Chromosome Inheritance Session 18

Question 1

What are chromatins?

Answer 1

• It is the the DNA and the protein collectively in the chromosome

Question 2

How many chromosomes are there in the human body and what are the two different types ?

Answer 2

• There are 46 chromosomes /23 pairs
• 22 of them are called autosomes : which are found in both male and female
• 1 pair consists in sex chromosomes because they contain genes that control gender (X and Y)

Question 3

What are the chromosomes male and females have ? ( X or Y)

Answer 3

• Males : XY
• Females :XX

Question 4

What gene does the Y chromosome have and what does it help with ?

Answer 4

• It has the SRY gene that causes testes to develop

Question 5

What are Karyotypes ?

Answer 5

• It is an artificial display of the chromosomes present in a cell during metaphase

Question 6

What does the Centromere do ?

Answer 6

• It holds together the chromatids until a certain phase of mitosis , when the centromere splits

Question 7

What are the two phases of the cell cycle ?

Answer 7

• Interphase and a Division Phase

Question 8

What are the the 3 different phases during interphase and what happens in each of them ?

Answer 8

• G1 stage : the cell performs its normal functions and doubles its organelle and accumulates the materials needed for DNA synthesis
• S Stage: DNA replication happens and after this stage there are two identical sister chromatids
• G2 stage : synthesizes the proteins needed for cell division

Question 9

If a cell never enters the S and G2 stages and are permanently arrested in G1 , what stage are they known to be in and name two types of cells that go through this process

Answer 9

• Nerve and muscle cells
• they are known to be in the G0 stage

Question 10

What are the two stages that occur within Cell division (M phase) and what occurs within each of them ?

Answer 10

• Mitosis : a type of nuclear division , also known as duplication division since each new nucleus contains the same number and type of chromosomes as the former cell
• Cytokinesis : Division of cytoplasm

Question 11

How is mitosis balanced out to keep it running continuously , what happens with the cells that are no longer needed after mitosis or have been excessively damaged ?

Answer 11

• Apoptosis occurs which is programmed cell death

Question 12

How is the cell cycle controlled to ensure the conditions of each step is met ?

Answer 12

• By checkpoints at different stages of the cycle to ensure conditions are met

Question 13

What are the 3 different checkpoints in the Cell Cycle ?

Answer 13

• G1, G2 and M checkpoint

Question 14

What occurs during the G1 checkpoint ?

Answer 14

• Cells are checked here if they are capable of passing through and if they don’t pass through, they are sent to G0 , where they continue to perform normal functions but do not divide
• the integrity of DNA is also checked , if it is damaged , proteins such as p53 stop the cycle and place the cell in G0 , if they can be repaired , they can renter the cycle but if not they undergo apoptosis

Question 15

What occurs in the G2 checkpoint ?

Answer 15

• The cell cycle is paused here to ensure that the DNA has replicated. If DNA is damaged , then it can be repaired here so it isn’t passed on to the daughter cells

Question 16

What occurs at (M) Mitotic checkpoints and where does it occur ?

Answer 16

• It occurs between Metaphase and Anaphase
• it ensures that chromosomes are properly attached to the spindle so they can be distributed accurately to the daughter cells

Question 17

What are some external controls of the cell division?

Answer 17

• hormone or growth factor can stimulate a cell to divide

Question 18

What is the signal transduction pathway ?

Answer 18

• It is a pathway formed by proteins that pass the signal from one to the next

Question 19

What do the genes , proto-oncogenes and tumour suppressor genes do ?

Answer 19

• Proto-oncogenes stimulate the cell cycle
• Tumor supressor genes inhibit the cell cycle

Question 20

What are cyclins and what do they do ?

Answer 20

• They are a family of regulatory proteins that control the progression of the cell cycle

Question 21

What are the different stages of mitosis ?

Answer 21

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase

Question 22

What is an Aster ?

Answer 22

• An array of microtubules

Question 23

What does each centromere contain ?

Answer 23

• a pair of centrioles , which consist of short cylinders of microtubules (9 triplets).

Question 24

What occurs during the prophase ?

Answer 24

• The centrosomes have duplicate (during early S phase ) , they move towards opposite ends of nucleus
• Spindle fibers appear
• Nuclear envelop begins to fragment
• the nucleolus disappears
• chromosomes condense and are now visible

Question 25

What occurs during Prometaphase ?

Answer 25

• The spindle fibres attach to the centromeres as the chromosomes continue to shorten and thicken
• 46 chromosomes start moving toward middle of the cell

Question 26

What occurs at metaphase ?

Answer 26

• Chromosomes attached to the spindle fibres line up at the metaphase plate

Question 27

What occurs during Anaphase ?

Answer 27

• Centromeres divide , the sister chromatids separate and move toward opposite poles of the spindle

Question 28

What occurs during telophase ?

Answer 28

• this only begins when chromosomes arrive at the poles
• chromosomes become indistinct chromatin again
• Spindle disappears
• nuclear envelope reappears
• nucleolus reappears

Question 29

What occurs during cytokinesis ?

Answer 29

• division of the cytoplasm and organelle occur (not part of mitosis )
• an indentation called a cleavage furrow passes around the circumference of the cell.

Question 30

How does the cleavage furrow occur ?

Answer 30

• Actin filaments form a contractile ring , then as the ring becomes smaller , the cleavage furrow pieces the cell in half