Biology Chapter 13 - Meiosis

# of somatic cell

46 chromosomes, 2 of each 23 types

autosomes

Any chromosome that is not a sex chromosome

Germ cell

Cells that lead to the production of gametes. Produced by meiosis.

Gametes

Cells with the haploid number of chromosomes. Gametes are created out of germ cells. The sperm and eggs involved in sexual reproduction are gametes.

What is the main difference between the events of anaphase 1 and those of mitotic anaphase?

During anaphase, maternal and paternal sister chromatids are separated to opposite ends of the cell via microtubules. In anaphase 1 of meiosis, the maternal homologous pair and the paternal homologous pair are separated to opposite ends of the cell before division.

Metaphase 1

The third stage of the first meiotic division (meiosis I), during which chromosomes align at the center of the cell by way of microtubule force.

Diploid number

The total number of chromosomes present in a cell. Two chromosome sets - (2n)

zygote

fertilized diploid egg

Human/animal sexual life cycle

gametes are the only haploid cells. Meiosis occurs in germ cells during production of gametes, no further cell division prior to fertilization after fertilization, diploid zygote divides by mitosis, producing multicellular diploid organism.

life cycle

generation-generation sequence of stages in the reproductive history of an organism. begins when a haploid sperm fuses with a haploid egg.

clone

group of genetically identical individuals

genes

heriditary units that carry incoded information

sexual reproduction

two parents give offspring unique combination of genes

Homologous pair

"Refers to two similar chromosomes in a diploid cell. One chromosome is derived from the father gamete cell and the other from the mother gamete. same but differ in function - mirror images? Females are XX males are XY

Genetic Reassortment

A process in which DNA packaged as a chromosome is broken and fragments are exchanged with another independent chromosome. Occurs during prophase 1 of meiosis.

Meiosis

A type of cellular reproduction that results in the formation of four haploid cells from one diploid cell. Contains two cellular divisions that follow only one round of DNA replication. The type of reproduction that produces germ cells.

Somatic cell

Any plant or animal cell that is not a germ cell. The class of cell formed during mitosis. Diploid number 2n=46

Is the process of DNA replication different in meiosis versus mitosis? What are the products of DNA replication in meiosis?

DNA replication occurs through the same mechanisms in both meiosis and mitosis. After replication, a maternal homologue and its copy, or sister chromatid become closely associated. The same thing happens with the original paternal homologue. DNA replication results in two homologous pairs of chromosomes.

Cells entering the second round of meiosis have a ________ number of chromosomes. After cell division, they have a _________ number of chromosomes. This is because meiosis leads to the production of _________ cells.

Diploid. Haploid. Germ.

What occurs during genetic reassortment?

During genetic reassortment, portions of one of the chromosomes in each homologous pair break off and exchange. This leads to a small piece of the maternal homologue becoming a part of the paternal homologue and vice versa.

During what phase of meiosis does genetic reassortment take place?

During prophase 1.

What is the difference between mitotic interphase and the meiotic interphase that separates the two rounds of division?

During the long mitotic interphase, cells undergo a number of preparations for cell division. These include monitoring of cell size and environment and DNA replication. The interphase that separates the two meiotic divisions is much shorter than mitotic interphase and no DNA replication takes place. In meiotic interphase, brief chromosome decondensation may occur.

What is the purpose of the genetic reassortment, or cross-over, that occurs in meiosis?

Genetic reassortment provides for genetic variability in offspring cells. Unlike in mitosis where a cell reproduces an exact copy of itself, meiosis involves genetic recombination that leads to similar, but new and diverse cells.

During mitosis, chromosomes are separated by microtubules attached to their their _________. In meiosis, on the other hand, a microtubule attaches to a structure called a _________.

Kinetochores or centromeres. Chiasma.

What is the name of the phase of the second meiotic division in which chromosomes align at the center of the cell?

Metaphase 2.

Are the sister chromatids present in a cell in prometaphase 1 identical?

No. While they are very similar, sister chromatids in prometaphase 1 are slightly different because of the small segment of crossover between parental homologous pairs that results from prophase 1 genetic reassortment.

