biology sem 1 CAT

Question 1

What is a karyotype?

Answer 1

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.

Question 2

How are chromosomes arranged in a karyotype?

Answer 2

they are arranged in homologous pairs in size order from largest to smallest.

Question 3

How can karyotypes be denoted?

Answer 3

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)

Question 4

Autosomes in human karyotype

Answer 4

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.

Question 5

What is the eukaryotic cell cycle?

Answer 5

the same sequence of events between mitotic divisions.

Question 6

What are the phases of the cell cycle in order?

Answer 6

G1, GO, S, G2 (last 4 make up interphase), M (mitosis), C (cytokinesis).

Question 7

What is meant by haploid?

Answer 7

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.

Question 8

What is meant by diploid?

Answer 8

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.

Question 9

What occurs in the G1 phase?

Answer 9

cell growth before DNA replication. The cell carries out its normal metabolic functions

Question 10

What occurs in the GO phase?

Answer 10

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.

Question 11

What occurs in the S phase?

Answer 11

(Synthesis) DNA is replicated ready for cell division

Question 12

What occurs in the G2 phase?

Answer 12

Cell prepares for division as there is cell growth and the organelles replicate.

Question 13

What occurs in the M phase?

Answer 13

Mitosis (nuclear division) takes place - PMAT

Question 14

What occurs in the C phase?

Answer 14

Cytokinesis - cytoplasmic division takes place where the cell separates into two completely.

Question 15

what is gamete formation?

Answer 15

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.

Question 16

What are the stages of mitosis

Answer 16

Prophase, Metaphase, Anaphase, Telophase (interphase is not really a phase)

Question 17

What happens in interphase?

Answer 17

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.

Question 18

What happens in prophase?

Answer 18

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.

Question 19

What happens in metaphase?

Answer 19

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.

Question 20

What happens in anaphase?

Answer 20

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.

Question 21

What happens in telophase?

Answer 21

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.

Question 22

What are the stages of meiosis?

Answer 22

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.

Question 23

What happens in interphase (meiosis)?

Answer 23

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).

Question 24

What happens in prophase 1?

Answer 24

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.

Question 25

what happens in metaphase 1?

Answer 25

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.

Question 26

What happens in anaphase 1?

Answer 26

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.

Question 27

What happens in telophase 1?

Answer 27

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.

Question 28

What happens in prophase 2?

Answer 28

Chromatin condenses to form visible chromosomes again. New spindle fibres are produced. The nuclear membrane disintegrates.

Question 29

Is there DNA replication before prophase 2?

Answer 29

No

Question 30

what happens in metaphase 2?

Answer 30

Individual chromosomes line up at the metaphase plate/equator. The spindle fibres attach to the sister chromatids at their centromere.

Question 31

What happens in anaphase 2?

Answer 31

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.

Question 32

what happens in telophase 2?

Answer 32

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

Question 33

Why is genetic variation important?

Answer 33

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.

Question 34

How is genetic variation achieved?

Answer 34

Crossing over in prophase 1 and independent assortment in metaphase 2.

Question 35

Why is a thin layer of onion root tip used?

Answer 35

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.

Question 36

Why do you have to stain onion root cells?

Answer 36

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'.

Question 37

why would cells near the root tip be undergoing mitosis?

Answer 37

so that they divide and replicate allowing the number of cells to increase meaning that the organisms grows.

Question 37

Why do new cells grow near the root but not directly at it?

Answer 37

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.

Question 38

Mitosis vs Meiosis : Function

Answer 38

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.

Question 39

Mitosis vs Meiosis: Number of cell divisions?

Answer 39

Mitosis is one and meiosis is two.

Question 40

Mitosis vs Meiosis: type of cell used?

Answer 40

mitosis uses somatic cells and meiosis uses germ cells which form gametes.

Question 40

Mitosis vs Meiosis: Number of chromosomes in daughter cell?

Answer 40

In mitosis it is 46 or diploid (2n), in meiosis each of the 4 non-identical daughter cells contain 23 or haploid (n).

Question 41

Karyotype differences in a person with Down's syndrome?

Answer 41

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.

Question 42

Facial features in a person with Down's syndrome?

Answer 42

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.

Question 43

Intellectual disability in a person with Down's syndrome?

Answer 43

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.

Question 44

What is nondisjunction?

Answer 44

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.

Question 45

Meiosis: Nondisjunction?

Answer 45

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

Question 46

Mitosis : Nondisjunction?

Answer 46

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.