Transcript ENVI 30 Environmental Issues

I.
Control of Cell Cycle
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Normal growth & development require
control of cell cycle (timing, location)
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A.
Some cells divide frequently (Ex: Skin cells)
Some cells divide for repair (Ex: Liver cells)
Some cells don’t divide (Ex: Nerve cells)
Checkpoints
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Control points in cell cycle
Three major checkpoints
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G1
G2
M
Fig. 12.15
I.
Control of Cell Cycle
A.
Checkpoints
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“No” at G1 checkpoint directs cell to G0
Most cells in human body in G0 phase
Fig.
12.16
II.
Sexual Life Cycles
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Organisms with sexual life cycles typically contain
two copies of each chromosome
Two basic cell types
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1)
Somatic cells
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2)
Gametes
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Diploid (2n) – Two complete sets of chromosomes
Chromosome set includes n-1 autosomes & 1 sex
chromosome
Pairs of autosomes = homologous pairs (same loci)
Females – homologous sex chromosomes
Haploid (n)
Sperm cells, ova
Produced by meiosis
Unite in fertilization to produce diploid zygote
Sexually reproducing organisms alternate between diploid
& haploid stages
Fig. 13.5
Fig. 13.6
III. Meiosis
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Similar to mitosis, except DNA replicated
once before cells divide twice
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Divisions – Meiosis I, Meiosis II
Fig. 13.7
Long, Complex Phase
>90% of meiosis (days)
Synapsis, Synaptonemal Complex
Fig. 13.8
Fig. 13.8
Fig. 13.9
Fig. 13.9
Fig. 13.10
Fig. 13.9
Fig. 13.11
IV. Principles of Inheritance
A.
Historical Background
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First person to study inheritance quantitatively
was Gregor Mendel (1822-1884)
Selective breeding common
Known that
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Hybrid plants with same two parents are similar
Mating of hybrid offspring produces diverse progeny
(primary hybrids don’t breed true)
IV. Principles of Inheritance
Mendel’s Experiments
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Used garden pea (Pisum sativum)
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Easy to grow
Many varieties readily available
Flowers could be pollinated in a controlled manner
Fig. 14.2
IV. Principles of Inheritance
Mendel’s Experiments
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Before experiments, Mendel developed truebreeding lines with consistent phenotypes
Used characteristics that could be studied easily
Strengths of approach
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Clearly-defined traits
Simple experiments
IV. Principles of Inheritance
Mendel’s Experiments
B.
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Prevailing thought: Traits controlled by fluids
that blended together in offspring
Mendel crossed parent plants (P generation)
with different traits
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Produced offspring resembling only one parent in first
generation (F1 generation)
Crossed two F1 hybrids
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Produced offspring (F2 generation) resembling both
grandparents
Fig. 14.3
IV. Principles of Inheritance
Mendel’s Experiments
B.
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Prevailing thought: Traits controlled by fluids
that blended together in offspring
Mendel crossed parent plants (P generation)
with different traits
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Produced offspring resembling only one parent in first
generation (F1 generation)
Crossed two F1 hybrids
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Produced offspring (F2 generation) resembling both
grandparents
Results suggested existence of heredity factors
(genes) with different forms (alleles)
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Dominant trait masked recessive trait in F1 generation
Fig. 14.4
IV. Principles of Inheritance
Mendel’s Model
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Developed hypothesis to explain inheritance
patterns
Alternative versions of genes account for
variations in inherited characters
For each character, an organism inherits two
alleles, one from each parent
If two alleles at a locus differ, dominant allele
determines phenotype; recessive allele doesn’t
affect phenotype
Law of segregation: Alleles separate during
gamete formation; one allele in each gamete
(mechanism?)
Reported findings in 1866; rediscovered in 1900