reproduction and meiosis. asexual organisms reproduce differently than sexual organisms. as...
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Reproduction and Meiosis
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Reproduction and Meiosis
• Asexual organisms reproduce differently than sexual organisms.
• As multi-cellular organisms develop, their cells differentiate.
Asexual Reproduction in Paramecium Differentiation in multi-
cellular organism
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How many different species are there?
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There are millions of different species of organisms.
• Each species produces more of its own.– Bacteria splits to make
2 identical bacteria– Palm tress produce
more palm trees– Humans produce more
humans
• The formation of new organisms in a species is called reproduction.
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2 Types of Reproduction
Asexual Sexual
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Asexual
• Asexual reproduction is reproduction that requires only one parent.
• Most single celled organisms, like bacteria and protozoan, reproduce this way.
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Asexual• Cell Division is a type
of asexual reproduction (occurs in body cells)
• In asexual reproduction the DNA and internal structures are copied
• Then the parent cell divides, forming 2 cells that are exact copies of the original.
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To understand sexual reproduction, you first need to know about human body cells.
• Each cell in your body, except for sex cells, has 46 chromosomes.
• These chromosomes are called homologous chromosomes.
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Homologous chromosomes have pairs of matching information, are usually the same size and shape, and have the same number of chromosomes as their parent cells.
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Unlike body cells, human sex cells only have 23
chromosomes.In males these sex cells are called sperm; in females, they are called eggs.
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So, how do these sex cells end up with only half the number of chromosomes?
Through meiotic division
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This process is call Meiosis.
• Meiosis is the process of cell division in which sex cells (eggs and sperm) are formed
• Eggs and sperm are gametes that unite to produce a cell zygote that may develop into an embryo.
Egg 23 Sperm 23
Zygote 46
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During meiosis, a cell undergoes two divisions to produce four sex cells, each with half the number of chromosomes of the parent cell.
Meiosis 1 Meiosis 2
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The chromosomes are copied once and then the nucleus
divides twice.• 4 daughter cells are created from
each parent cell.
Meiosis 1
Meiosis 2
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Each sex cell has half the number of chromosomes found in the parent cell—one of the chromosomes from each homologous pair.
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Diploid & Hapliod Chromosomes
• A complete set of chromosomes is called a diploid set.
• A half set of chromosomes is called a haploid set.
• Most animal cells have a diploid set of chromosomes, except in sex cells.
ChickenDiploid Set = 78Haploid = 39
HumanDiploid Set = 46Haploid = 23
ElephantDiploid Set = 56Haploid = 28
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Fertilization is the union of egg and sperm to form a new
organism.• When an egg is fertilized by a sperm,
the haploid set of chromosomes from the father unites with the haploid set from the mother.
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Will the offspring be male or female?
• Human sex chromosomes carry genes that determine whether the offspring is male or female.– Female have two X
chromosomes (XX)– Males have one X
and one Y chromosome (XY)
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During meiosis, one of each chromosome pair ends up in a sex
cell.• During human sexual reproduction
egg and sperm combine to form either the XX or XY combination– XX=female– XY=male
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A fertilized egg, called a zygote, has a diploid set of
chromosomes.• For each
homologous pair, one chromosome comes from the mother and one from the father.
• After fertilization, the zygote rapidly divides by mitosis and becomes an embryo.
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An embryo is an organism in its earliest stages of
development.• In the developing embryo, cells begin
to differentiate.
Chicken
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The final outcome is a multi-cellular organism with many
different types of specialized cells.
• You have brain cells, stomach cells, and muscle cells to name a few.
• All of those cells can be traced back to the zygote.
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Cell differentiation is the term used to describe the process of
cell specialization.
• For example, cells that eventually divide to become part of the stomach are different from those that will become part of the nervous system.
• As cells differentiate, they give rise to different tissues.
• These tissues eventually form organs.
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Cell differentiation
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As the embryo continues to develop some cells become
even more specialized.
• For example, some cells in the retina of your eye become rod cells (for vision in dim light) and others become cone cells (for color vision).
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• After differentiation is complete, most cells lose the ability to become other types of cells.
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Mitosis Differentiation
and growth
Mitosis Differentiation and growth
Fusion to form Zygote
Zygote
Juvenile
Egg
Sperm
Meiosis