Chapter 18 Flashcards
very long DNA molecule in association with protein
chromosome
segment of DNA in a chromosome
Gene
DNA and protein combined
chromatin
How many chromosomes do humans get from each parent; for a total of how many?
23;46
(2n) two sets of chromosomes
Diploid
chromosome pairs 1-22
autosomes
Female sex chromosome
XX
Male sex chromosome
XY
paired corresponding chromosomes
homologous chromosomes
genetic and phenotypic characteristics
sex
shared genetic background
ancestry
produces a new generation of cells
reproduction
*Division of Somatic cells
*maintains diploid chromosome number
Mitosis
Purpose of Mitosis
growth, replace worn out or dead cells, repair tissue
*Division of germ cells
*Halve the diploid number to haploid
Meiosis
The purpose of Meiosis
first stage in sexual reprodcution
“lifetime” of a somatic cell
Cell Cycle
*3/4 of the cell cycle
*involves G1, S, G2
Interphase
What does G1, S, and G2 stand for in Interphase?
G1: cell growth
S: DNA chromosomes are copied through replication
G2: preparation for mitosis
1/4 of the cell cycle
Mitosis
four phases; chromosomes are sorted into two sets
Mitosis
cytoplasm divides
cytokinesis
chromosome and its copy
sister chromatids
region of attachment to the microtubule
centromere
Once coiling is completed a chromosome has it typical ______ & _________.
size & shape
What are the four stages of Mitosis?
Prophase, Metaphase, Anaphase, Telophase
*Coiling and condensing of the chromosome
*microtubules form into spindle formation
*nuclear membrane begins breaking up
*Microtubules move centrioles to the opposite poles
Prophase
*Nuclear membrane breaks apart
*microtubules penetrate nuclear region
*microtubules interact w/ chromosomes at centromere
prometaphase
Duplicated chromosomes align midway between the poles of the cell
metaphase
These attach to chromosomes and move them?
Spindles
*sister chromatids split; become independent chromosomes
*pulled by microtubules toward the pole region
*spindle elongates, pushing the poles farther apart
Anaphase
*chromosomes no longer connected to the spindle
*chromosomes begin to decondense - again form chromatin
*nuclear envelope forms around each cluster
Telophase
*begins toward end of anaphase
*cleavage furrow forms
Cytokinesis
*microfilaments (actin) pull the plasma membrane inward all around the cell
*pinches the cell in two
cleavage furrow
What do males contribute during sexual reproduction and what do females contribute?
Male = sperm
Female = egg
combines a sperm and an egg to produce the first cell of the new individual (Zygote)
fertilization
In meiosis the parent cell of the nucleus divides how many times?
twice
How meiosis divide the nuclei of germ cells in a way that halves the number of chromosomes in daughter cells; reduces the number to haploid number
Reductional Division
In meiosis what step cause the germ cell to copy its DNA
Interphase
two consecutive divisions of the chromosomes
Meiosis
homologues pair up and then seperate
Meiosis I
Sister chromatids split; four haploid cells formed
Meiosis II
*Chromosomes condense
*each chromosome has two sister chromatids
*crossing over occurs
Prophase I
*Homologous chromosomes move to central plane in pairs
*spindle fibers attach to centromere
*nuclear envelope fragments
Late Prophase to Prometaphase
These are not genetically identical
Daughter Cells
Paired chromosomes are oriented toward opposite poles
Metaphase I
Chromosome disjunction
Independent assortment
Anaphase I
separation of paired chromosomes
chromosome disjunction
separated homologues move toward opposite poles
independent assortment
*reduced chromosomes to 23 in each nucleus
*daughter cells separated by membranes
*chromosomes reach the poles; nuclei forms
Telophase I
*chromosomes attach to a new spindle apparatus
*sister chromatids are attached to spindle fibers from opposite poles
Prophase II
chromosomes align at equatorial plane
Metaphase II
*centromeres split
*chromatid disjunction - sister chromatids move toward opposite poles
Anaphase II
*each chromatid is now called a chromosome
*separated chromatids gather at poles; daughter nuclei (each one contains a haploid set of chromosomes) form
Telophase II
homologous pairs of chromosomes line up at random during what phase?
Metaphase I
disjunction and independent assortment happen when?
Anaphase I
*consists chromatids break at same places along their length
*exchange corresponding segments
Crossing Over
genes may have different chemical forms
Genetic recombination
Where does Mitosis occur?
Somatic Cells
Where does meiosis occur?
germ cells