ch. 7 meiosis & sexual reproduction. what if… a human sperm & egg each had 46 chromosomes,...
TRANSCRIPT
Ch. 7 Meiosis & Sexual Reproduction
What if…
What if… A HUMAN sperm & egg each had 46 chromosomes, like other human body cells, how many chromosomes would a zygote have?
Why might an increase in the number of chromosomes a human cell has cause problems?
WHITEBOARDS
Draw the gametes for males and females
Inside each sex cell, give the number of chromosomes
Below your drawing, write whether the sex cells are haploid or diploid
If an organism’s sex cells have 12 chromosomes, how chromosomes will a body cell have?
Meiosis- Formation of Haploid Cells
Meiosis 1. DNA in the original cell replicated
2. Meiosis halves the number of chromosomes when forming gametes or spores
Still occurs in the nucleus!
Draw it out!
Meiosis Look at your books (p. 144) and your notes for pictures of Meiosis I & II
Draw your assigned stage on the board – be ready to explain it!
Meiosis I
Meiosis
Meiosis II
Meiosis
Hold them up!
Meiosis Hold up the number of cells produced at the end of Meiosis I
Hold up the number of cells produced at the end of Meiosis II
Hold up the number of sets of chromosomes in one haploid cell at the end of Meiosis II– 2 Sets = 46 chromosomes– 1 Set = 23 chromosomes
Meiosis- Formation of Haploid Cells
Meiosis 4 haploid cells result at the end of Meiosis II
Think – Pair - Share
Genetic
Variation
What does the term “genetic variation” mean?
How important is genetic variation to the survival of our species?
Importance of Genetic Variation
Importance of genetic variation
1. Meiosis and the joining of gametes are essential to evolution
No genetic process generates variation more quickly
2. Evolution appears to increase with increases in genetic variation
Meiosis & Genetic Variation
Genetic Variation
1. Independent Assortment-– In humans, each gamete receives 1
chromosome from each of 23 pairs of homologous chromosomes ( = 23 total chromosomes = 1n)
– Which of the 2 homologues each offspring receives is a matter of chance
– 8 million different gamete combinations can result
Meiosis & Genetic Variation
Genetic Variation
2. Crossing Over- – DNA exchange during Prophase I
in Meiosis– Portions of a chromatid on 1
homologous chromosome are broken & exchanged with the chromatid portions of the other homologous chromosome
This recombination GREATLY increases genetic variation
-How is this different from translocation? -Crossing over occurs between
homologouschromosomes-Translocation is with non-homologous chromosomes
Meiosis & Genetic Variation
Genetic Variation
3. Random Fertilization- two gametes are randomly joined to form a zygote– 64 trillion possible outcomes
Genetic Variation - Importance
Importance of genetic variation
Breeding larger or faster animals can be limited until enough genetic variation is eventually generated to continue the breeding
Genetic Variation Importance
Importance of genetic variation
4. Natural selection doesn’t always favor genetic change– Existing conditions may be
favorable, slowing evolution
Meiosis- Formation of Haploid Cells
Meiosis Pages 148 – 149
Boys do Spermatogensis
Girls do Oogenisis
Meiosis- Formation of Haploid Cells
Meiosis in Males
SPERMATOGENESIS- produce sperm in the testes of male animals– A. Diploid cell increases in size to
germ cell– B. Undergoes meiosis I– C. Undergoes meiosis II to form 4
haploid cells– D. 4 cells develop tail (sperm)
Meiosis- Gamete Production
Meiosis in females
OOGENESIS- produces eggs in the ovary of female animals– A. Diploid cell increases in size to
a germ cell– B. Undergoes meiosis I- cytoplasm
splits unevenly into each egg cell– C. Undergoes meiosis II- more
uneven cytoplasm distribution– D. One large egg cell develops, 3
polar bodies that do not survive
Meiosis vs. Mitosis
Meiosis vs. Mitosis
Mitosis –– Division of somatic (body) cells– Diploid (2n)– Creates identical cells
Meiosis – •Division of chromosomes to
form reproductive cells•Haploid (n) sex cells
produced•Genetic variation
Sexual Life Cycles in Eukaryotes
Life Cycle Entire span in the life of an organism from one generation to the next
Sexual Life Cycles in Eukaryotes
Sexual Haploid Life Cycle
1. Zygote is diploid but undergoes meiosis immediately to make new haploid cells (any DNA damage is repaired)
Sexual Life Cycles in Eukaryotes
Sexual Haploid Life Cycle
2. Haploid cells create haploid individuals
3. Gametes are produced by mitosis
Sexual Life Cycles in Eukaryotes
Sexual Haploid Life Cycle
4. Gametes fuse to produce diploid zygote, cycle continues
Occurs in protists, fungi, algae, chlamydomonas
Sexual Life Cycles in Eukaryotes
Sexual Diploid Life Cycle
1. Adults are diploid, each inheriting characteristics from both parents
2. Diploid reproductive cells undergo meiosis to produce gametes
Sexual Life Cycles in Eukaryotes
Sexual Diploid Life Cycle
3. Fertilization- joining of gametes (sperm and egg)
4. Resulting zygote divides by mitosis
Sexual Life Cycles in Eukaryotes
Sexual Diploid Life Cycle
5. Cells of adult also end up diploid
6. All cells involved are diploid, except gametes which are haploid
Ex: Humans/ Animals
Sexual Life Cycles in Eukaryotes
Alternation of generations
1. Often in plants, alternates between haploid and diploid phases
Sexual Life Cycles in Eukaryotes
Alternation of generations
2. Sporophyte- diploid phase in plant life cycle that produces spores– Spore forming cells undergo
meiosis to produce spores (haploid reproductive cell that become an adult without fusing with another cell)
Sexual Life Cycles in Eukaryotes
Alternation of generations
3. Gametophyte- haploid phase in plant life cycle that produces gametes through mitosis– Gametes fuse and give rise to
diploid phase
Sexual Life Cycles in Eukaryotes
Alternation of generations
4. Ex: Moss– Stalk tip’s capsule pops off scattering
haploid spores– Spores germinate by mitosis and form
gametophytes– Male gametophyte releases sperm that
swim through film of moisture to eggs in female gametophyte
– Diploid zygote develops as sporophyte within the gametophyte
– Cycle continues
Cloning by parthenogenesis
Cloning by parthenogenesis
1. A new individual develops form an unfertilized egg
2. No male involved, offspring is genetic clone of mother
3. Mother’s own chromosomes are copied in place of the male’s
4. Occurred in females without male companionship for long periods of time
5. Dandelions, hawkweeds, fish, lizards, frogs, snakes, male drone honeybees, NO MAMMALS
Assessment
Identify the type of reproduction that results in offspring that are genetically identical to their parent
Describe two different types of eukaryotic asexual reproduction
Compare the haploid life cycle found in chlamydomonas with a diploid life cycle
Summarize the process of alternation of generations
Evaluate the significance of mutations and repair of mutations to the evolution of sexual reproduction