is a called a trisomy
• Causes mental retardation and susceptibility to
  diseases

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• It affects over 350,000 people in the United
  States alone and is the most common (1 in 800
  live births) imbalance in the number of autosomes
  in people.

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Signs at Birth

• Low muscle tone (babies appear "floppy")
• Flat facial features, with a small nose
• Upward slant to the eyes
• Small skin folds on the inner corner of the eyes
• Hyperflexibility (excessive ability to flex
  joints)
• Enlarged tongue that tends to stick out.

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Risks

• The risk of Down syndrome increases with age,
  from about 1 in 1,250 for a woman at age 25, to 1
  in 1,000 at age 30, 1 in 400 at age 35, and 1 in
  100 at age 40.

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Patau Syndrome-Trisomy 13

• It is a syndrome with multiple abnormalities,
  many of which are not compatible with life.
• Almost half of the affected infants do not
  survive beyond the first month, and about three
  quarters die within 6 months.
• 1 in every 5,000 births

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Signs of Patau

• Cleft lip and palate
• Mental retardation due to altered brain formation
• Congenital heart defects
• Close eyes or one eye, small eyes
• Deafness

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Extra Finger.
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Edwards Trisomy 18

• Extra 18th chromosome
• The syndrome has a very low rate of survival
  resulting from
• heart abnormalities
• kidney malformations
• other internal organ disorders.
• Most die within the mother.

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• The incidence of the syndrome is estimated as 1
  in 3,000 live births.
• The incidence increases as the mother's age
  increases.

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Sex Chromosome Disorders
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Turners Syndrome

• Female inherits only 1 X chromosome 45, XO
• This condition is an example of a monosomy the
  presences of one chromosome where there should be
  two.
• Incidence - 12000 live female births. 

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• Symptoms include
• short stature
• lack of ovarian development
• webbed neck
• arms that turn out slightly at the elbow
• low hairline in the back of the head

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Turners Karyotype
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Webbed Neck, low hair line. Arms that turn out
slightly at the elbow.
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Klinefelter Syndrome

• Men and boys with Klinefelter Syndrome have a Y
  chromosome and 2 X chromosomes. This is an
  example of trisomy. 47, XXY
• This is also a problem of nondisjuction.
• Klinefelter Syndrome occurs in 1 in 500 to 1 in
  1000 live births.
• Develop as males with subtle characteristics that
  become apparent during puberty.
• Tall and usually do not develop secondary sex
  characteristics such as facial hair, or underarm
  and pubic hair

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Symptoms/Signs

• Tall (around six feet)
• small testes or hypogodanism
• inability to produce sperm
• sparse facial and body hair
• gynecomastia
• low energy
• low self esteem
• motor skill issues
• developmental delays
• infertile

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Practice Problems
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