Chromosomes and Karyotypes

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Chromosomes and Karyotypes

• What is a Chromosome
• Terminology
• Chromosomal Mutations
• Differences among species
• Karyotypes
• Nondisjunction disorders

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What is a chromosome?

• Chromosome- coils of DNA and proteins
• Chromatid- two exact copies of DNA that make up a
  chromosome
• Centromere- where the two chromatids attach

Chromosome
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Terminology

• Gene- segment of DNA that codes for a protein or
  RNA molecule
• Units of information

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Terminology

• Homologous chromosomes- are chromosomes that are
  similar in shape, size and genetic content

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Terminology

• Somatic cell- any cell other than a sperm or egg
  cell
• Cheek, blood, brain, bone, liver, kidney
• 46 chromosomes in human somatic cells
• 23 pairs
• One set comes from the mother, the other from the
  father
• A diploid (2n) cell contains two sets of
  chromosomes, like the somatic cell

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Terminology

• Gamete- sperm or egg cell
• Carries one set of chromosome (has 23 total
  chromosomes)
• A haploid (n) cell contains only one set of
  chromosomes, like the gamete cell

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Terminology

• Fertilization- fusion of two gametes (fusion of
  sperm and egg)
• Zygote- fertilized egg cell
• The first cell of a new individual

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Terminology

• Haploid (n)
• Diploid (2n)
• n 23
• Sperm 23 chromosomes n
• Egg 23 chromosomes n
• Total 46 chromosomes 2n
  (diploid)

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Chromosomal Mutations

• Mutations- changes in an organisms chromosome
  structure
• Deletions
• Duplication
• Inversion
• Translocation

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Chromosomal Mutations

• Original Chromosome
• Deletion- when a piece of chromosome breaks off
  completely
• Duplication- a chromosome fragment attaches to
  its homologous chromosome

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Chromosomal Mutations

• Inversion- when the chromosome piece reattaches
  to the original chromosome but in a reverse
  orientation
• Translocation- when the chromosome piece
  reattaches to a nonhomologous chromosome

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Chromosomal Mutations
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Differences among species

• Each organism has a characteristic number of
  chromosomes
• The number is constant with the species
• Potatoes, plums, and chimpanzees all have 48
  chromosomes

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Differences among species

• Oats, Raccoon Dogs, Rats, Wheat and Wolverines
  all have 42 chromosomes

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Karyotypes

• A karyotype is a picture of an organisms
  chromosomes
• It allows us to study the difference of shape,
  structure and size of each chromosome

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Karyotypes

• Humans have 23 pairs of chromosomes
• Sex chromosomes- the last pair (23) on a
  karyotype that determine the sex of an individual
• Females (XX)
• Males (Xy)
• Autosomes- are all other chromosomes

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Karyotypes

• During mitosis, a picture is taken
• The chromosomes are sorted into identical pairs
  and arranged from biggest to smallest
• The 2 sex chromosomes are put at the end (pair 23)

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Nondisjunction

• Sometimes during meiosis, the chromosomes fail to
  separate correctly (called nondisjunction)
• Monosomy- when gamete has only 1 copy of the
  affected chromosome
• Trisomy- when the other gamete has 3 copies of
  one chromosome

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NondisjunctionCommon Disorders

• Klinefelters syndrome
• One to several extra sex chromosomes
• Ex. XXY or XXXY
• Turners syndrome
• Only one sex chromosome
• Absense of Y develops into female
• Ex. XO

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NondisjunctionCommon Disorders

• Downs Syndrome
• Autosomal
• Trisomy 21
• Most common birth defect
• Patau Syndrome
• Autosomal
• Trisomy 13
• Rarely live past infancy
• Neurological problems, polydactyl and facial
  defects

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NondisjunctionCommon Disorders

• Edwards Syndrome
• Autosomal
• Trisomy 18
• 30 of babies die by 1 month
• Learning disabilities, congenital heart defects
  and malformations of digestive tract, urinary
  tract and genitals

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