biology sem 1 CAT Flashcards
What is a karyotype?
a photograph of the chromosomes in a cell that is used to check for abnormalities.
They are prepared by staining the chromosomes with dye and photographing them through a microscope.
How are chromosomes arranged in a karyotype?
they are arranged in homologous pairs in size order from largest to smallest.
How can karyotypes be denoted?
Where the first number is the number of chromosomes and then the second two digits are either XX or XY depending on what the gender is (male or female respectively)
Autosomes in human karyotype
Within a karyotype eg for humans there are 23 pairs of chromosomes. Within that 22 pairs are autosomes meaning that they contain DNA and genes and then the other pair are of the sex chromosomes that depict gender.
What is the eukaryotic cell cycle?
the same sequence of events between mitotic divisions.
What are the phases of the cell cycle in order?
G1, GO, S, G2 (last 4 make up interphase), M (mitosis), C (cytokinesis).
What is meant by haploid?
A haploid denoted by n are cells that contain a single set of chromosomes, in which there is only one member of the pair. In humans the only haploids are the sperm and egg cells which contain 23 single chromosomes.
What is meant by diploid?
A diploid denoted by 2n are cells which contain a complete sets of chromosomes with each parents contributing one chromosome out of the pair of two. In humans all somatic cells are diploids and contain 46 chromosomes, 23 from male, 23 from female with one male and one female one pairing up to create homologous pairs.
What occurs in the G1 phase?
cell growth before DNA replication. The cell carries out its normal metabolic functions
What occurs in the GO phase?
a resting phase for cells. A cell may remain there for its lifetime or only temporary. Stem cells also wait here for replication, and then when called upon they come out of it and continue to life cycle.
What occurs in the S phase?
(Synthesis) DNA is replicated ready for cell division
What occurs in the G2 phase?
Cell prepares for division as there is cell growth and the organelles replicate.
What occurs in the M phase?
Mitosis (nuclear division) takes place - PMAT
What occurs in the C phase?
Cytokinesis - cytoplasmic division takes place where the cell separates into two completely.
what is gamete formation?
Genetically unique gametes are formed through meiosis where only one chromosome from each homologous pair in the parent cell is copied to the gamete. It begins with a germ cell and end with 4 unique haploid gamete cells.
What are the stages of mitosis
Prophase, Metaphase, Anaphase, Telophase (interphase is not really a phase)
What happens in interphase?
At this point the chromosomes are unravelled and exist as chromatin. These 46 chromatin pieces replicate so that there are 46 pairs of chromatin pieces - in this pair both are identical copies of each other. The organelles of the cells also replicate including the centrioles. The cells also increase in size.
What happens in prophase?
The DNA collects together and coils around the histones so that they are in the shape of chromosomes which are visible. The two pairs of centrioles also become visible and move to either pole of the cell. The nuclear membrane breaks down so chromosomes are let loose and the nucleolus disappears. The spindle fibres or microtubules are formed from the centrioles.
What happens in metaphase?
The chromosomes are really distinctively visible in their shape. The chromosomes attach onto the spindle fibres and the microtubules tug and pull of the chromosomes until they are perfectly line dup at the equator of the cell or the metaphase plate.
What happens in anaphase?
The spindle fibres pull of the chromosomes so that the two chromatids are separated and they are pulled opposite ways to either pole of the cell. The chromatids are now called chromosomes. It is the shortest phase of mitosis.
What happens in telophase?
Two sets of chromosomes form groups at each pole. The DNA packages together into the nuclear membrane which is reformed and the chromosomes uncoil back into chromatin hence as soon as telophase is over you can’t see the shape of the chromosomes. The nucleolus returns. At the same time cytokinesis occurs so that the cleavage furrow is formed in the cell where the cell is dividing. The cleavage depends until the cytoplasm is split into two separate daughter cells.
What are the stages of meiosis?
There is meiosis 1 consisting of IPMAT which produces 2 haploid daughter cells with 46 chromatids and meiosis 2 consisting of PMAT which produces 4 daughter cells with 23 chromatids.
What happens in interphase (meiosis)?
You begin with a germ cell that is diploid and has 46 chromatids. DNA replication occurs where 46 chromatids become 92. These 46 double chromosomes are sister chromosomes meaning they are identical to each other. The cell grows in size. All organelles are replicated (roughly 4 times so that there is sufficient amount for the 4 daughter cells produced at the end).
What happens in prophase 1?
The DNA condenses into chromosomes. Maternal chromosomes are attracted to paternal chromosomes and vice versa they are called homologues or homologous pairs. Once attracted they join and crossing over occurs. The nuclear membrane disintegrates and the nucleolus disappears. Centrioles move to opposite ends of the cell and the meiotic spindle beings to form.
what happens in metaphase 1?
