D2.2

Question 1

Consequences of Meiosis

What are Recombinant Chromatids?

Answer 1

• The chromatids thhat end up with unique combinations after crossing occurs between inner chromatids that swap genes and thus contain new combinations of genetic material
• Whole chromatid is a recombinant -> more specifically, specific gene combinations as recombinant

Question 2

Consequences of Meiosis

What is Random Orientation

Answer 2

• Pairs of homologous chromosomes line up next to each other in metaphase I, it is random for EACH chromosome which parental chromosomes goes on which side of metaphase plate.

Question 3

Consequences of Meiosis

What is Non-Disjunction

Answer 3

• Spindle fibres must normally attach to each centromere of the chromatids at the kinetochore to pull them apart
• If one of two doesn’t have an attached spindle fibre they will NOT separate and both will go to one side.
• Can occur in Anaphase I or Anaphase II
• Creates abnormal gametes

Question 4

Consequences of Meiosis

How can Crossing over create Genetic Variation?

Answer 4

• Crossing over creates New COMBINATIONS of alleles, not new alleles themself.
• New combinations can create new phenotypic variation <— source of genetic variation.

Question 5

Consequences of Meiosis

How does Random orientation create Genetic Variation?

Answer 5

• Random orientation alters the combinations of alleles inherited, without directly changing alleles.
• Changing combinations creates more unique offspring resulting in genetic variation in a population
• A reason for Mendel’s laws of inheritance.

Question 6

Consequences of Meiosis

How is Meiosis related to Natural Selection?

Answer 6

• Crossing over & Random orientation occur in meiosis –> can create new combinations of alleles, and thus give rise to new phenotypes.
• New variration is first step in natural selection

Question 7

Consequences of Meiosis

What is the cause and the characteristics of Down Syndrome?

Answer 7

• The result of non-disjunction of Chromosome 21
• The non-disjunction causes a gamete to have 2 copies of chromosome 21 and if fertilized, the zygote has three copies (trisomy) of chromosome 21 (often not coompatible with life)

Question 8

Consequences of Meiosis

What happens with Non-Disjunction as Materal age increases?

Answer 8

• During prime fertility windows –> body prioritises correct spindle alignment to prevent non-disjunction
• With age, there is less priority for checking so errors can go unchecked/more gametes contain errors.
• Results in an increase in miscarriage rates & live births of children with Down Syndrome

Question 9

Cell Cycle Regulation and Cancer

What are Cyclins and the Cyclin-Dependent Kinases?

Answer 9

• Cylins are proteins controlling whether a cell will progress through cycle.
• Does so by binding the enzymes, Cyclin-Dependent Kinases, which when not bound, is inactive and unable to accelerate the next phase of cell cycle
• When cyclin binds, enzymes activate, causes advancement of cell.

Question 10

Cell Cycle Regulation and Cancer

What are checkpoints in the Cell Cycle?

Answer 10

• Where events stall until certain requirements have been met for it continue.
• Progression through checkpoints is regulated with cyclin levels
• Increasing cyclin levels Can allow cell to proceed through checkpoint.

Question 11

Cell Cycle Regulation and Cancer

What are Cancer Cells?

Answer 11

• Cell that undergo extremely rapid and uncontrolled reproduction with very little differentiation
• Results in mass of cells not performing its noraml useful function

Question 12

Cell Cycle Regulation and Cancer

What are Proto-oncogenes?

Answer 12

• A gene that stimulates or causes cell division, when expressed, cells divide.
• If not mutated and functioning properly, called proto-oncogenes.
• If a mutation occurs, it can cause too much stimulation of cell division which is called an oncogene

Question 13

Cell Cycle Regulation and Cancer

What are Tumour-Suppressor Genes

Answer 13

• Codes for proteins that play a role in slowing, pausing or stopping the cell cycle & cell division/ in repairing DNA damage
• Genes, when functioning, prevent tumours forming

Question 14

Cell Cycle Regulation and Cancer

What does it mean for a tumour to be benign?

Answer 14

• Contained in a single part of the body and is not spreading
• Can be medically removed
• Still technically a type of cancer cell

Question 15

Cell Cycle Regulation and Cancer

What is Metastasis?

Answer 15

• Cells form a primary tumour then break off and enter the bloodstream/vascularised
• Cells travel via blood to new location and start growing new tumour

Question 16

Cell Cycle Regulation and Cancer

What is the significance of G0?

Not techincally in the cell cycle

Answer 16

• Not all cells should be dividing
• Most actually leave the G1 zone once they’ve grown to full functional size and enter G0
• They don’t replicate DNA or progress through the cycle, just perform noraml functions

Question 17

Cell Cycle Regulation and Cancer

How does a Proto-oncogene mutation form a tumour?

