Genetics Of Living Systems C19 + C20

Question 1

Gene mutation

Answer 1

Random unpredictable change in DNA effecting just 1 small part of a DNA molecule

Question 2

Chromosome mutation

Answer 2

Random unpredictable change in DNA effecting large pieces of chromosome or even the number of chromosomes present

Question 3

Types of gene mutation

Answer 3

Substitution insertion deletion

Question 4

Point mutation - substitution

Answer 4

When one base get replaced for another
Likely to add a different AA to polypeptide chain causing it to fold and interact differently ( tertiary and quaternary structure)
May have no effect due to genetic code being degenerate ( more than 1 codon codes for the same AA)
Different AA may have similar properties to the AA that was meant to be translated, therefore interactions may not be different

Question 5

Point mutation insertion and deletion

Answer 5

Addition or deletion of one bass from the sequence meaning whole sequence from after that point is effected as codes are read in 3’s, each 3 is effected coding for a different AA each time
This is known as a frame shift

Question 6

4 stages at which gene expression can be controlled

Answer 6

Transcriptional control
Post transcriptional control
Translation control
Post translation control

Question 7

4 types of transcriptional control

Answer 7

Transcription factors
Chromatin remodelling
Methylation
Acetylation

Question 8

Transcription factors (transcriptional control)

Answer 8

Proteins that bind to specific DNA sequences ( promoter regions)
complex of transcription factors are required for transcription to begin
By increasing/decreasing the production of specific transcription factors transcription of other genes can be controlled

Question 9

Chromatin remodelling (transcriptional control)

Answer 9

In Eukaryotes DNA is associated with histone proteins, forming chromatin
The DNA wraps twice around a bundle of 8 histones to form a chromatin subunit structure called a nucleosome

Question 10

Methylation (transcriptional control)

Answer 10

Addition of ME groups to DNA causes it to be more tightly packed as a result transcription factors cannot bind to the DNA and genes are not expressed

Question 11

Acetylation and phosphorylation transcriptional control)

Answer 11

Reduce the positive charge on the histones resulting in looser packing therefore transcription factors can bind to DNA expressing genes

Question 12

The lac operon ( transcriptional control) in ecoli a prokaryote

Answer 12

DNA strand is made up of regulatory gene, gap, promoter , operator , structural genes
DNA strand codes for lactose permease and lactase
repressor molecule binds to the promoter region stopping transcription
When lactose is present it binds to the repressor causing it to unbind from the dna allowing transcription to occur

Question 13

Exon and intron

Answer 13

Exon - EXpressed region of DNA

intron- interagenic region ( region within the gene)

Question 14

Post transcriptional control

Answer 14

Transcription produces a molecule called pre-mRNA which must be processed to form mature mRNA.
A cap and a tail are added, while splicing by spliceosomes removes introns
Some mRNA can also be edited through addition, deletion, or substitution
These modifications mean that a single length of DNA can produce a range of different strands of mRNA

Question 15

Translation control

Answer 15

Degradation of mRNA - the more resistant the molecule the longer it will last in the cytoplasm, meaning a greater quantity of protein synthesis
Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins
Activation of initiation factors which aid the binding of mRNA to ribosomes

Question 16

Protein kinases

Answer 16

Are enzymes that catalase the addition of phosphate groups to proteins
Addition of phosphate groups changes the tertiary structure and therefore the function of the protein
Many enzymes are activated by phosphorylation making protein kinases important regulators of cell activity
Protein kinases are often activated by the secondary messenger cAMP

Question 17

Post translation control

Answer 17

Involves modification to the proteins that have been synthesised

Question 18

What is morphogenesis

Answer 18

Regulation of the pattern of anatomical development, is controlled by a specific group of regulatory genes called homeobox genes

Question 19

What are homeobox genes

Answer 19

ancient highly conserved regions of dna found in plants, animals and fungi that regulate morphogenesis.
Always 180 base pairs long
Code for home domains- protein segments (60 amino acids) that are transcription factors
Therefore are able to switch other genes on or off, in doing so they control the development of the body plan
Their activity is absolutely fundamental to the development of the body plan

