DNA Into Chromosomes Flashcards
How is DNA arranged?
It is arranged into fibers called chromatin
What does DNA wrap around to form nucleosomes
histone
What do nucleosomes condense into
chromatin
what do chromatin condense into
chromosomes
Define genome
The complete DNA sequence in every cell of an organism
Cell Theory
- all living things are composed of one or more cells
- cells are the smallest units of living organisms
- New cells come only from pre-existing cells by cell division
what happens at the end of every life cycle of a somatic cell?
it becomes two cells
What are the three functions of cell division?
- growth of organism
- repair of tissues and organs that have been damaged
- maintenance to replace dying or dead cell
somatic cell definition
body cells of animals
How long does active dividing take (range)?
between 12 to 24 hours
What are the stages of the cell cycle in order?
Interphase
G1
S
G2
Mitosis
early prophase
late prophase (aka prometaphase)
metaphase
anaphase
telophase
cytokinesis
What happens during interphase?
the stage during in which a cell carries out its normal functions. Grows and makes copies of its genetic material in preparation for the next stage of the cycle
What happens in G1 (gap 1)?
major period of growth for a cell, cell synthesizes new molecules and organelles
What happens during S phase (synthesis)?
cellular DNA is copied or replicated
During the S phase, how does DNA exist?
DNA exists during this phase as uncondensed fibres called chromatin
What happens during the G2 phase?
cell has DNA in the form of chromatin which is duplicated but not visible
- there are a pair of centrosomes
- the nucleolus is visible
- the nuclear envelope is present)
What is mitosis?
the stage during which a cell’s nucleus and genetic material divide
What are the 4 phases of mitosis?
early prophase, late prophase, metaphase, anaphase and telophase
What is the result of mitosis?
2 daughter cells that are genetically identical
What happens during prophase?
- the chromatin fibres become more tightly coiled into chromosomes which can be seen with a light microscope
- the nucleoli disappear
- the duplicated chromosomes appear as identical sister chromatids joined at the centromeres
- the centromeres move away from each other
Are the chromatin fibers visible during early prophase?
Yes. They can be seen with a light microscope.
What happens during late prophase?
- the nuclear envelope breaks apart
- spindle fibers made of hollow tub-like structures called microtubules extend from each centrosome and begin to attach contromere of the chromosome
- nonkinetochore microtubules extend to lengthen the cell
What happens during metaphase?
- the spindle fibres guide the chromosomes to the equator of the cell
- The spindle fibers from opposite poles attach to the centromere of each chromosome
- Each pair of sister chromatids is now single chromosome as long as the chromatids remain joined at the centromere
What happens during Anaphase?
During anaphase each centromere
splits apart, and the sister
chromatids separate from each
other.
* The separated sisters chromatids
are now referred to as single
chromosomes.
* The spindle fibres shorten, pulling
the chromosomes to opposite
poles of the cell
What happens during telophase?
- Telophase begins when the
chromosomes have reached opposite
poles of the cell. - The chromosomes start to unwind
into strands of less-visible chromatin. - Spindle fibres break down, the
nuclear membrane forms around the
new set of chromosomes and a
nucleolus forms within each new
nucleus.
What happens during cytokinesis
- the division of the cytoplasm to create two new
daughter cells. - During cytokinesis in animal cells, an indentation forms in
the cell membrane along the equator of the cell - the indentation deepens until the cell is
pinched in two. - The cytoplasm divides equally between the two halves of the cell.
- Cytokinesis ends with the separation of the two genetically identical
daughter cells.
What happens after cytokinesis?
The daughter cells are now in G1 of interphase.
* Other cells complete cell division in different ways.
* Plant cells have a rigid cell wall covering its cell membrane.
Cytokinesis occurs by the formation of a cell plate between the
nuclei.
How many chromosomes and pairs do human somatic cells have?
46 chromosomes and 23 pairs
Within one pair of chromosomes, where is each chromosome from?
one chromosome is from the father and one is from the mother
What are the first 22 pairs called?
autosomes
How many autosome pairs are there?
22
What is the last chromosome pair?
The sex chromosomes
What are the two sex chromosomes?
the X and Y
What sex chromosomes do human females have?
X and X
What sex chromosomes do human males have?
one X and one Y
What are homologous chromosomes?
Homologous chromosomes are pairs of chromosomes that appear similar in terms of their length, centromere location, and banding pattern when stained with certain dyes.
Are homologous pairs identical?
No!
What are genes?
sections of DNA on chromosomes that contain
information for the inheritance of specific traits
How are homologous chromosomes related in the information they carry?
They carry genes for the same traits, such as hair colour, at the same location but they carry different forms of the same gene.
Allele definition
different forms of the same gene
What does the difference in allele shape account for?
The differences in specific traits - brown hair vs blond hair
Karyotype
an individual set of chromosomes that can be photographed
How are karyotypes prepared?
by treating a cell during mitosis to stop division and staining the chromosomes
What happens after the karyotypes are prepared?
They have a banding pattern clearly visible under a light microscope, they are then paired and sorted into homologs of descending size
How are autosomes labelled?
By numbers 1 through 22
