Meiosis Chapter 8 Part II. Agenda Textbook: Pages 136-143 Meiosis and crossing over, Pages 181-193...
-
Upload
gwen-newton -
Category
Documents
-
view
215 -
download
1
Transcript of Meiosis Chapter 8 Part II. Agenda Textbook: Pages 136-143 Meiosis and crossing over, Pages 181-193...
MeiosisMeiosis
Chapter 8Chapter 8
Part IIPart II
AgendaAgenda
Textbook: Pages 136-143 Meiosis and Textbook: Pages 136-143 Meiosis and crossing over, Pages 181-193 The crossing over, Pages 181-193 The structure of genetic material.structure of genetic material.PowerpointPowerpoint
Quiz datesQuiz dates
12/7 Germ cell vs Somatic cell, 12/7 Germ cell vs Somatic cell, Meiosis, crossing over, Homologous Meiosis, crossing over, Homologous chromosomes.chromosomes.
12/9 TBA12/9 TBA
Octopus Sex Octopus Sex
Male reaches under his mantle with Male reaches under his mantle with tentacle, removes packet of sperm, tentacle, removes packet of sperm, and insert it into female’s egg and insert it into female’s egg chamberchamber
Eggs are fertilized and give rise to Eggs are fertilized and give rise to new octopusesnew octopuses
Limpet SexLimpet Sex
Larva can become adult of either sexLarva can become adult of either sex
Depends on whether other limpets are Depends on whether other limpets are
present and what their sex ispresent and what their sex is
Adults can change sex in response to Adults can change sex in response to
new arrivalsnew arrivals
Slipper snailsSlipper snails
HermaphroditicHermaphroditic Stacked on top of each otherStacked on top of each other Young are always maleYoung are always male Can stay male or change to femaleCan stay male or change to female Cannot go back to maleCannot go back to male
Sexual ReproductionSexual Reproduction
Chromosomes are duplicated in Chromosomes are duplicated in germ cellsgerm cells
Germ cells undergo meiosis and Germ cells undergo meiosis and cytoplasmic divisioncytoplasmic division
Cellular descendents of germ cells Cellular descendents of germ cells become gametesbecome gametes
Gametes meet at fertilization Gametes meet at fertilization
Meiosis
Asexual Reproduction Asexual Reproduction
Single parent produces offspringSingle parent produces offspring
All offspring are genetically identical All offspring are genetically identical to one another and to parentto one another and to parent
Sexual ReproductionSexual Reproduction
InvolvesInvolves
MeiosisMeiosis
Gamete productionGamete production
FertilizationFertilization Produces genetic variation among Produces genetic variation among
offspringoffspring
Homologous Homologous Chromosomes Carry Chromosomes Carry
Different AllelesDifferent Alleles Cell has two of each chromosome Cell has two of each chromosome
One chromosome in each pair from One chromosome in each pair from
mother, other from fathermother, other from father
Paternal and maternal chromosomes Paternal and maternal chromosomes
carry different allelescarry different alleles
Alleles- Different forms of a Alleles- Different forms of a genegene
What is a gene?What is a gene?
Chemical factors that determine Chemical factors that determine traitstraits
Sexual Reproduction Sexual Reproduction Shuffles AllelesShuffles Alleles
Through sexual reproduction, Through sexual reproduction, offspring inherit new combinations offspring inherit new combinations of alleles, which leads to variations of alleles, which leads to variations in traitsin traits
This variation in traits is the basis This variation in traits is the basis for evolutionary changefor evolutionary change
Gamete FormationGamete Formation
Gametes are sex cells (sperm, eggs)Gametes are sex cells (sperm, eggs) Arise from germ cellsArise from germ cells
testes
ovaries
anther ovary
Chromosome NumberChromosome Number
Sum total of chromosomes in a cellSum total of chromosomes in a cell
Germ cells are diploid (2Germ cells are diploid (2nn))
Gametes are haploid (Gametes are haploid (nn))
Meiosis halves chromosome numberMeiosis halves chromosome number
Meiosis: Two DivisionsMeiosis: Two Divisions
Two consecutive nuclear divisions Two consecutive nuclear divisions Meiosis IMeiosis I
Meiosis IIMeiosis II
DNA is NOT duplicated between DNA is NOT duplicated between
divisionsdivisions
Four haploid nuclei are formedFour haploid nuclei are formed
Meiosis IMeiosis I
Each homologue in the cell pairs with its partner,
then the partners separate
Meiosis IIMeiosis II
The two sister chromatids of each The two sister chromatids of each duplicated chromosome are duplicated chromosome are separated from each otherseparated from each other
one chromosome (duplicated)
two chromosomes (unduplicated)
Stages of MeiosisStages of Meiosis
Meiosis IMeiosis I
Prophase IProphase I Metaphase IMetaphase I Anaphase IAnaphase I Telophase ITelophase I
Meiosis IIMeiosis II
Prophase IIProphase II Metaphase IIMetaphase II Anaphase IIAnaphase II Telophase IITelophase II
Meiosis I - StagesMeiosis I - Stages
Prophase I Metaphase I Anaphase I Telophase I
92
46x2 46x2 46x2 23x4
Prophase IProphase I
Each duplicated, condensed Each duplicated, condensed chromosome pairs with its homologuechromosome pairs with its homologue
Homologues swap segments !!!!!!! Homologues swap segments !!!!!!! Take note !!!!Take note !!!!
