Terms in this set (27)
Asexual (vegetative) reproduction
Example, a new plant grows out of the root or a shoot from an existing plant.
Produces only genetically identical offspring since all divisions are by mitosis.
Offspring called clones meaning that each is an exact copy of the original organism
This method of reproduction is rapid and effective allowing the spread of an organism
Since the offspring are identical, there is no mechanism for introducing diversity
Formation of new individual by a combination of two haploid sex cells (gametes).
Fertilization- combination of genetic information from two separate cells that have one half the original genetic information
Gametes for fertilization usually come from separate parents
Female- produces an egg
Male produces sperm
Both gametes are haploid, with a single set of chromosomes
The new individual is called a zygote, with two sets of chromosomes (diploid).
Meiosis is a process to convert a diploid cell to a haploid gamete, and cause a change in the genetic information to increase diversity in the offspring.
Chromosomes in a Diploid Cell
Diploid set for humans; 2n = 46
Autosomes; homologous chromosomes, one from each parent (humans = 22 sets of 2)
Sex chromosomes (humans have 1 set of 2)
Female-sex chromosomes are homologous (XX)
Male-sex chromosomes are non-homologous (XY)
A pictorial display of metaphase chromosomes from a mitotic cell
Homologous chromosomes- pairs
Ploidy: Number of sets of chromosomes in a cell
Haploid (n)-- one set chromosomes
Diploid (2n)-- two sets chromosomes
Most plant and animal adults are diploid (2n)
Eggs and sperm are haploid (n)
What is meiosis I?
In meiosis I, chromosomes in a diploid cell resegregate, producing four haploid daughter cells. It is this step in meiosis that generates genetic diversity
DNA replication precedes the start of meiosis I. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. Chromosomal condensation allows these to be viewed in the microscope. Note that the bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.
The nuclear membrane disappears. One kinetochore forms per chromosome rather than one per chromatid, and the chromosomes attached to spindle fibers begin to move.
Bivalents, each composed of two chromosomes (four chromatids) align at the metaphase plate. The orientation is random, with either parental homologue on a side. This means that there is a 50-50 chance for the daughter cells to get either the mother's or father's homologue for each chromosome.
Chiasmata separate. Chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but each chromosome has two chromatids.
Nuclear envelopes may reform, or the cell may quickly start meiosis II.
where two complete daughter cells form.
Comparing Meiosis and Mitosis
Mitosis: Homologous chromosomes independent
Meiosis: Homologous chromosomes pair forming bivalents until anaphase I
Chromosome number- reduction in meiosis
Mitosis- identical daughter cells
Meiosis- daughter cells haploid
Genetic identity of progeny:
Mitosis: identical daughter cells
Meiosis: daughter cells have new assortment of parental chromosomes
Meiosis: chromatids not identical, crossing over
A human cell has 46 total or 23 pairs of chromosomes. Following mitosis, the daughter cells would each have a total of ______ chromosomes. After meiosis I, the two daughter cells would have _____chromosomes, and after meiosis II ______ chromosomes.
46, 23, 23 (The chromosome number is reduced to one half during the first meiotic division. Recall that the number of chromosomes is determined by the number of centromeres, and not the number of chromatids.)
The process of meiosis produces four cells with nonidentical chromosomes. This diversification occurs during:
prophase 1,Prophase I includes recombination of genetic material and the random arrangement of the homologous pairs, producing diversification of the resulting haploid cells.
Which of the following is unique to mitosis and not a part of meiosis?
A. homologous chromosomes pair forming bivalents
B. homologous chromosomes cross over
C. chromatids are separated during anaphase
D. homologous chromosomes behave independently
The stage of meiosis where cells become haploid
anaphase I (Separation of homologous pairs occurs at anaphase I. Even though each chromosome has two chromatids, the total number of chromosomes is 23 for humans after anaphase I of meiosis I. Recall that the number of chromosomes is determined by the number of centromeres.)
One of the earliest events that distinguishes meiosis occurs in prophase I and involves:
. Condensation of chromosomes
B. Loss of the nuclear membrane
C. Movement of chromosomes towards the metaphase plate
D. Pairing of homologous chromosomes
Answer is D
Coral in the ocean grows by budding, where the new organism grows out of the old one by mitosis. This form of replication is an example of:
_________________ most closely resembles events of mitosis except that the cells are ___________.
meiosis II, haploid
Meiosis II events are similar to mitosis with haploid cells.
During anaphase, a free kinetochore formed by disrupting an attached spindle fiber results in an immediate block to the process. This result shows that:
The cells have mechanisms to insure that errors are not made during anaphase.
Mutated genes that are capable of causing death.
Alleles of different genes are assorted independently of one another during the formation of gametes
mendel's law of independent assortment
Alleles segregate from one another during the formation of gametes.
mendel's law of segregation
The stage of the cell cycle where the cell is preparing to begin DNA replication is called:
Prior to cell division, each chromosome replicates or duplicates its genetic material. The products are connected by a centromere and are called:
Cytokinesis in a plant cell is characterized by
the formation of a cell plate in the cytoplasm
The spindle fibers are used to bring in vesicles that line up along the cell plate and produce a new cell wall.