Biology Meiosis. Remember from Chapter 1: CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS...
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Transcript of Biology Meiosis. Remember from Chapter 1: CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS...
BiologyBiology
Meiosis
Remember from Chapter 1:CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS __________
REPRODUCE
Remember from Chapter 7, there are basically 2 types of cells__________ and ____________
EUKARYOTICPROKARYOTIC
Now let’s review Ch 10..........
Mitotic Cell Division• Mitosis makes two identical
daughter cells from one Parent cell• Bacteria and other prokaryotes
may use mitosis to reproduce – called Binary Fission
• This is asexual reproduction
ASEXUAL REPRODUCTION
Bacteria reproduce using
BINARY FISSION
This is mitosis!
Budding is used by plants and some animals to reproduce asexually (mitosis)
Regeneration is another way some animals reproduce asexually (mitosis)
Hydra
Planaria
MITOSIS
Produces cells that are __________ copies of parent cell
identical
Major Events in MitosisMajor Events in Mitosis
• Chromosome number must be maintained in animals.
• Many plants have more than two copies of each chromosome.
• Mitosis and meiosis are types of nuclear division that make different types of cells.
• Mitosis makes more diploid cells.
MITOSIS-in conclusion
•Makes ___ cells genetically _________ to parent cell & to each other
•Makes _________ cells•Makes __________•Used by organisms to:
increase size of organism, repair injuries, and replace worn out cells
2identical
2n (diploid) SOMATIC (body)
ADVANTAGES OF ASEXUAL REPRODUCTION
Can make offspring faster
Don’t need a partner
ADVANTAGES OF ASEXUAL REPRODUCTION
Works great for making new skin cells, blood cells, and any of the other body cells that need to be replaced
Our body cells are called Somatic cells (repeat word)
DISVANTAGES OF ASEXUAL REPRODUCTION
ALL ALIKENo genetic diversity within a population
One disease can wipe out whole population
Question….if not asexual, then how can
we reproduce?
Sexual Reproduction
Sexual reproduction is when two gametes (sex cells) fuse together to make a zygote.
SEXUAL REPRODUCTION
In humans, (and in many other organisms), sexual reproduction combines the genetic material from the gametes of 2 parents (sperm & egg) into a zygote
-develops into offspring that are genetically __________ from parents
DIFFERENT
• Let’s review sexual reproduction• In sexual reproduction, there are two
parents.• Each parent has a gamete, or sex cell to
donate to the offspring.• Each gamete has one set of chromosomes. • The two gametes come together
(fertilization) to form one new cell called a Zygote.
• This Zygote will grow and divide to become a unique organism.
ADVANTAGES OF SEXUAL REPRODUCTION
Allows for variation in population
Individuals can be different
Provides foundation for EVOLUTION
Allow species adapt to changes intheir environment
EGG + SPERM
If egg and sperm cells had the same number of chromosomes as other body cells . . . baby would have too many chromosomes!
MEIOSIS is the way we can avoid this problem.
Meisosis makes cells with half the number of chromosomesfor sexual reproduction
• Germ cells develop into_ gametes.– Germ cells are located in the ovaries and testes of
humans and other animals.– Gametes are sex cells:__________.– Gametes have DNA that is passed to the offspring.
sex cells
(sperm) (egg)
Sex Cells (also called germ cells)
egg and sperm
• Haploid (n) cells have one copy of every chromosome.(Remember diploid cells have two copies)–Gametes are haploid.–Human gametes have 22 autosomes and 1 sex chromosome.
Haploid cells develop into mature gametes.
• Gametogenesis is the production of gametes.• Gametogenesis differs between females and
males.
–Sperm become streamlined and motile.
–Sperm primarily contribute DNA to an embryo.
Haploid cells develop into mature gametes.
• Gametogenesis differs between females and males.
–Eggs contribute DNA, cytoplasm, and organelles to an embryo.
–During meiosis, the egg gets most of the contents; the other cells form polar bodies.
KEY CONCEPT Gametes have half the number of chromosomes that body cells have.
