State StandardsGenetics State Standards 10.4 In sexually reproducing organism, each offspring contains a mix of characteristics inherited from both parents.Genetics CAPT Strands D 34. Describe, in general terms, how the genetic information of organisms can be altered to make them produce new materials. D 35. Explain the risks and benefits of altering the genetic composition and cell products of existing organisms. D 36. Explain how meiosis contributes to the genetic variability of organisms.
Objectives Understand that most organisms have two genes for each trait. Illustrate how meiosis contributes to genetic variability. Create a visual representation of the stages of meiosis.
Meiosis The process to make cells with half the number of chromosomes for sexual reproduction Occurs in our germ cells that produce gametes Sperm & egg Results in four cells genetically different from parent cell and from each other Haploid (n) cells
Why Do We Need Meiosis? It is the fundamental basis of sexual reproduction Two haploid (n) gametes are brought together through fertilization to form a diploid (2n) zygote If egg and sperm had the same number of chromosomes as other body cells then the offspring would have too many chromosomes.
Meiosis Meiosis must reduce the chromosome number by half (n) Fertilization then restores the 2n number from mom from dad child too much! meiosis reduces genetic content The right number!
Meiosis-Replication Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere
Meiosis Gene Z Homologous Sister chromosomes Chromatids (same genes, (same genes,different alleles) same alleles) Homologous chromosomes are the same size & shape Carry genes for the same trait but are not identical!
CheckpointMeiosis results in ____. 1. 4 identical cells 2. 4 genetically different cells 3. 2 genetically different cells 4. 2 identical cells
CheckpointHomologous chromosomes are _____. 1. Same in size 2. Same in shape 3. Carry genes for the same trait 4. All of the above
CheckpointWhy do we need meiosis?A: To reduce the chromosome number in gametes, otherwise offspring would have too many chromosomes
Meiosis Sister chromatids separate Homologous chromosomes separate Meiosis I Meiosis IIDiploid Diploid Haploid
Meiosis I SpindleNucleus fibers Nuclear envelopeEarly Prophase I Telophase I(Chromosome Late Prophase I Metaphase I Anaphase I (haploid)# doubled)
Prophase I : Crossing-Over Synapsis – the pairing of homologous chromosomes Group of 4 chromatids Homologous chromosomes Join to form a (each with sister chromatids) TETRAD
Prophase I : Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces genetic recombination in the offspring
Prophase I : Crossing-Over Homologous chromosomes during crossing-over
Metaphase I Homologous pairs of chromosomes align along the equator of the cell
Anaphase I Homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached at their centromeres.
Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.
Meiosis II Only one of the homologous pairGene Z of chromosome is present in the cell. Sister chromatids carry identical genetic information.Meiosis II produces gametes with one copy of eachchromosome and thus one copy of each gene.
Meiosis IIProphase II Metaphase II Anaphase II Telophase II 4 different haploid cells
Prophase II Nuclear envelope fragments. Spindle forms.
Metaphase II Chromosomes align along equator of cell.
Anaphase II Pole Sister chromatids separate and move to opposite poles. Equator 26
Telophase II Nuclear envelope assembles. Chromosomes unwind. Spindle disappears. Cytokinesis divides cell into two.
Results of Meiosis Gametes (egg & sperm) form Four haploid cells (n) with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome
CheckpointWhich best describes crossing-over? 1. Pieces of genes are exchanged 2. Allow genetic variation 3. Occurs in Prophase I 4. All of the above
CheckpointDuring anaphase I in meiosis what is pulled apart? 1. Centromere 2. Homologous chromosomes 3. Sister chromatids 4. Spindle fibers
CheckpointWhich best describes a haploid cell? 1. n 2. Half the genetic information 3. Gametes 4. All of the above
Spermatogenesis Occurs in the testes Two divisions produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day
Oogenesis Occurs in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 days
Oogenesis Polar body a (haploid) X a Polar Bodies X a (haploid) a X X Mitosis Meiosis I Meiosis II A XOogonium A(diploid) Primary X oocyte A X (diploid) Ovum Mature Secondary A Egg (haploid) oocyte X (haploid) Second polar body (haploid)
CheckpointHow many chromosomes would a sperm or egg contain if either one resulted from the process of mitosis?A: 46 Chromosomes
CheckpointWhy is the sperm so small compared to the egg?A: The egg has all the starting nutrients, organelles and building blocks. The sperm only provides DNA. That is why oogenesis only produces one ‘good’ egg.
