grade 8 module 5
DESCRIPTION
scienceTRANSCRIPT
5 MODULES IN 4TH QUARTER
MODULE 1: BIODIVERSITY
MODULE 2: INTERACTIONS
MODULE 3: THE DIGESTIVE SYSTEM
MODULE 4: NUTRITION & WELLNESS
MODULE 5: CELLULAR REPRODUCTION & GENETICS
BIOLOGY Module 5
STORY LINE
• GRADE 3Pupils learned that living things reproduce and certain traits are passed on to their offspring
GRADE 4• Pupils learned
that humans, animals, and plants go through life cycles.
• Some inherited traits may be affected by the environment at certain stages in their life cycles.
STORY LINE
• GRADE 5• Pupils learned how
flowering plants and some non-flowering plants reproduce.
• They were also introduced to the sexual and asexual modes of reproduction.
GRADE 6• Pupils learned how non-
flowering plants (spore-bearing and cone-bearing plants, ferns, and mosses) reproduce.
STORY LINE• GRADE 7• After learning how
flowering and non-flowering plants reproduce, Grade 7 students learned that asexual reproduction results in genetically identical offspring whereas sexual reproduction gives rise to variation
GRADE 8 Students will learn the
process of cell division by mitosis and meiosis.
They will understand that meiosis is an early step in sexual reproduction that leads to variation.
Suggested Time allotment: 4 to 5 hours
KEY QUESTIONS:
•What are the different types of cell division?
•How are traits passed on to the next generation?
TOPICS INCLUDED:Review on the Cell Function Review on the Location of Chromosomes in
the CELLCell Cycle: Interphase (G1, S phase, G2)
Mitotic Phase Meiotic Phase
Nondisjunction (Chromosomal Aberrations)CLASSICAL GENETICS
-Mendelian Genetics-Non-Mendelian Pattern of Inheritance
Sex-Linked TraitsSex Chromosomes and Sex Determination
Cell Cycle Makes up the entire life of the cell
• Consists of 2 major stages:– Interphase – Mitotic Phase
• Interphase G0 -zero growth (Gap O) G1- initial growth(Gap 1)• S - synthesis• G2 - growth 2 (Gap2)
Cell Cycle Part 1:Interphase = normal phase of the cell.
Chromosomes NOT visible. – DNA in form called chromatin
▪ Looks like spaghetti The nuclear
envelope/membrane present
DNA replication Cell growth
Mitosis - Review
Cell Cycle Part 2: Cell Division
• Also known as Mitotic Phase
• Where Mitosis and Cytokinesis occur
• A continuous process divided into 4 main stages
• Daughter Cells – 2 new cells produced by cell division.
Mitosis = division of 1 diploid nucleus into 2 identical diploid nuclei
• All somatic/body cells undergo mitosis for growth, repair or replacement of old cells
• Diploid cell (2n). – cells with 2 sets of chromosomes.
1 set-comes from male parent
1 set-comes from female parent
Mitosis in an actual cell
Prophase – 1st phase of mitosis.
• Chromatin materials becomes thicker and shorter because of repeated coiling• Chromosomes are now visible • Centrioles form spindle• Nuclear envelope/membrane and nucleoli breaks apart.• The longest time to occur.
Metaphase – 2nd phase
Chromosomes meet and align in middle or equator. Spindle fibers attach to centromere Nuclear envelope/membrane is gone.
Anaphase – 3rd phase
Centromere splits at the center of the chromosomes. Chromatids move away from each other. Spindles pull chromatids apart The nuclear envelope/membrane still absent
Telophase – 4th phase
• Chromosomes begin to disappear.
• Spindle fibers disappear• Two new nuclear
envelopes/membranes begin to form
• Nucleoli reappear.• “reverse prophase”
Cytokinesis
• Division of the cell membrane and cytoplasm.
• Forms two new Daughter cells
Mitosis - Overview
Interphase
Early Prophase
Late Prophase
Metaphase
Early Anaphase
Telophase - Cytokinesis
Telophase - Cytokinesis
Check for understanding!
