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Science 9 Notes Name: _____________
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6.1 Meiosis
Meiosis is an important aspect of ______
reproduction
Sexual reproduction, through theshuffling of DNA, produces genetic
___________.
This variation offspring produces
individuals that may have ____________
over one another.
Role of Gametes
Normal body cells have a ________ chromosome number,
meaning chromosomes occur in ________. In humans, the male and female
each contribute ___ chromosomes - when fertilization takes place, 23 (egg)
+ 23 (sperm) = 46 (________)
The zygote goes on to develop into an ________, and on into a complete
individual. When the time comes, the cycle repeats - humans produce
________ (either egg or sperm) that have half (haploid) the normal number
of chromosomes.
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Science 9 Notes Name: _____________
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Meiosis
Meiosis produces gametes with half the chromosomes compared to _____
________:
Meiosis Events
Meiosis I
Matching chromosome pairs (homologous chromosomes) move to
________ ________ of the cell - two ________ cells result.
Meiosis II
Chromatidsof each chromosome are ________ ________ - the end result
is four ________ ________, each with half the number of chromosomes.
These develop into gametes.
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Science 9 Notes Name: _____________
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Crossing Over
In meiosis I, chromatids of chromosome pairs can
cross over each other and ________ DNA ________ -
this increases genetic possibilities and produces________ ________
Independent Assortment (p.192)
The pairs of chromosomes in meiosis I separate
independently, creating many different
combinations of chromosomes in the daughtercells
Meiosis Details
Gametes do _____ form equallyin males and females
In males, all 4 cells resulting from meiosis develop into sperm.
In females, 1 cell gets most of the cytoplasm and becomes the egg.
Chromosome mutations sometimes occur ______________
Chromosome changes during meiosis can cause changes in thegenetic information. Parts of chromosomes can be inverted, ______,
duplicated or ________ to another spot.
Chromosome mutations can occur because of mutagens
Chromosome changes, sometimes leading to genetic ________ or
_____, can be cause by mutagenssuch as ________ or ________.
Failed separation of chromosomes in meiosis has serious consequences
Failed separation means that a gamete may end up with no
chromosome or too many of a chromosome. Zygotes that result from
these gametes ________ ________, and if they do, they will have
serious ________ ________.
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Science 9 Notes Name: _____________
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Genetic Disorders
The chromosomes of an individual can be studied
By using a karyotype, geneticists can view an individuals chromosomes.
Certain genetic disorders or syndromes occur when there are specific
chromosomes ________ or ________
Down syndrome usually occurs when there is an extra 21st
chromosome
6.2 Sexual Reproduction
Sexual reproduction brings non-identical gametes together to form a new
________ - it occurs in 3 stages:
Mating- the process by which
___________________________
at same place and same time
Fertilization- process by which_________________________ to
form a new organism
Development- the process by
which an organism develops as
an embryo
Downs Syndrome - 3
chromosomes of chromosome 21
2 chromosomes of
chromosome 21
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Science 9 Notes Name: _____________
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Methods of Fertilization
External or Internal Fertilization
In order for either of these methods to produce a successfully developing
embryo, certain conditions must be met:
1.
Embryo must have enough ________.
2.
Temperature must not be too ________ or too ________.
3. There must be enough ________ so that embryo does not dry out.
4. Embryo must be protected from ________ and items in environment that
can potentially harm it.
External Fertilization
In external fertilization,
sperm and egg join ________
parents
Advantages
Very ________ ________
required to mate
________ ________ of
offspring produced
Offspring can be spread widely in the environment - less competition
between each other and parents
Disadvantages
Many gametes ______ _ ___ ____ ________ Many eggs will ______ _ ___ ____ ________
Offspring are often not protected by parents, so ______ __ _________ ____
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Science 9 Notes Name: _____________
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Pollination
Most plants transfer male gametes as pollen. Pollen can be carried by ____
or other ________.
Colorful flowers can attract bees and other insects. They feed on plant_______ (sugars) and in the process _______ ________ from plant to plant.
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Science 9 Notes Name: _____________
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Embryonic Development
Embryonic development is the early development of an
organism - in humans; it is the ____________________________________.
Stages
End of the first week - ball of cells called morula
By end of second week it is a hollow ball called a blastula
Cells at this stage are _______ _______, and have the ability to develop
into _______ _______ _______ _______
In the next stage the embryo is known as a gastrulaand develops 3 layers:
ectoderm (skin, nerves), mesoderm (muscles, bones), and endoderm (lungs,liver, digestive system lining)
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Science 9 Notes Name: _____________
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Fetal Development
The cell layers now differentiate into the _______ and _______ of a baby - this is
divided into 3 trimesters.
First Trimester (0-12 weeks)
Organ systems begin to develop and form. _______ cells form.
Second Trimester (12-24 weeks)
_______ growth from 12-16 weeks.
Third Trimester (24+ weeks)
Continued growth, especially of _______. _______ begins to deposit at 32
weeks to keep baby warmat birth.
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