Microtubule

One of three protein components of the cytoskeleton. Long, cylindrical structures approximately 25 nanometers in diameter. Extend from the centrosome to all parts of the cell, forming tracks on which organelles can travel within the cell.

What is the name of the region of physical connection between maternal and paternal homologous pairs where recombination takes place?

The chiasma.

Telophase 1

The fifth and final stage of the first meiotic division (meiosis I), during which chromosomes arrive at the poles of the cell and begin to recondense.

Telophase 2

The fifth and final stage of the second meiotic division (meiosis II), during which chromosomes arrive at the poles of the cell, the nuclear envelope begins to reform, and the chromosomes begin to recondense.

Which of the following pairs of cells could likely be products of meiotic division II?

The first pair is the most likely product of meiotic division II for two reasons. First, the cells each contain a haploid number of chromosomes. Second, the chromosome in one of the products contains a region of genetic crossover.

Prophase 1

The first stage of the first meiotic division (meiosis I), during which genetic reassortment takes place. Can be very long occupying up to 90% of the entire duration of meiosis.

Prophase 2

The first, brief stage of the second meiotic division (meiosis II), during which condensed chromosomes are visible.

Anaphase 1

The fourth stage of the first meiotic division (meiosis I), during which maternal and paternal homologous pairs are separated on microtubules.

Anaphase 2

The fourth stage of the second meiotic division (meiosis II), during which either maternal or paternal sister chromatids are separated on microtubules.

Haploid number

The number of unique chromosomes or homologous pairs in a cell. Half the diploid number. (n)

Chiasma

The region of physical linkage between maternal and paternal homologous pairs during genetic reassortment. Marks the location of crossover between two nonsister chromatids.

Prometaphase 1

The second stage of the first meiotic division (meiosis I), during which the nuclear envelope breaks down, allowing microtubule access to chromosomes.

Prometaphase 2

The second stage of the second meiotic division (meiosis I), during which microtubules attach to chromosomes.

Metaphase 2

The third stage of the second meiotic division (meiosis II), during which chromosomes align at the center of the cell by way of microtubule force.

sex chromosomes

X and Y chromosomes (females have XX and males have XY)

Plant/algae sexual life cycle

alternation of generations includes both diploid and haploid stages that are multicellular - sporophyte meiosis produces haploid cells called spores does not fuse with another cell, divides mitotically - generates multicellular haploid state called gametophyte. two gametes produced by mitosis fertilization results in diploid zygote - develops into next sporophyte generation

Fungi/protists sexual life cycle

gametes fuse and form diploid zygote, meiosis occurs without multicellular diploid offspring. Meiosis produces haploid cells that divide by mitosis to either unicellular descendants or haploid multicellular adult organism. Only diploid stage is in single-celled zygote.

Which of the following figures represents likely resulting cells of the first meiotic division?

http://img.sparknotes.com/figures/2/29a9dc6524dd09bf44944909a4263dd1/problem2.gif Figure 3, on the far left is the more likely product of the first meiotic division for two reasons. First, its diploid pairs stem from only one parental source. Second, it contains regions of genetic crossover

karyotype

ordered display of human chromosome pairs

genetics

scientific study of heredity and variation

meiosis I

separates homologous chromosomes. Centromeres divide and sister chromatids move to opposite poles to become individual chromosome

asexual reproduction

single individual is the sole parent and passes copies of its genes to offspring

locus

specific location along the length of a chromosome

meiosis II

the second phase of meiosis consisting of chromatids separating, along with the two diploid cells splitting in two

heredity

transmission of traits from one generation to another. Also called inheritance

fertilization

union of gametes, fusion of their nuclei

Which is the longest phase of meiosis?

Prophase 1 can last up to 90% of the entire duration of meiosis because the very important genetic reassortment event occurs during it.

How is prophase 1 different from prophase 2?

Recall that during prophase 1, genetic reassortment takes place. As a result, prophase 1 can last many days. During prophase 2, no further genetic reassortment occurs and therefore it lasts only a short time compared to prophase 1.

Sister chromatid

Refers to the copy of a chromosomes that results from DNA replication and is still closely linked to its original.