• 11. Why are the onion root tip and the whitefish blastula useful tissues for the study of cell division? . Why are the onion root tip and the whitefish blastultissues for the study of cell division?
• These two tissues were actively dividing, so we could find cells under going mitosis at different phases.
• 2. Distinguish between mitosis and cytokinesis.
Mitosis is the division of the nucleus (nuclear division) produces 2 identical nuclei. Cytokinesis is the division of the cytoplasm – produces 2 cells.
• 3. If a cell has 16 chromosomes when it is in G1, how many chromosomes will there be in each daughter cell following a mitotic cell division?
• 16
• 4. What are the genetic consequences of mitotic cell division for the resulting daughter cells?
Every cell is genetically identical to each other. Produces 2 identical nuclei, each with the same number and types of chromsomes as the parent cell.
• 6. How do plant and animal cells differ in the execution of cytokinesis? Why don’t plant cells undergo cytokinesis in the same manner as animal cells?
• During cytokinesis plant cells form a cell plate while animal cells form a cleavage furrow.
• Plant cell has a rigid cell wall
Moving On…
• 7. List several important values or attributes that mitotic cell division provides to multicellular life. In other words, in what ways is mitotic cell division useful for life?
• 8. List the 4 stages of the cell cycle and describe the primary cellular activity in each stage.
Cell Division
• Reproduction– Equal distribution of genetic
material to two daughter cells
• Growth– Sexually reproducing
organisms develop from a single cell (zygote)
• Repair– Replace cells that die from
normal wear and tear or accidents
A single-celled
eukaryote (amoeba)
reproduces
Sand dollar embryo after
the egg divided to
form 2 cells
Dividing bone marrow cells produce new blood cells
More….
1. How many daughter cells are produced by mitosis?
2. How does the number of chromosomes in eachdaughter cell compare with the number ofchromosomes in the original parent cell after mitosis? 3. When are chromosomes replicated? 4. During cytokinesis plant cells form a _________while animal cells form a ____________.
ANSWERS:1. How many daughter cells are produced by mitosis? 2
2. How does the number of chromosomes in eachdaughter cell compare with the number of chromosomesin the original parent cell after mitosis? Same numberand type of chromosomes.
3. When are chromosomes replicated? Interphase, specifically S-phase
4. During cytokinesis plant cells form a cell plate whileanimal cells form a cleavage furrow.
Meiosis
Two rounds of cell division
In humans, each daughtercell has 23 chromosomes
Many possible combinations of chromosomes are possible
Random assortmentCrossing over
Not identical in human males and females
Feature Males Females
When does meiosis begin?
How long does each step take?
Begins at puberty
Each step takes about the same time (~64 days total)
Begins during embryonic development
May remain in meiosis I for decades (may never complete meiosis)
How is meiosis completed? Spermatocytes will complete meiosis
Meiosis II happens only with fertilization
How many gametes are formed?
4 spermatids are formed One ovum is formed
ANIMATION OF MEIOSIS
Classical Genetics
MENDELIAN PRINCIPLES OF INHERITANCE
Mendel’s Genetics
Experiment with Peas
Pea Characters Investigated
Pea Characters Investigated
MENDEL’S RULE OF HEREDITY
PUNNETT SQUARE: Monohybrid Cross- single trait factorEXAMPLE : seed shape round (RR) is dominant over wrinkled (rr)Problem: Predict the outcome of a cross when a homozygous dominant round pea is cross with a homozygous wrinkled pea plant
RR
r
r
Rr Rr
Rr Rr
PR: 100 % ROUND
GR: 100 % Rr
Gametes RY Ry rY ry
RY
Ry
rY
ry
Dihybrid Cross: two factor crossSeed Shape: Round (RR). WrinkledSeed Color: yellow (YY) and green (yy)
Parents’ genotype: RrYy x RrYy
RRYy
RRYY RRYy
RrYY RrYy
RrYy
RrYy
RrYy
RRyy
RrYY
rryy
rrYY
Rryy
Rryy
rrYy
rrYy
A or O
A or AB
“Tell me and I will forget, Show me and I might
remember, Involve me and I will
understand.” Chinese Proverb
Thank You