DIPLOID & HAPLOIDMost cells have 2 copies of each
chromosome = ______________(one from mom; one from dad)
All BODY (___________) cells are diploid
DIPLOID 2n
HOMOLOGOUSCHROMOSOMES
SOMATIC
HOMOLOGOUS Chromosomes• SAME SIZE• SAME SHAPE• CARRY GENES for the
SAME TRAITS• BUT ______________! (Don’t have to have
the SAME CHOICES)
NOT IDENTICAL
DIPLOID & HAPLOIDSome cells have only one copy of each
chromosome = _____________Fertilization between egg and sperm
occurs in sexual reproduction.
All gametes (sperm and egg) cells are haploid
HAPLOID 1n
SO……what is a chromosome?
• main organelle involved in the Cell Cycle
• Found in the nucleus
• Contains genetic material (DNA)
• Has 2 major parts-a centromere and sister chromatids
• Your body cells have 23 pairs of chromosomes.– Homologous pairs
of chromosomes have the same structure.
– For each homologous pair, one chromosome comes from each parent.
There are two types of Chromosomes.
• Chromosome pairs 1-22 are autosomes.
• Sex chromosomes, X and Y, determine gender in mammals.
There are two types of Chromosomes.
• Humans have 46 chromosomes (23 pair)• Cats have 38 chromosomes (19 pair)• Chickens have 78 chromosomes (39 pair)• Horses have 64 chromosomes (32 Pair)• Potatoes have 48 chromosomes (24 pair)• Goldfish have100 chromosomes (50 pair)• Fruit fly has 8 (4 pair)• Corn has 20 (10 pair)• Peas have 14 (7 pair)• Mosquitoes have 6 chromosomes (3 pair)• Mice have 40 chromosomes (20 pair)• Elephants have 56 chromosomes (28)
• The zygote of humans have 23 pairs of chromosomes (or 46 individual chromosomes)
• 23 chromosomes come from each parent
• 23 + 23 = 46• Humans have 46 chromosomes
So Again……
The process of Meiosis- The
Formation of Sex Cells
• Meiosis makes haploid cells from diploid cells.
–Meiosis occurs in sex cells. –Meiosis produces gametes.
I. Introduction to Meiosis
A. Purpose - to make sex cells for reproduction.
B. Why can’t mitosis do this?
Remember….mitosis would make too many chromosomes.
MEIOSIS•Makes ____ cells
genetically different from parent cell & from each other
•Makes _____ cells•Makes ______________
•Used for ____________
4
1n Germ cellsOR Gametes (sperm & eggs)
sexual reproduction
WHAT MAKES MEIOSIS DIFFERENT ?
Crossing Over, Segregation, and Independent Assortment
ALL are ways MEIOSIS results in
=______________________________
So daughter cells are ______________from parents and from each other
different
GENETIC RECOMBINATION
WHAT MAKES MEIOSIS DIFFERENT ?
1.Homologous chromosomes pair up during ________________
= ______________SYNAPSIS
This group of FOUR (4)chromatids is called a_________________TETRAD
PROPHASE I
WHAT MAKES MEIOSIS DIFFERENT?
1. Exchange of DNA betweenhomologous pairs = _____________during PROPHASE I
CROSSING OVER
Separates gene choices and Allows shuffling of genetic material
CROSSING
OVER
• Allows for_________________in different combinations
• After crossing over, chromatid arms are________________ anymore
rearranging of DNA
NOT IDENTICAL
WHAT MAKES MEIOSIS DIFFERENT ?
Separation during ANAPHASE I-chromosome pairs separate
SEGREGATION & INDEPENDENT ASSORTMENT
SEGREGATION & CROSSING OVERtogether make even more
combinations
INDEPENDENT ASSORTMENT
INDEPENDENT ASSORTMENT
at ANAPHASE I
Lots of different combinations are possible!
This is why you don’t look exactly like your brothers and sisters even though you share the same parents!
SO WHAT MAKES MEIOSIS DIFFERENT ?
1. SYNAPSIS & CROSSING OVER (PROPHASE I)
2. SEGREGATION & INDEPENDENT ASSORTMENTin Anaphase I create genetic recombination
3. Skip INTERPHASE II (NO S) CELL DIVIDES TWICE, BUT… ONLY COPIES DNA ONCE
WHAT MAKES MEIOSIS DIFFERENT ?