Acceleration

Answer 17

• If onocogenes become mutated, can start to promote cell division when its NOT appropriate/absence of checkpoints
• Leads to over promotion of division, creating a tumour

Question 18

Cell Cycle Regulation and Cancer

How can a mutation in the tumour suppressor gene cause a tumour to form?

No breaks

Answer 18

• Normally, tumour supressor genes inhibit & pause cell division
• IF mutation occurs, the ability to stop cell division is compromised and tumours form as a result

Question 19

Cell Cycle Regulation and Cancer

Compare Primary vs Secondary Tumours

Answer 19

• PRIMARY: First cluster of cancerous cells, forming as a result of mutation in an oncogene/tumour-suppresor gene
• SECONDARY: The primary tumour can become vascularised, then metastasize (spread through body) –> forms new tumour, the secondary tumour.

Question 20

Regulation of Gene Expression

Gene Regulation?

Answer 20

• Process of controlling the timing, location and amount in which genes are expressed in an organism
• Leads to cell specialisatoin in multicellular organsms
• Allows cell to be responsive to environments

Question 21

Regulation of Gene Expression

What is a phenotype?

Answer 21

• The physical trait that is the result of the specific proteins that the individual has - result of their expressed genes
• Genotype is related to the gene that it has, its transcriptone relates the different mRNAs formed
• The proteome (relates to proteins it makes) causes the phenotype.

Question 22

Regulation of Gene Expression

mRNA degradation?

Regulates how often an mRNA is translated

Answer 22

• The use of enzymes to break up the mRNA to nucleotides for recycling
• Removes the poly A tail, GTP cap and then breaks bonds between nucleotides.

Question 23

Regulation of Gene Expression

What are exonucleases?

- ases (ENZYME)

Answer 23

• Enzymes that break down nuclei acids by removing individual nucleotides
• If used for mRNA degeadation, requires the decapping enzyme that breaks poly A tail and exonucleases that remove nucleotides from the 3’ OR 5’ end

Question 24

Regulation of Gene Expression

What is epigenesis?

Answer 24

• Refers to the pattern of gene expression that causes cells to utilise parts of their genome to become specialised
• Process of changing the phenotype of a cell without changing the genotype, driven by internal signalling messages and external environmental cures.

Question 25

# Regulation of Gene Expression What are Epigenetic tags?

Answer 25

* Chemical modficiations to the DNA to **flag part of the genome to GUIDE its regulation** * Can signal a gene to be expressed or a single gene to be 'turned off' * E.g., **Methly groups** that SILENCE genes.

Question 26

# Regulation of Gene Expression What is DNA Methylation

Answer 26

* The process of adding a CH3 methly group to a **DNA nucleotide** as an **epigenetic tag** * Methly groups are often added to the **promoter** region to **block transcription factors**, thereby silencing the gene/ prevent its expression.

Question 27

# Regulation of Gene Expression What is the significance of the Promoter? | Like the 'light-switch' of the gene

Answer 27

* A region **ahead of coding bases**, is the binding site for transcription factors which then **allow RNA polymerase** to bind * They indicate where each new genes begins

Question 28

# Regulation of Gene Expression What is the significance of transcription facotrs?

Answer 28

* They're proteins that **regulate transcription**, can be through a single gene or genes. * Can act as **activators** which bind and increase the likelihood/rate of transcription, or can act as **silencers** that block/reduce transcription.

Question 29

# Regulation of Gene Expression What is the significance of enhancer regions?

Answer 29

* They have binding sites for **activators to bind to** * When activators, a type of transcription factor, bind, the **DNA forms a loop** allowing the activators to interact with transcription factors at the promoter, **increasing the rate of transcription.**

Question 30

# Regulation of Gene Expression How is transcription initiated and prevented?

Answer 30

* **INITIATED**: The transcription factors that accelerate or promote transcription are called **activators** and they bind to **enhancers**. * **PREVENTED**: Transcriptions factors that prevent transcription are called **repressors** and they bind to **silencers**

Question 31

# Regulation of Gene Expression How is the length of the Poly A tail regulated? | Regulation of TRANSLATION

Answer 31

* Altering the length of poly A tail/ speed of poly A degredation can regulate translation * **Enzymes degrade the tail by breaking off** * Longer tails take more time before mRNA gets broken down, so more protein made * **EXTERNAL signals/chemicals** can also accelerate rate of degredation to remove mRNA when protein not needed.

