1.6: Cell Division Flashcards
What is the structure of chromosomes?
In each cell there are pairs of
chromosomes – one inherited
from each parent. They
contain the same genes e.g.
the gene for hair colour 2
chromosomes that carry the
same genes at the same
position are called
HOMOLOGOUS
CHROMOSOMES
What does each chromosome contain?
one molecule of DNA, which includes genes.
What must daughter cells produced through the cell cycle contain?
A copy of all instructions for the cell, which includes a full set of chromosomes, which are exactly copied from the parent cell.
What are molecules of DNA wrapped around in eukaryotes?
proteins called histones
What is chromatin?
the DNA and histone proteins together
What must happen before a cell is replicated?
copies of the DNA must be made
What are two replica strands also called?
sister chromatids
What are the sister chromatids held together by?
A centromere
How many chromosomes are there in:
- humans
- onion cells
- chimpanzees
- dogs
humans: 46
onion cells: 12
Chimpanzees: 48
Dogs: 78
What is asexual reproduction?
production of a new individual of a species by one parent organism- eg. yeast, Amoeba.
What is vegetative propagation?
in multi cellular organisms, a new individual can bud off the parent and grow in a new plant.
What does sexual reproduction involve?
fusing of 2 nuclei from 2 different individuals to produce offspring
What is a gamete?
Where each cell has given half the genetic information – half the number of chromosomes.
What is meiosis?
the type of cell division responsible for the formation of gametes (takes place in sex organs)
What does every normal cell in the body contain?
homologous pairs of chromosomes (diploid cells)
What happens in the reproductive organs during sexual reproduction?
the pairs separate and one chromosome goes to each of the daughter cells. The gametes are haploid
What is the biological significance of mitosis?
- Production of genetically identical cells
- Replacement of cells and repair of tissue.
- Growth – every cell in your body is derived from one cell, the zygote, which was formed when 2 gametes fused. This then continues to divide until a multicellular organism is produced.
When does DNA molecule replication occur in mitosis?
Interphase
What is the resting phase in mitosis?
chromosomes are not visible. This is a period of considerable metabolic activity in the cell. DNA content of the cell is doubling. Duplication of cell organelles is also taking place.
What are the four stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
What occurs in prophase in mitosis?
- Chromosomes shorten and thicken and become visible. They comprise of 2 chromatids joined at the centromere.
- Centrioles in the cytoplasm migrate to the poles. From each centriole develops spindle fibres made of microtubules. The nucleolus disappears. By the end of prophase the nuclear membrane has disintegrated.
What occurs in the metaphase?
Chromosomes arrange themselves at the equator of the spindle and becomes attached to the spindle fibres at the centromere. The fibres begin to contract pulling the chromatids slightly apart.
What occurs in the anaphase in mitosis?
Spindle fibres shorten causing the 2 chromatids to separate and migrate towards opposite poles, centromere first. Energy for contraction is provided by mitochondria (ATP).
What occurs in the telophase in mitosis?
Chromatids arrive at the poles. A new nuclear envelope forms round them. Chromatids uncoil and become invisible. Spindle fibres disintegrate and the nucleolus reforms in each new nucleus.
What happens ONLY in animals in terms of mitosis?
constriction of the cell begins as the cell divides.
Cell division, or cytokinesis, then takes place.
What does the cell cycle look like?
What is the interphase stage in meiosis?
- dna replicates
- centrioles replicate
What occurs in early prophase I (meiosis)
- Chromosomes shorten and thicken & become visible
- They are made of 2 identical sister chromatids joined by a centromere
- Nuclear envelope breaks down
- Centrioles move to poles
What occurs in Mid prophase I (meiosis)?
Each homologous pair of chromosomes comes together to form a bivalent. This is called synapsis
What occurs in the late prophase I?
Chromatids from homologous chromosomes cross over at points called chiasmata and sections of chromatids are swapped
What occurs in metaphase I?
- Bivalents arrange themselves on the equator (middle) of the spindle
- Independent/random assortment
- They are attached to the spindle fibres by their centromeres
What occurs in Anaphase I?
Homologous pairs of chromosomes separate and 1 of each pair (bivalent) are pulled by the spindle fibres towards the poles
What occurs in telephase I?
- Cells divide and nuclear envelope and nucleolus reforms
- This stage doesn’t occur in plants they go straight to metaphase II
What occurs in prophase II?
- Nuclear envelope breaks down & nucleolus disappears
- Centrioles replicate and move to opposite poles
- Chromosomes shorten and thicken and spindle re-forms at right angles to the original spindle
What occurs in Metaphase II?
Chromosomes arrange themselves across the middle (equator) of the cell
What occurs in Anaphase II?
Centromeres divide and chromatids are pulled towards the opposite poles (centromere first) by the spindle fibres
What occurs in telophase II?
Nuclear envelope and nucleolus reforms
What occurs in cytokinesis?
- Cell division
- Tetrad of 4 haploid cells with half the number of chromosomes of the parent
What are diploid cells?
cells that contain two pairs of each type of chromosome, one maternal and one paternal. Two sets of chromosomes is indicated by the symbol 2n.
What are haploid cells?
Haploid cells contain one set of chromosomes. This one set is indicated by the symbol n.
Comparison between mitosis and meiosis?
chromosome number
mitosis: 2n two sets of chromosomes
meiosis: n- one set if chromosomes
Comparison between mitosis and meiosis?
policy
mitosis: Diploid
Meiosis: Haploid
Comparison between mitosis and meiosis?
Outcome of process
Mitosis: Genetically identical daughter cells
Meiosis: Genetically different daughter cells
Comparison between mitosis and meiosis?
Type of cells produced
Mitosis: Normal body cells
Meiosis: Gametes
Cancer facts:
- how many deaths due to cancer?
- How many deaths due to lung cancer?
- Most common cancer in men/women
- How many different forms?
- 1 in 4 deaths
- 1 in 17 due to lung cancer
- most common in men: lung cancer
- most common in women: Breast cancer
- over 100 different forms of cancer
How does cancer work?
Cancerous cells divide repeatedly out of control even though they are not needed, they crowd out other normal cells and function abnormally. They can also destroy the correct functioning of major organs.
What causes cancer?
- Cancer arises from the mutation of a normal gene.
- Mutated genes that cause cancer are called oncogenes.
- It is thought that several mutations need to occur to give rise to cancer
- Cells that are old or not functioning properly normally self destruct and are replaced by new cells.
- However, cancerous cells do not self destruct and continue to divide rapidly producing millions of new cancerous cells.
What is cancer?
- uncontrolled cell division by mitosis
- which causes a tumour to form
What is a mutagen?
A factor which brings about a mutation
What is an oncogene?
mutated genes that cause cancer
What is a carcinogen?
An agent that causes cancer, described as carcinogenic
What are examples of carcinogens?
- Ionising radiation – X Rays, UV light
- Chemicals – tar from cigarettes
- Virus infection – papilloma virus can be responsible for cervical cancer.
- Hereditary predisposition – Some families are more susceptible to getting certain cancers. Remember you can’t inherit cancer it’s just that you maybe more susceptible to getting it.