3. Skip INTERPHASE II (No S) CELL DIVIDES TWICE, BUT … ONLY COPIES ITS DNA ONCE
G1 G2S P M A T C
G1
MITOSIS:
MEIOSIS:
S G2 P M A T CP M A T C
( I )
( II )
Workings of Meiosis
A. Meiosis is - the formation of sex cells (eggs and sperm)
1. Gametes - another name for sex cells.
A. Gametes have haploid chromosome number
B. Meiosis is the making of eggs and sperm with half the number of chromosomes as the parent cell.
1. Female egg = 23
2. Male sperm = 23
C. Two Main Stages of Meiosis
1. Meiosis I a. Prophase I b. Metaphase I c. Anaphase I d. Telophase I
2. Meiosis II
a. Prophase II
b. Metaphase II
c. Anaphase II
d. Telophase II
D. There is only one interphase
Cells go through two rounds of division in meiosis.
• Meiosis reduces chromosome number and creates genetic diversity.
• Meiosis I and meiosis II each have four phases, similar to those in mitosis.
homologous chromosomes
sisterchromatid
s
sisterchromatid
s
– Pairs of homologous chromosomes separate inmeiosis I.
– Homologous chromosomes are similar but not identical.
– Sister chromatids divide in meiosis II.– Sister chromatids are copies of the same
chromosome.
• Meiosis I occurs after DNA has been replicated.• Meiosis I divides homologous
chromosomes in four phases.
• Meiosis II divides sister chromatids in four phases.
• DNA is not replicated between meiosis I andmeiosis II.
Meiosis I
A. Interphase
1. Replication of chromosomes occurs.
2. This is the only interphase.
B. Prophase I
1. Chromatids appear
2. Centrioles split.
3. Centrioles move to the opposite poles.
4. Spindle fibers appear
5. Nucleolus disappears
6. Nuclear membrane disappears
7. Tetrads form - two pairs of homologous chromosomes joining together.
8. Crossing-over occurs here - genes are exchanged between homologous chromsomes.
a. Creates variation in new offspring
C. Metaphase I
1. Tetrads line up at the equator.
D. Anaphase I
1. Tetrads separate.
2. Chromatids are pulled to the opposite poles.
E. Telophase I
1. Chromatids still visible.
2. Nucleolus and Nuclear Membrane reforms.
3. Centrioles replicate
4. Two new cells.
IV. Meiosis IIA. No interphase begins this
phase. 1. 2 cells with the haploid
chromosome number begin this stage.
2. Meiosis II will always have two cells in each phase.
B. Prophase II 1. Nuclear membrane and
nucleolus disappear. 2. Centrioles split 3. Centrioles move to the
poles.
4. Spindle fibers form.
5. Chromatids are visible and attach to spindle fibers.
C. Metaphase II
1. Chromatids line up on the equator.
D. Anaphase II
1. Centromeres separate.
2. Chromotids are pulled to opposite poles.
E. Telophase II
1. Centrioles replicate
2. Nuclear membrane and nucleolus reappear.
3. Spindle fibers disappear.
4. 4 new cells are formed
a. Only have half the number of chromosomes as the parent cell.
b. Males - all 4 remain alive and viable.
c. Females – one egg grows rest (polar bodies) die off.
V. Meiosis-Mitosis Comparison
A. Mitosis
1. 4 phases
2. Produces 2 diploid cells
3. Daughter cells identical to parent
B. Meiosis
1. 8 phases
2. 4 haploid cells produced
3. Daughter cells not identical to parent
4. Contain tetrads and crossing-over.
• Meiosis differs from mitosis in significant ways.
– Meiosis has two cell divisions while mitosis has one.
– In mitosis, homologous chromosomes never pair up.
– Meiosis results in haploid cells; mitosis results in diploid cells.
Meiosis I
Section 11-4
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Figure 11-15 Meiosis
Meiosis I
Meiosis I
Section 11-4
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Figure 11-15 Meiosis
Meiosis I
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
That’s All For Now Folks!