Cell cyckle Flashcards
What is the human life cycle based on?
A regular pattern of meiosis and mitosis
What is alternation of generation?
The alternation of diploid and haploid generations.
How do bacteria replicate?
Binary fission
What is the haploid generation of a plant called?
Gametophyte
What are the advantages of sexual reproduction?
Offers a population a way to adapt to a changing environment.
Pairing of homologous chromosomes and crossing over opportunities to replace or repair damaged chromosomes and increase variation
What are the advantages of asexual reproduction?
What is karyotyping?
A method of identification of chromosomes.
What is nondisjunction?
When chromosomes don’t separate properly during anaphase I or II.
What is trisomy?
When one pair of chromosomes is a triplet.
What is monosomy?
When one pair of chromosomes is a singlet.
What is a somatic cell?
A cell that has DNA from maternal and paternal sides combined (diploid = 2(n)).
What is a gamete cell
A cell that only holds half the DNA from the somatic cell from which it came (haploid = n).
: What does meiosis do?
Reduces chromosome number from 2n to n by copying chromosomes once, but dividing twice.
What are the steps of meiosis?
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
What happens in prophase I?
Chromatin condenses into chromosomes.
Centrioles move to opposite poles and spindle fibers appear.
Homologous chromosomes pair up side by side (synapsis) by corresponding genes, forming a tetrad (4 chromatids).
Homologous chromosomes overlap and occasionally break and exchange identical-sized segments (crossing over).
The nuclear envelope disappears.
The nucleolus becomes invisible.
What happens in metaphase I?
Homologous pairs move to the center, with centromeres on either side of the equator.
What happens in anaphase I?
Homologous pairs separate (not sister chromatids separating at the centromere).
Chromosomes move to opposite poles (segregation).
There should be 23 replicated chromosomes at each pole (sister chromatids remain intact).
What happens in telophase I?
Chromosomes are at opposite ends.
Chromosomes do not uncoil to form chromatin.
Nuclear envelope occasionally reappears (in some cells).
Cytokinesis occurs.
What happens in prophase II?
Centrioles move to opposite poles.
New spindle fibers form.
What happens in metaphase II?
The cell moves directly to metaphase II (no DNA replication and no formal organization of the nucleus).
: What happens in anaphase II?
Spindle fibers shorten, and chromatids separate at centromeres.
Chromatids move to opposite poles.
There should be 23 single-stranded chromosomes at each pole.
What happens in telophase II
Chromosomes at opposite ends un-condense to form chromatin.
Nuclear envelope reappears.
Cytokinesis occurs.
What is the result of meiosis?
Four haploid daughter cells, each containing single chromosomes.
