Instructor

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Instructor
Dr. Ken W.Y. Cho (kwcho_at_uci.edu) Office Rm 4
213, McGaugh Hall Office Hour Wednesday 1200-1
00

http//darwin.bio.uci.edu/cholab/
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Development
Generation of orderly, recognizable patterns as a
consequence of the formation of new constituents
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Development is a unified process
1) growth enlargement (increase in total mass)
2) determination process by which a cell or part
of an embryo become restricted to a given pathway
3) differentiation actual appearance of new
properties
4) morphogenesis generation of a new shape
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MEIOSIS AND MITOSIS
Living cells need to propagate
Cell division is required A compl
ete set of cytoplasmic and nuclear processes has
to be coordinated with one another during the
cell cycle
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Germ Cells and Fertilization
Chapter 20
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Asexual reproduction

• Simple and direct
• Offspring are genetically identical to the
  parents

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Sexual Reproduction

• Sexual reproduction offspring differ genetically
  from one another and from both their parents
  
• mixing of the genome.
• create new combination of genes
• requires haploid/diploid generation of cells.

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• Reshuffling of genes in sexual reproduction
  helps a species to survive in an unpredictably
  variable environment.
  
• Sexual reproduction allows
• many deleterious mutations to be eliminated
• permit the rare advantageous mutations to be
  combined in a single individual.

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• Somatic cells any cells of a plant or animal
  other than a germ cell
  
• Gametes precursor cells that will give rise to
  gametes
  

A haploid gamete must be produced from a diploid
cell in meiosis.
EGG AND SPERM CARRY HAPLOID CHROMOSOME NUMBER
(N)
haploid chromosome a basic chromosome set
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Autosomes Any chromosomes other than sex
chromosomes. Sex Chromosomes chromosomes that
may be present or absent according to the sex of
the individual.
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Genetic recombination (maternal/paternal
chromosome exchange) occurs
Note the way maternal and paternal chromosomes
segregate.
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Nondysjunction chromosomes fail to separate into
4 normal haploid cells. In human female, the erro
r rate is high (10 of meiosis)
failure of the segregation of chromosomes
Down's syndrome
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• Prophase I
• Pairing of homologous chromosome (cross-over)
  occurs genetic recombination
  
• maternal/paternal chromosome exchange

Sister chromatids are are apposed along the their
entire length. Chiasma a site of crossover betwe
en two nonsister chromatids
Cohesins proteins that hold sister chromatids
together along their length before their
separation.
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Recombination can occur several times
Pairing of sex chromosomes Crossovers are possib
le because a small region of homology exists
between the X and the Y.
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• Forms bivalent
• 4 chromatids
• Forms fused kinetochores of sister chromatids

Maternal and paternal chromosomes segregate into
different daughter cells.
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Unless they are identical twins, no two offspring
of the same parents are genetically the same.

• Independent assortment random distribution of
  the maternal and paternal homologs between the
  daughter cells.
  
• 2(23)8.4 x 10(6).
• 2. Crossing over occurs in prophase I.
• 2-3 crossover events occur on each pair of
  human chromosomes.

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A series of complex events occurs during prophase
of meiosis division I homologous chromosome
pairing initiated.
Synaptonemal complex
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Leptotene condensation of chromosomes
Zygotene development of synatonemal complex
Pachytene completion of synapsis
Diplotene chromosome decondensation
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A large protein complex that sits on the
synaptonemal complex (contain Rad51, a recA like
protein)
early nodule frequently seen, present before
pachytene late nodules less frequent, present
during pachytene
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Prophase I occupies 90 or more of the time taken
by meiosis

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The crossover events do not occur uniformly along
the chromosomes. There are recombination hot
spots induced by the meiotic endonuclease
Spo11. Occurrence of one crossover interfere
s with a second occurring at a nearby site.
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Genetic Map Distance between each pair of
neighboring genes is displayed as the percentage
recombination between them.
If two mutant genes are far apart, one or more
crossover will separate them at meiosis.
Frequency of coinheritance of many genes
24 linkage groups have been defined for human (22
plus X and Y).
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cM (centimorgan) a 1 probability that two
genes will be separated by a crossover event
during meiosis. A typical human chromosome is mo
re than 100cM long.
Genetic Map is different from physical distance
map
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Comparison of the physical map and genetic maps
of chromosome I in budding yeast
Note the physical map distance and genetic map
distance are not identical.
A recombination cold spot B recombination hot s
pot