Post on 22-Jul-2020
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Name: _______________________________ Date: ___________________
6.1 - MeiosisObjectives
• Describe the process of meiosis, Compare and contrast meiosis and
mitosis, Explain why meiosis is needed
Meiosis
• _______________________________– 2 parents – genetic differences
• The process of Meiosis results in the production of special cells called ____________________________
• Gametes have ______________the number of chromosomes as body cells
• Cell division _________________________ in Meiosis
• Once at the end of Meiosis I and again at the end of Meiosis II
• In Meiosis I, _________________________ chromosomes called ________________________
chromosomes separate
• In Meiosis II, ______________________________ separate
• The process of meiosis shuffles genetic information and results in variation of the gametes
• Results in _______________________
Important Terms
• ___________________: half the total number of chromosomes found in gametes (in humans = 23)
• ___________________: total number of chromosomes found in body cells (in humans = 46)
Meiosis
• AKA: Germ cell division or sex cell division
• Purpose: to produce gametes (i.e. sex cells:_________________ and _________________ )
• Products: _________________________ each genetically _____________________ this creates
genetic variability
Fertilization
• 2 gametes come together; in humans an egg and sperm come together
• Each has _______ chromosomes, thus together there are _____ in the zygote
Meiosis: Reducing Chromosome Number
Meiosis: Chromosome Number Sequence
Meiosis – Prophase I
Parent
All genetically
• Chromosomes coil and become visible.
• Nuclear membrane ______________________ & Spindle fibers form.
• ___________________________ chromosomes move towards each other and pair.
Meiosis – Metaphase I
• _____________ of homologous chromosomes move to the ___________ of the
cell.
• These pairs are aligned on either side of the metaphase plate.
Meiosis – Anaphase I
• _________________________ chromosome _________ are pulled ____________
from each other towards opposite ends of the cell. Paired chromatids
remain__________________.
Meiosis - Telophase I
• Paired chromatids may uncoil and become less visible.
• Nuclear membranes may form around each chromosome cluster.
• Spindle fibers _______________________ and ____________________ occurs.
Meiosis II
• Phase II of meiosis is the __________________________________________ of haploid cells.
• Although there will be _____________________________________________ cells at the end of meiosis
II, all other processes for this division are similar to mitosis.
Meiosis II – Prophase II
• Paired chromatids coil.
• Spindle fibers form
• Nuclear membrane disappears.
Meiosis II – Metaphase II
• Paired chromatids __________________ in the middle of the cell.
• The ____________________________ are attached to spindle fibers.
Meiosis II – Anaphase II
• Each pair of chromatids split at the ________________ to form two ____________
______________________________.
• Chromosomes move to opposite ends of the cell.
Meiosis II – Telophase II
• Chromosomes uncoil and become less visible
• _______________________________ form around _______________________
• Spindle fibers disappear
• Cytokinesis occurs.
Meiosis - Cytokinesis
• Same process as in mitosis
• Four ___________________________ cells are formed.
• These cells are called haploid cells (n).
• # chromosomes = ___________________________ of chromosomes of parent
cell.
Meiosis Events:
Meiosis I
• Matching chromosome pairs (homologous chromosomes) move to
opposite poles of the cell - two daughter cells result.
Meiosis II
• Chromatids of each chromosome are pulled apart - the end result is four haploid cells, each with half
the number of chromosomes. These develop into gametes.
Crossing Over
• Important event that occurs _______________________
each chromosome pair in meiosis I
• There is an ______________________________ of
segments of ________________________ and picks up
new genetic information
Independent Assortment:
• This occurs when homologous pairs of chromosomes _________________________ at the equator and
move towards opposite poles of the cell.
Fertilization
• There are more than _____________ combinations possible for these 23 pairs in any egg or sperm cell
• When fertilization occurs, ________________________________ different zygotes are possible from
the combination of one sperm cell and one egg cell!
Gamete Formation
• Males produce ____________________ for every round of meiosis
• Females produce ____________________________ for each round of meiosis: 3 of the 4 “eggs”
produced die off - called polar bodies
• All the cytoplasm, nutrients and energy gets put into one egg
Chromosome Mutations
• Sometimes occur spontaneously
• Chromosome changes during meiosis can cause changes in the genetic information.
• Parts of chromosomes can be inverted, _________________________, duplicated or
___________________to another spot.
Occur because of mutagens
• Chromosome changes, sometimes leading to genetic disease or death, can be caused by mutagens such as
radiation or chemicals.
Can occur if there is failed separation of chromosomes in meiosis
• Failed separation means that a gamete may end up with _______ chromosome or ________________ of a
chromosome.
• Zygotes that result from these gametes rarely survive, and if they do, they will have serious genetic
disorders.
Diagnosing Genetic Disorders
• A geneticist can prepare a different type
of picture for individuals that show
all chromosomes called ______________________________
• By analyzing karyotypes, geneticists can determine whole chromosome mutations
• Can diagnose genetic disorders or syndromes
• Down syndrome – most frequent genetic disorder - Caused by an extra ________________ chromosome
Meiosis Overview