Transcript Chapter 2 – Chromosomes and Sexual

Chapter 2 – Chromosomes
and Sexual Reproduction
Basic Cell Types - Prokaryotic
• “before nucleus”
• Unicellular
• Simple structure
– No internal membranes
• Eubacteria
– “true bacteria”
• Archaea
– “ancient bacteria”
– More closely related to
eukaryotes
Basic Cell Types - Eukaryotic
• “true nucleus”
• Unicellular or
mutlicellular
• Large, complex
– Have internal
membranes
Genetic Material
• Prokaryotes
– Single, circular
chromosome
• May have small,
accessory plasmids
– Eubacteria
• DNA within cytoplasm
(nucleoid region)
– Archaea
• DNA may have associated
protein (histones), but
different from eukaryotic
chromosomes
• Eukaryotes
– Multiple, linear
chromosomes
– DNA with associated
histone proteins
• Chromatin
• Chromatin arranged in
specific complex to form
chromosomes
– Allows for packaging
within a small nucleus
Genetic Material - Viruses
• Protein coat
surrounding nucleic
acid (DNA or RNA)
• Not classified as living
organism
– Dependent on host
cell for reproduction
– Evolved after cells
– Closely related to host
• Similar genes
Cell Reproduction - Prokaryotic
• Binary fission
• Origin of replication
– Initiation site of DNA
replication
• 2 DNA molecules move to
opposite ends of cells
– Proteins bind near
replication origins and
anchor new DNA
molecules to plasma
membrane
Cell Reproduction - Prokaryotic
• New cell wall forms to
produce 2 cells
• Identical to each
other, and parent cell
• Asexual reproduction
Cell Reproduction - Eukaryotic
• Chromosomes
– Each species has a
characteristic number
– Diploid cell/organism
• Has 2 copies of each
chromosome
• Homologous
chromosomes
– Save same genes at
same locus
– May have different
alleles
– Haploid cell/organism
• One set/one copy of each
chromosome
Chromosome Structure
• 3 components of a
functional chromosome
– Centromere
• Attachment point for
microtubules
• Kinetochore – protein
complex attached
– Telomere
• Ends of linear
chromosomes
• stabilize
– Origins of replication
• 2 identical copies of DNA
= sister chromatids
– Held together by
common centromere
Chromosome Classification
• Classified by location
of centromere
• “p” arm and “q” arm
• Humans do not have
telocentric
chromosomes
Cell Cycle
• Interphase
– Extended period of
growth
• Mitotic phase
– Mitosis
– Cytokinesis
• Key areas are
regulated at
checkpoints
Interphase
• G1
• S
• G2
Mitosis
• Nuclear Division
• 5 stages
– Prophase
– Prometaphase
Mitosis
• 5 stages con’t
– Metaphase
– Anaphase
Mitosis
• 5 stages cont
– Telophase
Movement of Microtubules
Cytokinesis
• Division of cytoplasm
– Animal cells – cleavage furrow
– Plant cells – cell plate
• Usually occurs simultaneously with telophase
• End result of mitosis/cytokinesis is 2 identical
cells
– Asexual reproduction
Sexual Reproduction and Genetic
Variation
• Meiosis
– Creates gametes/sex cells/egg and sperm
– Chromosome number is reduced by half
• Diploid to haploid
• Fertilization
– Fusion of egg and sperm to restore diploid condition
• Forms diploid, single cell - zygote
– Sexual reproduction
• 1 or 2 parents
Meiosis
• One DNA replication followed by two
rounds of division
• Meiosis I
– Reduces number of chromosomes
• Diploid to haploid
• Meiosis II
– Separates sister chromatids
Meiosis I
• Prophase
Sub-Stages of Prophase I
Meiosis I
• Metaphase
• Anaphase
Meiosis I
• Telophase
• Interkinesis
– Nuclear envelopes are reformed and spindle breaks
down
• Some cells skip to
metaphase II
– Cell may or may not split
into two cells
Meiosis II
• Prophase
• Metaphase
Meiosis II
• Anaphase
• Telophase
Consequences of Meiosis
• End result is 4 haploid cells from one diploid cell
– Each is genetically different
• Crossing over
– Exchange between homologous chromosomes
– Sister chromatids are not identical
• Random assortment
– Shuffles maternal and paternal chromosomes in
different combinations
– Metaphase I
Crossing Over and Random
Assortment
Separation during Mitosis
• Cohesin holds sister
chromatids together
– Established during S
– Broken down during
anaphase by separase
• Separase is inactive
during Interphase and
early mitosis
Separation during Meiosis
• Cohesin aids in formation
of synaptonemal complex
• Anaphase I
– Cohesin broken down by
separase
– Centromeric cohesin is
protected by shugoshin
• Keeps sister chromatids
together
• Metaphase II
– Separase breaks down
shugoshin
• Allows separation of sister
chromatids
Meiosis in Animals
Alternation of Generations in Plants