The chromosomes line up at the equator/metaphase plate of the cell still in their homologous pairs. Lining up is independent assortment as the pairs are lined up on one side or the other independent of each other. The chromosomes are attached to the spindle fibres which move them into place.
What happens in anaphase 1?
The spindle fibres shorten, pulling on the centromere of each chromosomes. This separates the homologous pairs yet sister chromatids remain with each other and are pulled to either end of the cell.
What happens in telophase 1?
New nuclear membrane forms and chromosomes unravel into chromatin. The spindle fibres disintegrate. Two daughter cells are formed which have 23 duplicated chromosomes that are not homologuos meaning that the cell is haploid as it doesn’t have a full set of chromosomes.
What happens in prophase 2?
Chromatin condenses to form visible chromosomes again. New spindle fibres are produced. The nuclear membrane disintegrates.
Is there DNA replication before prophase 2?
No
what happens in metaphase 2?
Individual chromosomes line up at the metaphase plate/equator. The spindle fibres attach to the sister chromatids at their centromere.
What happens in anaphase 2?
The centromeres of each chromosome disconnect allowing sister chromatids to separate. The spindle fibres shorten pulling the chromatids apart to either end of the cell. In an animal cell the cleavage furrow beings to form and in plant cells a cell wall forms.
what happens in telophase 2?
chromosomes unwind, loosen and reform chromatin. 4 new nuclear membranes form around the nuclei one in each new daughter cell. The cells separate into 4 new non-identical haploid daughter cells
Why is genetic variation important?
it ensures natural variation within a species. This is because every gamete produced is different to the others meaning that every combination is new and unique. Creating genetic diversity is vital to a species survival as it allows them to adapt to the changing environment around them.
How is genetic variation achieved?
Crossing over in prophase 1 and independent assortment in metaphase 2.
Why is a thin layer of onion root tip used?
so that it is transparent and not opaque and therefore light can pass through layer of onion cells and can be seen when looking down the microscope.
Why do you have to stain onion root cells?
you can enhance the visibility of all the different structures and you can see the different cell walls and identify different cells and also so that you can see their nucleus’.
why would cells near the root tip be undergoing mitosis?
so that they divide and replicate allowing the number of cells to increase meaning that the organisms grows.
Why do new cells grow near the root but not directly at it?
any new cells that are created are very delicate and soft and can be easily damaged whilst having mature strong cells in front of it allows the new cells to push them through the soil and be protected by these mature cells.
Mitosis vs Meiosis : Function
In mitosis the purpose is to create two identical copies of a cell by nuclear and cellular division for growth, repair and asexual reproduction. The purpose of nuclear and cellular division for producing gametes.
Mitosis vs Meiosis: Number of cell divisions?
Mitosis is one and meiosis is two.
Mitosis vs Meiosis: type of cell used?
mitosis uses somatic cells and meiosis uses germ cells which form gametes.
Mitosis vs Meiosis: Number of chromosomes in daughter cell?
In mitosis it is 46 or diploid (2n), in meiosis each of the 4 non-identical daughter cells contain 23 or haploid (n).
Karyotype differences in a person with Down’s syndrome?
A person with down’s syndrome has an extra copy of chromosomes 21, meaning that in a cell it has 3 copies of chromosomes 21 instead of 2. This means in a cell it would have 47 chromosomes, compared to 46 in a normal cell.
Facial features in a person with Down’s syndrome?
cause different facial features in individuals with drown syndrome such as a flattened face (especially the bridge of the nose) and almond shaped eyes that slant up.
Intellectual disability in a person with Down’s syndrome?
Individuals with down syndrome can also face intellectual disagrees although the degree to which can vary. Generally children reach key developmental milestones later than toher children eg walking and talking and they may experience challenges with attention span, verbal memory and expressive communication, all making it hard to learn. They may also face behavioural problems such as stubbornness, impulsivity and temper tantrums.
What is nondisjunction?
Nondisjunction occurs during anaphase and it is when chromosomes do not split equally meaning that the amount of chromosomes at each pole of the cell is unequal. This means that when the cells divides a cell may have an extra chromosomes or one chromosomes less than it should.
Meiosis: Nondisjunction?
Nondisjunction is what causes Down’s syndrome. When it occurs in meiosis it means that the gamete has an extra chromosomes 21. Then the gametes fertilise each other and all cells in the zygote has an extra chromosome 21. Meaning that after cell division all cells in the individual would have an extra chromosome 21 leading to a full trisomy 21 or complete Down’s syndrome
Mitosis : Nondisjunction?
if nondisjunction were to occur during mitosis it would occur during the early stages of the embryo. Due to the fact that different cells are dividing and replication only the ones with the nondisjunction would produce cells with an extra chromosome 21. This means that some cells may have the abnormality and other cells wouldn’t which leads to mosaic down syndrome where only some cells are affected and the symptoms of it are far less severe than full down syndrome.
