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Chapter 3 Genetics: Reproducing Life and Producing Variation
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Cytology: The Study of Cells
• basic units of life
• Complex life forms are made up of billions of
cells.
• cells of all organisms share many similarities as
a result of their common evolutionary past. Prokaryotic cells: 3.7 billion years old
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Escherichia coli (E. coli)
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• Eukaryotic cells 1.2 billion years old – Multicellular organism are only 600 million years old
Ribosomes
Mitochondria
Nucleus (1)
Cytoplasm (2)
have a membrane-bound nucleus and
distinct organelles.
endoplasmic reticulum
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Two Types of Cells
• Somatic cells are the components of body tissues.
• Gametes are sex cells. Ova (oocytes) are egg cells produced
in female ovaries. Sperm (spermatocytes) are sex cells produced in male testes.
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Two Types of Cells
• Somatic cells are the components of body tissues.
• Gametes are sex cells. Ova (oocytes) are egg cells produced
in female ovaries. Sperm (spermatocytes) are sex cells produced in male testes.
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DNA Molecule: The Genetic Code
The DNA molecule 3 talents:
1. Replicate
2. Synthesize
3. Regulate
Genome
homoplasmic
1953: James Watson
& Francis Crick
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DNA: The Blueprint of Life Nucleotides: deoxyribose sugar, a phosphate group, and one of
four nitrogenous complimentary bases.
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DNA: Replicating the Code
Replication takes
place during
mitosis and
meiosis
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Chromosome Types
• Each species is characterized by a specific number of
chromosomes.
– Humans have 46 chromosomes. (Haploid/Diploid)
• Chromosome pairs are called homologous.
– carry genetic information influencing the same
traits.
– not genetically identical.
• The locus is the location of a gene on a
chromosome. ABO locus is on chromosome 9.
• Alleles, homozygous, heterozygous
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heteroplasmic
Zygote
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• Autosomes - govern all physical characteristics
except sex determination.
• Sex chromosomes - X and Y chromosome
(mammals).
• Karyotype- position of centromere, banding patterns
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Mitosis Mitosis:
Production of
Identical Somatic
Cells
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Meiosis: Production
of Gametes (sex
cells)
• only in the ovaries
and the testes.
Animation
223 = 8,388,608
8,388,608 x 8,388,608
= 70,000,000,000,000
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Evolutionary Significance of Meiosis
• Meiosis (and sex) produce variation
• Faster than mutation.
– The random assortment results in 8 million possible gametes.
• 70 trillion when mating
223 = 8,388,608
8,388,608 x 8,388,608
= 70,000,000,000,000
• Cross- over produces recombination: also provides genetic diversity for natural selection to act on.
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Law of Independent Assortment
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Linkage
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Problems With Meiosis
• Nondisjunction errors
• About 50% of pregnancies miscarry.
– 70% are the result of nondisjunction.
• Down syndrome (trisomy 21) – At age 25, 1 in 1,250
– At age 30, 1 in 1,000
– At age 35, 1 in 400
– At age 40, 1 in 100
– At age 45, 1 in 30
– At age 49, 1 in 10
• Nondisjunction may also occur in sex
chromosomes
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Protein Synthesis
Producing Proteins: The Other Function of DNA
Transcription
Translation
RNA
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Ribosomes
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Peptide bond
Triplets
Codons
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Amino Acids
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Genes: Structural and Regulatory
• Homeotic (Hox) Genes
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Polymorphisms: Variations in Specific Genes
• Locus
• Law of Segregation
• Single nucleotide polymorphisms (SNPs)
• Homozygous and heterozygous
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Polymorphisms: Variations in Specific Genes
• Antibodies
• Antigens
• Codominance
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The Complexity of Genetics: Polygenic Variation and Pleiotropy