Lesson 3: G3 - Sexual Reproduction Flashcards
What are the 2 key process of sexual reproduction?
1) formation of haploid cells, or gametes, which contain genetic information from the parents
2) Two sex cells joining to form a zygote, the first cell of a genetically unique individual, through fertilization
Types of fertilzation methods
- Gamtes fuse to form zygote
- Insects pollinating
-External fertilzation
-Interal fertilzation
sex cells are produced through…
meiosis
-This is the process through which haploid gametes are formed
TRUE OF FASLE: in meiosis chromosome # in each generation is cut in half
TRUE
How many chromosomes do sex cells contain?
23 Chormosomes
combination of two gametes (sperm and egg - both haploid) will result in…
omplete set of chromosomes (diploid, 2n = 46)
homologous chromosomes
You receive a complete set of DNA from each parent (one version of each gene)
-ensures the offspring is genetically unique from each parents
Meiosis is a process that involves __#__
divisions that produces __#__ haploid gametes from _#__ diploid parent cell
Meiosis is a process that involves two divisions that produces 4 haploid gametes from 1 diploid parent cell
gametogenesis
formation of sex cells
Formation of sperm
spermatogenesis
ormation of egg cells or ova
oogenesis
spermatogenesis and oogenesis formed through process called…
meiosis
Steps in Meiosis
- Interphase
-Meiosis I: Prophase I
-Meiosis I: Metaphase I
-Meiosis I: Anaphase I
-Meiosis I: Telophase I
-Meiosis II: Prophase II
-Meiosis II: Metaphase II
-Meiosis II: Anaphase II
-Meiosis II: Telophase II
Interphase
Cell grows to nearly twice in size
Nucleus makes a copy of its DNA
Organelles are also replicated
Meiosis I: Prophase I
Chromatin condenses into chromosomes
The nuclear membrane dissolves
Centrioles move to opposite sides of the cell
Spindle fibers begin to grow
Homologous chromosomes come together and intertwine to form a tetrad by a process called synapsis
Each chromosome is made of 2 sister chromatids, and you have 1 chromosome from each parents
These four sister chromatids together is called a tetrad
Crossing over can also occur at this stage:
-This is when intertwined chromatids from different chromosomes break off and reattach at the chiasmata
-This causes an exchange of genetic material at certain sections
-This works to mix or recombine genetic information further increasing genetic variation in the gene pool
synapsis
intertwinning of chromosomes
Meiosis I: Metaphase I
tetrads migrate towards the center of the cell, called the equatorial plate
This is accomplished through spindle fiber
attachment at the centromeres like in mitosis
The tetrads align their centromeres at the middle of the cell
Meiosis I: Anaphase I
Homologous chromosomes move to opposite poles of the cell when the spindle fibers shorten
-means that only one of the two chromosomes from each homologous pair will be in each new daughter cell and therefore are genetically unique
Meiosis I: Telophase I
The nuclear membranes reform, spindle fibers dissolve and the cell begins to divide via the first cycle of cytokinesis
Each new cell has only 1 (not two) duplicated copy of a chromosome at this point
Only the maternal or paternal chromosome is in each new cell
Therefore the cells are haploid
Meiosis II: Prophase II
Each haploid cell has one chromosome made of two sister chromatids at this point
The sister chromatids are not genetically identical though, due to the crossing over that occurred during prophase I
Once again, the nuclear membrane dissolves, centrioles move to opposite poles and spindle fibers reform
Meiosis II: Metaphase II
Again, the one chromosome made of two sister chromatids move to center of the cell, called the equatorial plate
This is accomplished through spindle fiber attachment at the centromeres like in mitosis
The chromosomes align their centromeres at the middle of the cell
Meiosis II: Anaphase II
Sister chromatids now separate and move to opposite poles of the cell
Each cell now has a single sister chromatid, not a duplicate copy
These will not be identical due to the genetic exchange that occurred in crossing over
Meiosis II: Telophase II
the nuclear membrane reforms around the chromatids, the DNA relaxes into chromatin and the spindle fibers dissolve
The second nuclear division is now completed
Soon after, cytokinesis will occur for the second time
This will result in 4 haploid daughter cells (that are NOT identical)
What stages of meosis allow for gentic variation?
In Prophase I, crossing over occurs randomly
In Metaphase I and II, it is random as to which side each chromosome goes to
