Human Bio: Chromosomal Inheritance

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Human Bio Chromosomal Inheritance

• Chapter 17

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DNA

• DNA (deoxyribonucleic acid) is a long strand of
  _______________
• Structure
• DNA possesses 4 different bases

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DNA

• DNA is double stranded
• a-helix
• Complementary base pairing
• T ? , C ?

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• The genetic code
• What does the code code for?
• e.g. AATTCGGCTTAA would code for a particular
  protein while GGGTTCCATTAACCG would code for
  another

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Genes

• Every cell type in the human body, except one,
  possesses a nucleus that houses DNA
• Do different cells possess different DNA?

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Genes

• Cellular gene expression
• Chromatin structure
• All cell types, except 3
• Those 3 cells

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• Genome
• One chromosome
• In other words

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• All chromes
• Same but not identical?
• For example

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Human life cycle (Ch 17)

• Humans experience growth and reproduction
• Growth __________ ________
• Reproduction __________ _______
• Nuclear division

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Mitosis

• All cells, at some point, undergo mitosis
• Frequency

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Meiosis

• Cell type
• Males
• Females
• Haploid
• When sperm and egg join

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Mitosis

• Growth in humans
• Cloning?

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Nomenclature

• n
• In humans, n ______
• Since most cells have 2 sets of identical
  chromosomes
• diploid

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An example

• A cell has 2 separate chromosomes,
• n
• If the cell is diploid, 2n

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The cell cycle

• The cell cycle is divided into 2 general phases
• Interphase
• If a cell is on a 24 hour cycle

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Interphase

• In addition to its normal activities, a cell
  that is going to divide completes other special
  activities as well
• G1 phase
• S phase
• G2 phase

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• Mitosis takes up very little of the cell cycle
• During mitosis
• Phases

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Mitosis overview

• Phase 1
• Phase 2
• Phase 3
• Phase 4

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Definitions

• Homologous chromosomes
• Chromatids
• Cytokinesis
• Daughter cells

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Mitosis points to ponder

• 1.
• 2.
• 3.
• Mitosis is it legal?

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Meiosis

• Like mitosis, meiosis involves cell division.
• The 4 phases of meiosis resemble the 4 phases of
  mitosis
• Unlike mitosis, daughter cells in meiosis receive
  half the chromosomes
• In meiosis, there are two divisions instead of one

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• Mitosis 2n ? 2n, 2 daughter cells
• Meiosis 2n ? n, 4 daughter cells

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Two divisions

• Meiosis occurs in two divisions meiosis I
  meiosis II
• Meiosis I chromosomes duplicate (each chrome is
  composed of 2 chromatids).
• However, each daughter cell receives one
  chromosome
• These daughter cells are haploid (n)

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• Meiosis II each daughter cell receives one
  chromatid.
• In meiosis I, two daughter cells form. In
  meiosis II, these two daughter cells give rise to
  2 more daughter cells for a total of 4 daughter
  cells.

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Other tidbits

• During meiosis I, homologous chromes physically
  interact and exchange genetic material
• Called crossing over and recombines genetic
  material

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Questions

• Why is crossing over important?
• Where does meiosis occur?

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Gamete formation

• During spermatogenesis, each primary cell gives
  rise to 4 daughter cells (sperm).
• Total production?
• Avg. rate is 400 million sperm daily!

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• During oogenesis, each primary cell gives rise to
  1 viable daughter cell
• Other daughter cells (polar bodies) dont receive
  equal portion of cytoplasm
• Total egg production?
• Some 7 million, but by puberty this number is
  around 400000 (of which 450 will be ovulated)

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• During fertilization, the sperm and egg (both n)
  contribute 1 set of chromes
• The fertilized egg is now 2n
• That is why everyone receives half their genes
  from the mother and half from the father

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Inheritance

• Karyotype visual display of individuals
  chromosomes
• Autosomes 22 non-sex chromes
• Sex-chromes 23rd pair, X ?, Y ?
• Abnormal number of chromes leads to syndromes

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Autosomal Syndromes

• Nondisjunction occurs during meiosis, when sister
  chromatids fail to separate.
• The result is one gamete(s)/daughter
  cell(s)/egg(s) will have one extra chrome and the
  other(s) will have none

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• Trisomy 21 (Down Syndrome).
• Distinctive physical characteristics and (often
  severe) retardation
• Mothers lt 40 1 in 800, mothers gt 40 1 in 80
• Gene for Down is on 21st chrome, when paired,
  traits are masked

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• Cri du Chat (cats cry) Syndrome.
• Distinctive (facial) characteristics and
  vocalization
• 1 in 50000 births
• Portion of chromosome 5 missing

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Sex chromosome Syndromes

• Turner XO
• Klinefelter XXY
• Poly-X XXX, XXXX, etc.
• Jacob XYY
• Fragile X