Meiosis Flashcards
Define homologous chromosomes
a pair of chromosomes that code for the same trait
How many homologous chromosomes are in humans?
23
What is a karyotype
an ordered display of the pairs of homologous chromosomes from a cell
are called X and Y
sex chromosomes
What are autosomes
The 22 pairs of chromosomes that do not determine sex (determine everything else)
What does meiosis make
four haploid (n) gametes
What is a zygote
Egg and sperm united to form a diploid
What is the longest phase of meiosis?
Prophase I
What two main things happen in prophase I?
Synapsis
Crossing over
What is synapsis?
homologous chromosomes pair up
What is a tetrad
Sister chromatids connnected to other homologous sister chromatids
What is crossing over
homologous chromosomes exchange DNA while connected as tetrads
The point at which homologous chromosomes connect to exchange DNA is called the ______
Chiasma
In metaphase I, tetrads line up at the __________ _____
metaphase plate
What is independent assortment
homologous chromosomes line up randomly on any side
In anaphase I, what happens to the tetrads?
tetrads separate (homologous chromosomes are separated)
In anaphase I, what happens to the sister chromatids?
they remain attached at the centromere and move as one unit toward the pole
Crossing over
produces ________ chromosomes
recombinant
Define recombinant chromosomes
new combinations of chromosomes, which combines genes inherited from each parent
How is prophase II of meiosis II similar to mitosis?
spindle fibers and kinetochores form
How is metaphase II of meiosis II similar to mitosis?
chromatids line up
How is anaphase II of meiosis II similar to mitosis?
chromatids are separated into individual chromosomes
How is telophase II and cytokinesis of meiosis II similar to mitosis?
each cell splits, and nuclei reform (4 unidentical haploid cells are now present)
What three mechanisms contribute to genetic variation?:
Independent assortment of chromosomes
Crossing over
Random fertilization
Describe independent assortment of chromosomes
The number of combinations possible when chromosomes assort independently into gametes is 2^n, where n is the haploid number
How does random fertilization add genetic variation
any sperm can fuse with any egg
An egg and sperm can make about __ _______ diploid combinations
70 trillion
Describe three events that occur during meiosis I but not mitosis
- Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information
- At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes
- At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate
