Chapter 2: Genes and Heredity

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Chapter 2 Genes and Heredity

• Genes and Human Reproduction

• By Kati Tumaneng
• (for Drs. Cook Cook)

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Genes and the Magical Four-Letter Code

• Chromosomes Strands of deoxyribonucleic acid
  (DNA) that contain genetic codes.
• Human body has 23 pairs of chromosomes.
• One pair are sex chromosomes XX for females, XY
  for males.
• DNA two strands that twist around each other
  like a spiral staircase. Connect by a series of
  nucleotide bases (Adenine, Thymine, Guanine, and
  Cytosine).

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Genes and the Magical Four-Letter Code

• Gene a segment of DNA that provides an
  instruction for a particular structure, function,
  or trait.
• 30,000 genes aligned along 46 chromosomes each
  gene may contain many thousands of base pairs.
• Estimated 3 billion base pairs in human genome.
• Only approximately 10 of base pairs provide
  active instructions.

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Genes and the Magical Four-Letter Code

• Human Genome Project multinational effort by
  governments and scientist to map the 3 billion
  nucleotide bases and 30,000 genes contained in
  human chromosomes.
• Working draft of human genome completed in 2000
  full genome reported in 2003.
• Still need to determine meaning of base sequences
  and function of genes located.
• When complete, scientist will know the genetic
  markers for every trait disease that can be
  inherited.
• Human Genome Project http//www.genome.gov/1000177
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Genes and the Magical Four-Letter Code

• Could potentially escape devastating effects of
  many genetically determined diseases, but where
  do we draw the line?

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Human Reproduction and Cell Division

• Alleles an alternate version of a gene
  determine the unique traits of each individual.
• Except for mutations, errors in cell divisions,
  and sex cells, every cell contains copy of
  chromosomes that originated at conception.

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Human Reproduction and Cell Division Mitosis

• Mitosis copy division, the type of cell
  division that occurs when chromosomes are copied
  into each new cell.
• Weak base pair bonds unzip.
• Each half forms new DNA strand to link back up
  with old strand.
• Occurs throughout body as it forms and grows.

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Mitosis
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Human Reproduction and Cell Division Meiosis

• Meiosis reduction division, the type of cell
  division that occurs during the formation of
  gametes (sperm and eggs).
• Process reduces chromosomes to 23 in each gamete
  so fertilized egg has 46.
• Ensures diversity in gene pool by allowing
  crossing-over of genetic material across pairs
  and random distribution of chromosomes among
  gametes.

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Meiosis
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Meiosis
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Human Reproduction and Cell Division Meiosis

• Identical twins are the one exception because
  they do have the same genetic codes.
• Monozygotic (MZ) Twins identical twins come
  from same fertilized egg (zygote).
• Dizygotic (DZ) Twins nonidentical twins form
  when two eggs are fertilized by two different
  sperm cells.

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Human Reproduction and Cell Division

• Sex Chromosomes the 23rd pair of chromosomes
  (in humans), specialized to determine the sex of
  the child and other characteristics.
• Sex chromosomes consist of two types X and Y.
• Males are XY and Females are XX.
• When sperm cells form, half have X and half have
  Y chromosomes.
• Sex of offspring determined by which type of
  sperm fertilizes egg.

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• Figure 2.2 on Slide 4 from Cook, J. L., Cook,
  G. (2005). Child development Principles and
  perspectives (1st ed.) (p.44). Boston Allyn and
  Bacon.
• Mitosis on Slide 9 from Cook, J. L., Cook, G.
  (2005). Child development Principles and
  perspectives (1st ed.) (p.51). Boston Allyn and
  Bacon.
• Meiosis on Slide 11 from Cook, J. L., Cook, G.
  (2005). Child development Principles and
  perspectives (1st ed.) (p. 52). Boston Allyn and
  Bacon.
• Meiosis on Slide 12 from Cook, J. L., Cook, G.
  (2005). Child development Principles and
  perspectives (1st ed.) (p. 53). Boston Allyn and
  Bacon.
• All other images retrieved from Microsoft
  PowerPoint Clip Art.