Genetics 321

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Genetics 321

• From Mendel to Genomes

10 Weeks
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Syllabus
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Jeff Young, Botanistyoung_at_biol.wwu.edux3638Offi
ce BI412
Office Hours M, W F 10-11am by appointment.
Arabidopsis thaliana Genome-based study of plant
physiology and environmental responses.
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"I guess there's cool stuff about science,"
Watanabe continued, "like space travel and bombs.
But that stuff is so hard, it's honestly not even
worth the effort."
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Success is Easyif you work hard.

• Do the reading assignments before class,
• pay attention to the figures,
• Come to class,
• study groups!
• Learn the material (know everything).

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Genetics ...the study of the transmission of the
hereditary material.
Classical genetics consists of the techniques and
methodologies of that predate the advent of
molecular biology.
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NucleotidesDNA Bases
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ChromosomesLong Polymers
Phosphodiester Bonds Backbone
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Genomes
... haploid chromosome component of an organism,

• human (23), 3,000 Mb,
• fruit fly (4), 140 Mb,
• nematode (5), 100 Mb,
• mustard (5), 125 Mb,
• yeast (16), 12 Mb,
• bacteria, (1), 5-15 Mb.

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Units of Heredity
chromosome DNA (Mbs long) proteins
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Transmission of Hereditary Materials two keys to
Genetics Meiosis Central Dogma

• ...Meiosis the process of two consecutive cell
  divisions in the diploid progenitors of sex cells.

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Meiosis

• Cell Biology
• ...the mechanism, timing and steps of cell
  division,
• how a cell divides,
• etc.

• Genetics
• a major result of cell division is the
  partitioning of DNA,
• transmission of genomes,
• via the transmission of chromosomes.

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Chromosomesself-replicating genetic structures.

• two copies of each chromosome are present at some
  stage of an eukaryotic organisms life cycle,
• haploid cells carrying one full set of
  chromosomes are termed haploid,
• diploid cells carrying two full sets of
  chromosomes are termed diploid.
• n number of haploid chromosomes.
• 2n diploid number of chromosomes.

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2n 4
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Elements of Variation

• homologous chromosomes a pair of chromosomes
  containing the same linear gene sequence, each
  derived from one parent,
• homologous chromosomes carry the same complement
  of genes,
• the DNA sequence of the genes on homologous
  chromosomes may differ,
• alleles genes at the same location (locus) on
  homologous chromosomes, but that have different
  DNA sequences.

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Meiosis
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n 1 2n 2
Synthesis
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Alleles
Alleles occur at the same location (loci) on
homologous chromosomes.
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Chromosome Structure(cartoons)
M phase
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Meiosis Prophase I

• Synapsis the highly specific parallel
  alignment of homologous chomosomes during the
  first division of meiosis,

tetrad the two pairs of homologous chromosomes
become attached along their length in a structure
termed a tetrad.
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Chiasmata
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Meiosis Prophase I cont.
A
a
A
a
a
A
B
B
b
b
Crossing Over rearranges the genes from each
parent.
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Meiosis Metaphase I -- Telophase I
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Meiosis Prophase II -- Telophase II
Aa
a
A
no DNA synthesis
bb
BB
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Meiosis is critical for sexual reproduction in
all diploid organisms

• ...meiosis leads to the formation of gametes,
• gametes (one from each parent) conjugate to form
  a zygote,
• ...meiosis is the basis for extensive variation
  among members of a population.

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Genetic Recombination Ielement of variation
Crossing over.
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Genetic Recombination II element of variation
2n combinations of chromosomes, n haploid
number of chromosomes.
Random Assortment of Chromosomes.
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2n combinations of chromosomes n number of
chromosomes

• n 1, 2n 2
• n 2, 2n 4
• n 3, 2n 8
• n 5, 2n 32 Arabidopsis
• n 23, 2n 8,388,608 H. sapiens
• n 39, 2n yip! dog

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Mendelian Genetics

• Gregor Mendel (1822-1884),
• Augustinian monk,
• Botanist,

• Pisum sativa,
• Garden pea,
• 1st Model System.

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Model Systems

• Modern biology depends largely on the ability to
  study simple organisms, and then apply the
  resulting principles to more complex systems,
• i.e., ask simple questions about immensely
  complex processes,
• the answers are often simple, though not obvious.

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Tomorrow

• More Mendel,
• Master Chapter 2,
• Review (for mastery) Chapter 4,
• Look at the Problem Set and assigned problems.