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AP BiologyModified from: Kim Foglia,
Explore Biology
Chapter 13.
Meiosis &Sexual Reproduction
AP Biology
How about the rest of us? What if a complex multicellular organism
(like us) wants to reproduce? joining of egg + sperm
Do we make egg & sperm by mitosis?
46 46+ 92
egg sperm zygote
AP Biology
Human female karyotype
AP Biology
Human male karyotype
AP Biology
How do we make sperm & eggs? reduce 46 chromosomes 23 chromosomes
half the number of chromosomes
23
2346
egg
sperm
46
meiosis 46
fertilization
23
23
AP Biology
Meiosis: production of gametes
Alternating processes,alternating stages chromosome number
must be reduced diploid haploid 2n n
humans: 46 23 meiosis reduces
chromosome number fertilization restores
chromosome number haploid diploid n 2n
AP Biology
Homologous chromosomes Paired chromosomes
both chromosomes of a pair carry genes control same inherited characters homologous = same information
diploid2n
homologouschromosomes
double strandedhomologous chromosomes
AP Biology
2nd division of meiosis separates sister chromatids
1st division of meiosis separates homologous pairs
Double divisionof meiosis
DNA replication
AP Biology
Steps of meiosis Meiosis 1
interphase prophase 1 metaphase 1 anaphase 1 telophase 1
Meiosis 2 prophase 2 metaphase 2 anaphase 2 telophase 2
2nd division of meiosis separates sister chromatids
(1n 1n)
* just like mitosis *
1st division of meiosis separates homologous pairs
(2n 1n)
AP Biology
AP Biology
AP Biology
Crossing over During Prophase 1
homologous pairs swappieces of chromosome
sister chromatids intertwine crossing over
tetrad
synapsis
AP Biology
Crossing over 3 steps
cross over breakage of DNA re-fusing of DNA
New combinations of traits
What are theadvantages of
sexual reproduction?
AP Biology
Genetic variation Meiosis & crossing over introduce
great genetic variation to population drives evolution
AP Biology
The value of meiosis Meiosis introduces genetic variation
gametes of offspring do not have same genes as gametes from parents
genetic recombination random assortment in humans produces 223
(8,388,608) different combinations
from Mom from Dadnew gametes
made by offspring
AP Biology
And more variation… Crossing over
creates completely new combinations of traits in next generation
AP Biology
Random fertilization Any 2 parents will produce a zygote
with over 70 trillion (223 x 223) diploid combinations
AP Biology
Sources of genetic variability Genetic variability in sexual reproduction
independent assortment homologous chromosomes in Meiosis 1
crossing over between homologous chromosomes in
prophase 1 random fertilization
random ovum fertilized by a random sperm
metaphase1
AP Biology
Sexual reproduction creates variabilitySexual reproduction allows us to maintain both genetic similarity & differences.
Martin & Charlie Sheen, Emilio Estevez
Michael & KirkDouglas
Baldwin brothers
AP Biology
Cell A has 4 chromosomes and Cell D has 2 chromosomes. What process created Cell D?
1. Mitosis
2. Asexual Reproduction
3. Fusion
4. Meiosis Cell A Cel
l B Cell C Cel
l D1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 2410
AP Biology
Cell A is considered _______ while Cell D is considered ________.
Cell A
Cell B Cel
l C Cell D
1 2 3 4
0% 0%0%0%
1. Haploid; Diploid
2. Tetrad; Diploid
3. Diploid; Haploid
4. Homologous; Haploid
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24
10
AP Biology
Cell A is considered _______ while Cell D is considered ________.
A. somatic cell; gamete
B. gamete; somatic cell
C. stem cell; somatic cell
D. stem cell; gamete
somatic c
ell; gamete
gamete; s
omatic cell
stem ce
ll; so
matic cell
stem ce
ll; gamete
0% 0%0%0%
30
AP Biology
How can we best describe the diagram below?
1 2 3 4
0% 0%0%0%1. Two sister chromatids2. Homologous chromosomes3. One replicated chromosome4. Haploid chromsomes
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 2410
AP Biology
What process is best demonstrated by the diagram below?
1 2 3 4
0% 0%0%0%
1. Anaphase I2. Segregation of alleles3. Crossing over 4. Independent assortment
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 2410
AP Biology
Which of the following leads to genetic variation during meiosis?
1 2 3 4 5
0% 0% 0%0%0%
A.Crossing Over
B.DNA replication
C.Independent assortment
D.Mitotic spindle formation1. All of the above (A, B, C, D)2. A & B3. A & D4. A, B, & D5. A & C
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 2410
AP Biology
Mitosis vs. Meiosis Mitosis
1 division daughter cells
genetically identical to parent cell
produces 2 cells 2n 2n produces cells for
growth & repair no crossing over
Meiosis 2 divisions daughter cells
genetically different from parent
produces 4 cells 2n 1n produces gametes
crossing over
AP Biology
Mitosis vs. Meiosis
AP Biology
Changes in Chromosomes Number Euploidy = correct # of chromosomes Aneuploidy = a change in
chromosomes number due to non-disjunction during meiosis
Monosomy- only 1 copy of an individual chromosome
Trisomy- 3 copies of an individual chromosome
AP Biology
Non-disjuction Primary nondisjuction = Meiosis I
Secondary nondisjuction = Meiosis II
AP Biology
Trisomy 21 : Down Syndrome Delayed mental and social skills Decreased muscle tone at birth Asymmetrical or odd-shaped skull Small skull Small mouth with protruding tongue Broad short hands Increased risk of developing Leukemia and Alzheimer’s later in life
AP Biology
AP Biology
Trisomy 18 : Edward’s Syndrome Most children die in the first year of life, some have lived 10
years Growth deficiency Feeding difficulties Breathing difficulties Developmental delays Mental Retardation Overlapped, flexed fingers Webbing of the second and third toes Clubfeet Structural heart defects at birth
AP Biology
Trisomy 13 : Patau Syndrome Mental retardation, severe Seizures Small head Scalp defects Cleft lip and/or palate Eyes close set (hypotelorism) –may fuse Extra digits (polydactyl) Hernias Undescended testicle Children die in the first year of life
AP Biology
Karyotype A visual display of the chromosomes arranged by
size, shape, and banding pattern Used to identify aneuploid conditions
AP Biology
Procedure: Amniocentesis and Karyotyping
AP Biology
Karyotyping
AP Biology
Changes in Sex Chromosome # Turners Syndrome (XO) – missing Barr Body Kleinfelter’s Syndrome (XXY) Swyer Syndrome (XY female) La Chapelle Syndrome (XX male) Poly-X Females (XXX, XXXX) Jacob’s Syndrome (XYY males)
-SRY gene (located on short arm of Y chromosome)
-hormone= testis-determining factor
-Barr Body – Inactive X chromosome (XX)
AP Biology
Chromosomal Mutations
AP Biology
Deletion Syndromes Williams Syndrome (deletion of a piece
of chromosome 7) Cri du chat (cat’s cry) (deletion of a
piece of chromosome 5)
AP Biology
Translocation Syndromes Alagille syndrome – Chromosomes 2
and 20 exchange segments Cancers
Chronic myelogenous leukemia (2 and 9)
Burkitt lymphoma (8 and 14)
AP Biology
Any Questions??
What are theDISadvantages of
sexual reproduction?