Mitosis Meiosis Number of 2 1 divisions Number of 2 4daughter cells Genetically Yes No identical?Chromosome # 46 23 Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction
MeiosisThe process to make cells with ___________ thenumber of chromosomes for sexual reproductionOccurs in our germ cells that produce gametes ___________ & ______________Results in ____________ cells genetically differentfrom parent cell and from each otherHaploid (____) cells
Why Do We Need Meiosis?It is the fundamental basis of sexual reproductionTwo ____________ (n) gametes are brought togetherthrough fertilization to form a _______________(2n) _______________If egg and sperm had the same number ofchromosomes as other body cells then the offspringwould have too many chromosomes.
Meiosis must ____________ the chromosome number by____________ (n)_____________________ then restores the 2n number from mom from dad child too much! meiosis ____________ genetic content The right number!
Meiosis-ReplicationReplication is the process ofduplicating a______________________Occurs prior to divisionReplicated copies are calledsister chromatidsHeld together at__________________
Gene Sister Homologous Chromatids chromosomes (same ________, (same _________, same _________)different ________)Homologous chromosomes are the same ________ & ___________Carry genes for the same trait but are _______ identical!
CHECKPOINT √ Meiosis results in ____.1. 4 identical cells 2. 4 genetically different cells3. 2 genetically different cells 4. 2 identical cells Homologous chromosomes are _____. 1. Same in size 2. Same in shape 3. Carry genes for the same trait 4. All of the above Why do we need meiosis?
Sister chromatids separate Homologous chromosomes separate Meiosis I Meiosis II______________ ______________ ______________
Early prophase I Late prophase I Homologous pair. Chromosomes condense. Crossing over occurs. Spindle forms. Nuclear envelope fragments.
Prophase I : Crossing-Over_____________ – the pairing of homologouschromosomes Group of 4 __________________ Homologous chromosomes Join to form a (each with sister chromatids) ________________
Homologouschromosomes in a tetrad____________________each otherPieces of chromosomes orgenes are____________________Produces geneticrecombination in the____________________
Metaphase I Anaphase I Telophase I________________ Homologous Nuclear envelopes________________ chromosomes reassemble.of chromosomes _______________align along the Spindle disappears.equator of the cell Sister chromatids Cytokinesis divides remain attached at cell into ________. the _____________
Meiosis II Only _______ of the homologous pair of chromosome is present in the cell.Gene Z Sister chromatids carry _________________ genetic information. Meiosis II produces _______________ with one copy of each chromosome and thus one copy of each _________.
Prophase II Metaphase II Anaphase IINuclear envelope Chromosomes ________________fragments. align along ________________ ________________ separate and moveSpindle forms. of cell. to opposite poles.
Results of Meiosis _____________(egg & sperm) form Four haploid cells (___) with one copy of each chromosome One ________ of each gene ________________ combinations of alleles for different genes along the chromosome
CHECKPOINT √ Which best describes crossing-over?1. Pieces of genes are exchanged 2. Allow genetic variation3. Occurs in Prophase I 4. All of the above During anaphase what is pulled apart? 1. Centromere 2. Homologous chromosomes 3. Sister chromatids 4. Spindle fibers Which best describes a haploid cell?1. n 2. Half the genetic information3. Gametes 4. All of the above
SpermatogenesisOccurs in the ___________Two divisions produce 4__________________Spermatids mature into__________________Men produce about250,000,000 sperm per day
OogenesisOccurs in the _________________Two divisions produce: _______ __________ bodies that die because of unequal division of cytoplasm _____ egg- Immature egg called _____________Starting at puberty, one oocyte matures into an ovum(egg) every 28 days
CHECKPOINT √How many chromosomes would a sperm or egg contain if either one resulted from the process of mitosis? Oogenesis results in______. 1. 4 polar bodies 2. 3 polar bodies 3. 1 ovum 4. Both 2 & 3 Why is the sperm so small compared to the egg?
Mitosis MeiosisNumber of divisionsNumber of daughter cells Genetically identical? Chromosome # Where When Role
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