Ch 13 Sexual Life Cycles and Meiosis. Living organisms Have ability to reproduce Heredity...
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Transcript of Ch 13 Sexual Life Cycles and Meiosis. Living organisms Have ability to reproduce Heredity...
Ch 13 Sexual Life Cycles and Meiosis
• Living organismsHave ability to reproduce
• HeredityTransmission of traits from one generation to the next
• Variation• Offspring often differ in appearance from parents and
siblings • Environmental and genetic influences
• GeneticsScientific study of heredity and variation
Reproduction and the Transmission of Traits
Progeny (or offspring)-Inherit chromosomes from parents
-DNA in chromosomes encode the genes thatspecify characteristics
For exampleeye color, blood type, predisposition to disease
What are the mechanisms by which chromosomes are passed onto (eukaryotic) offspring?
Asexual reproduction
Sexual reproduction
LE 13-2
Parent
0.5 mm
Bud
Asexual reproductionBud forms by mitosis of parent cellsBud genetically identical to parent
Sexual Reproduction
1. Meiosis: formation of haploid gametes (eggs, sperm) in parents
2. Fertilization: fusion of gametes from opposite parents--> diploid zygote-->mitotic growth-->embryo-->adult
LE 13-5
Key
Haploid (n)
Diploid (2n)
Haploid gametes (n = 23)
Ovum (n)
Spermcell (n)
TestisOvary
Mitosis anddevelopment
Multicellular diploidadults (2n = 46)
FERTILIZATIONMEIOSIS
Diploidzygote(2n = 46)
HumanSexualReproduction
Offspringgenetically uniquefrom parents
How many chromosomes are inherited by human zygotes?
46 chromosomes
or
2n= 46
n= the number of chromosomes in a set
23 from mother, maternal chromosomes23 from father, paternal “
LE 13-3
5 µmHuman Karyotype
Stained metaphasechromosomesfrom humansomatic cell
Why stain metaphase
chromosomes?
Compact &easier to see com-pared to interphase
LE 13-3
5 µmPair of homologouschromosomes
Sisterchromatids
Centromere
Can you tell the difference between a human male and female by the karyotype?
Humans have 22 pairs of autosomes (non-sex chromosomes) 1 pair of sex chromosomes
Female sex ch.: XX Male sex ch.: XY
LE 13-3
5 µmHuman Karyotype
Male or female?
If somatic cells have two sets of chromosomes (diploid), how do gametes end up with only one set (haploid)?
Diploid precursors to the egg and sperm undergo meiosis in the testis and ovary.
LE 13-7
Homologous pairof chromosomesin diploid parent cell
Interphase
Homologous pair of replicated chromosomes
Chromosomesreplicate
Meiosis I
Diploid cell withreplicatedchromosomes
Sisterchromatids
Meiosis II
Homologouschromosomesseparate
Sister chromatidsseparate
Haploid cells withreplicated chromosomes
Haploid cells with unreplicated chromosomes
Overview of meiosis
aka tetrad
Diploid
Haploid
LE 13-4
Key
Maternal set ofchromosomes (n = 3)
2n = 6
Paternal set ofchromosomes (n = 3)
Two sister chromatidsof one replicatedchromosomes
Two nonsister chromatids in a homologous pair
Pair of homologouschromosomes(one from each set)
Centromere
LE 13-8ab
Sisterchromatids
Chiasmata
Spindle
Centromere(with kinetochore)
Metaphaseplate
Homologouschromosomesseparate
Sister chromatidsremain attached
Microtubuleattached tokinetochore
Tetrad
MEIOSIS I: Separates homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I
Homologous chromosomes (red and blue) pair andexchange segmentsHomologous recombination (crossing-over)
Pairs of homologouschromosomes split up
Tetrads line up
LE 13-8b
Cleavagefurrow
MEIOSIS II: Separates sister chromatids
PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I AND
CYTOKINESISTELOPHASE II AND
CYTOKINESIS
Sister chromatidsseparate
Haploid daughter cellsforming
Two haploid cellsform; chromosomesare still double
During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes
LE 13-9
Prophase
Duplicated chromosome(two sister chromatids)
Chromosomereplication
2n = 6
Parent cell(before chromosome replication)
Chromosomereplication
MITOSIS MEIOSIS
Chiasma (site ofcrossing over) MEIOSIS I
Prophase I
Tetrad formed bysynapsis of homologouschromosomes
Tetradspositioned at themetaphase plate
Metaphase IChromosomes positioned at themetaphase plate
Metaphase
AnaphaseTelophaseCytokinesis
Homologuesseparateduringanaphase I;sisterchromatidsremain together
Sister chromatidsseparate duringanaphase
Daughtercells of
meiosis I
Haploidn = 3
Anaphase ITelophase I
MEIOSIS II
Daughter cellsof mitosis
2n2n
n
Sister chromatids separate during anaphase II
n n n
Daughter cells of meiosis II
Mitosis producestwo genetically identical diploid cells
Meiosis producesfour genetically distinct haploid cells
Mechanisms of Genetic Variation Among OffspringCaused by Sexual Reproduction
1. Crossing over (homologous recombination)
(Prophase I)
2. Independent assortment of chromosomes
(Metaphase I & II)
3. Random fertilization (post-meiosis)
LE 13-11
Prophase Iof meiosis
Tetrad
Nonsisterchromatids
Chiasma,site of crossingover
Recombinantchromosomes
Metaphase I
Metaphase II
Daughtercells
Recombination
Chiasmata, pl
LE 13-10
Key
Maternal set ofchromosomes
Paternal set ofchromosomes
Possibility 1 Possibility 2
Combination 2Combination 1 Combination 3 Combination 4
Daughtercells
Metaphase II
Metaphase ITwo equally probable
arrangements ofchromosomes at
Independent Assortment
Random Fertilization
• Any sperm can fuse with any ovum (unfertilized egg)
• a (human) zygote has about 64 trillion diploid combinations
• Each zygote has unique genetic identity
I think they were talking about us. I hope they had it right!
If not maybe we can answer questions.
See meiosis animation
What is missing?