Each chromosome becomes attached Each chromosome becomes attached to microtubules of newly forming to microtubules of newly forming spindlespindle
Crossing-Over
Crossing-Over
Crossing-Over
Crossing OverCrossing Over
•Each chromosome
becomes zippered to its
homologue
•All four chromatids are
closely aligned
•Non-sister chromosomes
exchange segments
Effect of Crossing OverEffect of Crossing Over
After crossing over, each After crossing over, each
chromosome contains both maternal chromosome contains both maternal
and parental segmentsand parental segments
Creates new allele combinations in Creates new allele combinations in
offspringoffspring
Metaphase IMetaphase I
Chromosomes are pushed and pulled Chromosomes are pushed and pulled into the middle of cellinto the middle of cell
Sister chromatids of one homologue Sister chromatids of one homologue orient toward one pole, and those of orient toward one pole, and those of other homologue toward opposite pole other homologue toward opposite pole
The spindle is now fully formedThe spindle is now fully formed
Anaphase IAnaphase I
Homologous chromosomes Homologous chromosomes
segregate from each other segregate from each other
The sister chromatids of each The sister chromatids of each
chromosome remain attachedchromosome remain attached
Telophase ITelophase I
The chromosomes arrive at opposite The chromosomes arrive at opposite
polespoles
The cytoplasm dividesThe cytoplasm divides
There are now two haploid cellsThere are now two haploid cells
This completes Meiosis IThis completes Meiosis I
Meiosis II - StagesMeiosis II - Stages
Prophase II Metaphase II Anaphase II Telophase II
Prophase IIProphase II
Microtubules attach to the Microtubules attach to the kinetochores of the duplicated kinetochores of the duplicated chromosomeschromosomes
Motor proteins drive the movement Motor proteins drive the movement of chromosomes toward the of chromosomes toward the spindle’s equatorspindle’s equator
Metaphase IIMetaphase II
All of the duplicated chromosomes All of the duplicated chromosomes are lined up at the spindle are lined up at the spindle equator, midway between the equator, midway between the polespoles
Anaphase IIAnaphase II
Sister chromatids separate to Sister chromatids separate to become independent chromosomesbecome independent chromosomes
Motor proteins interact with Motor proteins interact with microtubules to move the separated microtubules to move the separated chromosomes to opposite poleschromosomes to opposite poles
Telophase IITelophase II
The chromosomes arrive at opposite The chromosomes arrive at opposite ends of the cellends of the cell
A nuclear envelope forms around A nuclear envelope forms around each set of chromosomeseach set of chromosomes
The cytoplasm dividesThe cytoplasm divides There are now four haploid cells There are now four haploid cells
Random AlignmentRandom Alignment
Either the maternal or paternal Either the maternal or paternal member of a homologous pair can member of a homologous pair can end up at either poleend up at either pole
The chromosomes in a gamete are a The chromosomes in a gamete are a mix of chromosomes from the two mix of chromosomes from the two parents parents
Possible Chromosome Possible Chromosome CombinationsCombinations
As a result of random alignment, the As a result of random alignment, the number of possible combinations of number of possible combinations of
chromosomes in a gamete is: chromosomes in a gamete is:
22nn
((nn is number of chromosome types) is number of chromosome types)
Possible Possible ChromosomChromosom
eeCombinatioCombinatio
ns ns
or
or
or
1 2 3
FertilizationFertilization
Male and female gametes unite and Male and female gametes unite and
nuclei fusenuclei fuse
Fusion of two haploid nuclei produces Fusion of two haploid nuclei produces
diploid nucleus in the zygotediploid nucleus in the zygote
Which two gametes unite is randomWhich two gametes unite is random Adds to variation among offspringAdds to variation among offspring
Factors Contributing to Factors Contributing to Variation Among Variation Among
OffspringOffspring Crossing over during prophase ICrossing over during prophase I
Random alignment of Random alignment of
chromosomes at metaphase Ichromosomes at metaphase I
Random combination of gametes Random combination of gametes
at fertilizationat fertilization
MitosisMitosis FunctionsFunctions
Asexual Asexual reproductionreproduction
Growth, repair Growth, repair Occurs in somatic Occurs in somatic
cellscells Produces clonesProduces clones
Mitosis & Meiosis Mitosis & Meiosis ComparedCompared
MeiosisMeiosis Function Function
Sexual reproductionSexual reproduction
Occurs in germ Occurs in germ cellscells
Produces variable Produces variable offspringoffspring
Prophase vs. Prophase I Prophase vs. Prophase I
Prophase (Mitosis)Prophase (Mitosis) Homologous pairs do not interact with Homologous pairs do not interact with
each othereach other
Prophase I (Meiosis) Prophase I (Meiosis) Homologous pairs become zippered Homologous pairs become zippered
together and crossing over occurstogether and crossing over occurs
Results of Mitosis and Results of Mitosis and MeiosisMeiosis
MitosisMitosis Two diploid cells producedTwo diploid cells produced
Each identical to parentEach identical to parent
MeiosisMeiosis Four haploid cells producedFour haploid cells produced
Differ from parent and one anotherDiffer from parent and one another
Pre-Natal Tests - help to determine if an at risk baby is healthy
Sex chromosomes
Human Karyotype
Sex Chromosomes
Down Syndrome (trisomy 21),
47,XY,+21.
47: the total number of chromosomes (46 is normal).
XY: the sex chromosomes (male).
+21: designates the extra chromosome as a 21.
Klinefelter’s Syndrome
47, XXY
Turner’s SyndromeTurner’s Syndrome
Only one complete XOnly one complete X The second could also be incompleteThe second could also be incomplete In almost all cases, unable to repro. In almost all cases, unable to repro.
Or menstruate Or menstruate
HermaphroditeHermaphrodite
XX/XY or XOXX/XY or XO 350-400 Known cases350-400 Known cases
Gene Therapy - an absent or faulty gene is replaced by a working gene
Has not been very successful