Download Apterygota Pterygota: Paleoptera

SCI 355B Lecture 5
Insect Orders (cont.)
Contributions of Insect Research to Our
Understanding of Genetic Processes
Last time:
Apterygota
Pterygota: Paleoptera
Pterygota: Neoptera
Hemimetabolous: gradual
development
Entognathous, Pterygota, Neoptera
Refer to slides from previous handout
(Holometabolous)- Complete Metamorphosis
Order Neuroptera-”lacewings & others”
Order Coleoptera- “beetles”
Order Mecoptera-”scorpionflies”
Order Siphonoptera-”fleas”
Order Diptera- “true flies”
Order Trichoptera- “caddisflies”
Order Lepidoptera- “moths & butterflies”
Order Hymenoptera- “ants, bees, & wasps”
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Insects & Their Contributions
to Genetics
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Genetics
“Branch of biology that deals with heredity
and the expression of inherited traits”
• Heredity - Transmission of traits from one
generation to another
• Trait - any detectable phenotypic
(observable properties of organism)
variation of a particular inherited character
– Discrete: presence or absence; color
– Continuous: height, weight, color
Meiosis
• Cell division which results in halpoid “sex” cells
(i.e., egg and sperm)
• One replication of the genetic material (DNA)
during interphase, but two nuclear divisions
(meiosis I and meiosis II).
• Results in haploid (N) cells (= gametes in animals)
from an initial diploid (2N) cell
• Very similar to mitosis except that the cells
produced are not genetically identical.
Chromosome Structure
sister chromatids
centromere: region of the
chromosome where
chromatids attach.
sister chromatids
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Alleles
A-
a-
B-
b-
C-
C-
Alternative
forms of the
same gene.
Heterozygous
Homozygous
Alleles occur at the same locations (loci) on homologous chromosomes.
DNA Replication during Interphase
A- -A
represents gene A, B- -B
from one parent.
a- -a
b-
-b
Homologous Chromosomes
represents the
same gene from
the other parent,
codes for the
~same protein,
may have a
slightly different
DNA sequence.
Meiosis Prophase I
… Synapsis: the highly specific parallel
alignment of homologous chomosomes
during the first division of meiosis,
A A a a
…tetrad: the two homologous
chromosomes become attached
along their length in a structure
termed a tetrad.
B B b b
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Meiosis Prophase I
cont.
A a A a
B B b b
Crossing Over: rearranges the genes from each parent.
Meiosis Metaphase I -- Telophase I
A a Aa
B B b b
A a
A a
B B
b b
Meiosis Prophase II -- Telophase II
Aa
aA
BB
no DNA synthesis
bb
a
A
A
a
B
B
b
b
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Meiosis is critical for sexual
reproduction in all diploid
organisms
(1) meiosis leads to the formation of gametes.
– gametes (one from each parent) conjugate to form a
zygote.
(2) meiosis is the basis for extensive variation
among members of a population.
Johann Gregor Mendel
(1822-1884)
• Experiments in Plant
Hybridization (1865,1866)
• Had read Darwin’s Origin of
Species (1859) with interest
• Saw no immediate
connection
• Nor did anyone else for
decades
Who was that robed man?
• A monk
• Monastery of St. Thomas
in Czech Republic
• 1884: “I am convinced
that it [my scientific
work] will be appreciated
before long by the whole
world”.
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Mendel’s Contributions
• Identified that genes exist….he called them “unit
factors”
• Indicated that pea plants contain two copies of
each unit factor/gene….we call these alleles.
• Described dominance and recessiveness
• Indicated that the unit factors/alleles segregate
independently. In other words, during gamate
formation (during meiosis) the alleles “go into”
gametes independently of one another.
Monohybrid Cross
Generation
Parental (P)
yellow pea
(pollen)
green pea
(eggs)
x
First Filial (F1)
all yellow
Second Filial (F2)
grow plants, cross
pollinate
grow, allow to selffertilize
6022 yellow : 2001 green
3:1
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Monohybrid Cross
P:
GG
x
F1:
Gg
Gametes:
F2:
gg
G
1/2
g
1/2
(GgxGg)
G
1/2
g
1/2
GG
Gg
gG
gg
1/2 x 1/2
1/2 x 1/2
1/2 x 1/2
1/2 x 1/2
1/4
1/4
1/4
1/4
Dominant vs. Recessive Traits
x
P
F1
The trait that appears in the F1 generation is the DOMINANT trait.
The trait that disappears in the F1 generation is termed RECESSIVE.
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Dominance
Dominance - the interaction of genes (alleles)
at the same locus.
Three Kinds of Dominance
(1) Complete Dominance
(2) Incomplete/Partial Dominance
(3) Codominance
Sex/Gender Determination
Sex-Linked Traits
Sex Determination
• History:
– Medieval Europe (500 - 1500 AD)
• Hammer = boy
• Scissors = girl
– Ancient Greece
• Semen from right testicle
– Rural China and India (present day)
• Female infanticide/sex specific abortion
– Western Societies (present day)
• PGS - preconception gender selection - separate sperm bearing x
and y chromosomes. Usually x-bearing sperm contain ~3%
more DNA than y-bearing sperm
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Sex Chromosomes
• Heteromorphic sex chromosomes - different between the
sexes.
• All mammals have the XY-system
Females:
XX = homogametic sex
Males:
XY = heterogametic sex
Human Male:
46, XY
Human Female:
46, XX
• Karyotype - the chromosome complement of a cell or an
individual. Often used to refer to the arrangement of
chromosomes in a sequence according to size.
Sex Determination
• In mammals, the male sperm determine the sex of
the offspring (X-bearing sperm vs. Y-bearing
sperm).
• Female gametes: 23, X
• Male gametes: 23, X or Y
Other sex determination systems
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ZW System
•
•
•
•
•
Some insects
Some birds (chickens)
Some fish
Same as XY except female is heterogametic
The use of ZW is arbitrary and for distinction
between XY only, but is commonly used in
textbooks
• ZZ = male
• ZW = female
XO Method of Sex Determination
“most insects”
• Some insects (no sex specific chromosome
• Females: XX
• Males: X0 (where 0 indicates lack of 2nd X)
Haplodiploidy (# of whole chromosome sets)
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In Crepidula fornicata, the common slipper limpet, sex is determined
by an environmental factor: the limpet’s position in a stack of limpets.
Sex in the isopod Armadillidium vulgare is usually determined by sex
chromosomes, but genetic males may be converted into functional
females by the presence of infecting bacteria.
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Drosophila melanogaster
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Morgan’s Experiment
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The Double Helix
• On the last day of
February 1953,
according to James
Watson
• Francis Crick
announced to the
patrons of the Eagle
pub in Cambridge
• "We have discovered
the secret of life."
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Gene
• a region of DNA that
controls a hereditary
characteristic.
• It usually corresponds
to a sequence used in
the production of a
specific protein
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Protein Function is Directly Related to the
Structure of the Molecule
• Enzymes (chem. reaction rate)
• Transport (movement of molecules, e.g.,
hemoglobin and myoglobin)
• Structural (e.g., collagen and keratin)
• Binding (histones, hormones)
• Contractile (actin, myosin)
• Immunity (immunoglobulins)
• Etc, Etc, Etc, Etc, Etc, Etc, Etc, Etc, Etc, Etc, Etc,
Drosophila: genetics and development
The key to development lies in the regulation of gene expression.
This early fruit-fly embryo illustrates the localized production of proteins
from two genes that determine the development of body segments.
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Insect Genomes
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