Question 32

# Regulation of Gene Expression How is DNA methylation a form of regulating TRANSCRIPTION?

Answer 32

* Methylation, particularly at the **promoter**, can turn off expression of a gene by disallowing the **binding of necessary transcription factors** * Can occur during the lifetime and be brought on by **envrionmental factors** * Methy groups can also bind to the **histone proteins that DNA wraps around** to block a section of genes

Question 33

# Epigenetic Inheritance What is Epigenetic Inheritance?

Answer 33

* Events that occur during one's lifetime **cause epigenetic tags** * In **MITOSIS**, those tags are **passed down** along so that the specialised cells formed are identical - passed to offspring. * Impact of environmental experiences can be passed along this way.

Question 34

# Epigenetic Inheritance What are Primordial germ cells?

Answer 34

* **Diploid germ cells** that will go through **MEIOSIS** to form gametes. * The PGCs are formed before the organism is born and have MOST of the **epigenetic tags removed**

Question 35

# Epigenetic Inheritance What is epigenetic reprogramming?

Answer 35

* The process of **removing epigenetic tags during the formation fo primordial germ cells** * Important to that a zygote can form with access to full genome - epigenetic tags reprogrammed/added to zygote to drive its development of specialised cells and tissues.

Question 36

# Epigenetic Inheritance What are Imprinted Genes?

Answer 36

* When a gene is silenced in **only one type of gamete** (e.g., silenced in sperm but expressed in eggs). * They bypass mendelian inheritance patterns based on **two copies of each gene** * *Exempler Genetic disorders*: Angelman Syndrome and Prader-Willi

Question 37

# Epigenetic Inheritance What are differentially methlayed regions? | Think of Identical Twins

Answer 37

* Although indentical twins have the exact same DNA base sequence, they don't have the same **gene EXPRESSION** becayse they acucmulate **different methylation patterns** during their lifetime. * Can study epigenetic impact through identical twins with varying methylation patterns to see if there's correlation between these regions and different **phenotypic outcomes for the twins**

Question 38

# Epigenetic Inheritance What is an operon?

Answer 38

* An operon is a unit of genetic material containing **multiple genes and regulatory sequences** * In **prokaryotes** several genes can share a single promotor, enabling groups of genes to be turned on & off together when sharing a function. * This is done using an **operator** sight next to the promtor that a **repressor either binds to or not**/ a specific DNA sequence within the operon that acts as a control switch.

Question 39

# Epigenetic Inheritance What is the role of the environment for epigenetic tagging?

Answer 39

* Environmental stresses can alter the **formation of epigenetic tags** * Can be a way of changing gene expression to potimize coping with extreme external stressors, potentially leading to problems associated with **altering baseline expression** * E.g., - **Air pollution**

Question 40

# Epigenetic Inheritance How is Air pollution and Methylation related?

Answer 40

* Chemicals in air polluation (nitrous oxide, hydrocarbons) have been shown to **decrease DNA mathylation across genome** * Causes **more expression of proteins** that regulate the immune system. * Increased expression of this is linked to asthma, heart disease & inflammation. * Can be be more signficiant for pregnant women - offspring since PGCs are forming them.

Question 41

# Epigenetic Inheritance Explain epigenetic inheritance in ligers and tigeons.

Answer 41

* **MALE pattern of imprinting** favours the **larger** offspring. * **FEMALE** patterns favour the **smaller** offspring. * BUT, when mated with tiger to make a hybrid, gender matters. * **Male lions** form large ligers * **Female lions** form small tigeons

Question 42

# Epigenetic Inheritance Discuss the relationship between methylation and monozygotic tiwns.

Answer 42

* Despite having **identical DNA sequences**, identical twins can have different phenotypes. * Their methylation patterns provide insight into the process of DNA methylation & its role in phenotype. * **Methylation** patterns have a genetic basis but are **influnced by environment**

Question 43

# Epigenetic Inheritance What is the role of insulin in regulating gene expression? | Think glucose

Answer 43

* Glucose in blood triggers the **transcription of INS** insulin gene. * The amount of glucose in the environment thus triggers the expresison of genes related to the hormone.

Question 44

# Epigenetic Inheritance How does the Lac Operon regulate lactose? | In PROKARYOTES

Answer 44

* Regulates lactose by using a **repressor protein** that is either on or off, controlled by the **presence of lactose**. * When lactose is absent, **repressor protein binds to the operator**, blocking RNA polymerase and preventing transcription of genes needed for lactose metabolism. * When lactose is present, it **BINDS to the repressor**, causing a **shape change** so it can no longer block the operator, allowing RNA polymerase to **transcribe** the genes and produce the **enzymes needed to break down lactose.**