Question 20

Hox genes

Answer 20

Specific group of homeobox genes that are only found in animals
Responsible for positioning of body parts
Highly conserved across great evolutionary distances
Tend to exhibit co-linearity, meaning they appear along the chromosome in the order which they are expressed in the organisms

Question 21

What is apoptosis

Answer 21

Controlled cell death which shapes different body parts by the removal of unwanted cells and tissues
Cells undergoing apoptosis can also release chemical signals which stimulate mitosis + cell proliferation leading to the remodelling of tissues

Question 22

How apoptosis occurs

Answer 22

Cell shrinkage + dna fragmentation, nucleus condenses
Membrane blebbing and nucleus fragmentation
Apoptic bodies are broken off
Phagocytes engulf apoptic bodies

Question 23

How are both mitosis and apoptosis controlled

Answer 23

Hox genes

Question 24

What does it mean to be a pure breeding parents

Answer 24

Dominant dominant or recessive recessive

Homozygous

Question 25

Codominance

Answer 25

Both alleles are expressed in the phenotype when present in the genotype

Question 26

Gene locus

Answer 26

Location of gene on chromosome

Question 27

Sex linkage

Answer 27

Genes whos loci are on the same sex chromosome (x and y) have different inheritance patterns from genes on the same autosomes
X chromosome is muncher larger and has more genes present on the Y therefore they are not homologous
These genes are therefore said to be sex linked as they are affected by sex

Question 28

Null hypothesis

Answer 28

Difference between the observed value and the expected results is not statistically different, any differences are due to chance

Question 29

What is chi squared used for

Answer 29

Used to identify whether the difference between expected and observed results is statistically different

Question 30

What chromosome is haemophilia located on

Answer 30

X chromosome
X^H = dominant
X^h = recessive

Question 31

What is an autosome

Answer 31

An autosome is a chromosome that isn’t a sex chromosome
Some Autosomal genes are said to be linked and will be inherited together unless split up by crossing over
The closer the 2 genes are on the autosome the less likely they are to be split up meaning they are more likely to be inherited together

Question 32

Epistasis

Answer 32

Describes an interaction between genes are separate loci affecting a single phenotypic trait
These genes may work antagonistically or in a complimentary fashion
A gene is said to be epistatic when it’s presence modifies or surprises the effect of a gene at another locus ( the hypostatic gene)
They are sometimes referred to as modifying genes or inhibitory genes

Question 33

Recessive epistasis

Answer 33

Presence of homozygous recessive allele at the first locus prevents the expression of another allele at a second locus

Question 34

Hardy Weinberg principle

Answer 34

In a stable population with no disturbance allele frequency’s will remain constant from 1 generation to the next and there will be no evolution
P+Q=1
P^2 + 2PQ + Q^2 = 1

Question 35

Evolution definition

Answer 35

A change in inherited characteristics/ allele frequency of a group of organisms over time “ decent with modification”

Question 36

Events that might cause a change in allele frequency

Answer 36

Mutation
Genetic drift
gene flow - migration
Selection pressures

Question 37

How stabilising selection

Answer 37

Normally occurs when environment remains unchanged
Favours intermediate phenotype
Intermediate alleles will become more prevalent ( bell curve)

Question 38

Directional selection

Answer 38

• Typically associated with a change in environment
• positive selection of more extreme phenotypes
• moves bell curve to left or right

Question 39

Disruptive selection

Answer 39

• can be considered as the opposite to stabilising selection
  Extreme phenotype are selected for ( either direction ), birds beaks example
  Average phenotypes are selected against

Question 40

Genetic drift

Answer 40

Occurs in small populations, this is a change in allele frequency due to the random nature of mutation
An appearance of a new allele will have a greater impact in a small population then in a much larger population where there is a greater number of alleles present in the gene pool

Question 41

Founder effect

Answer 41

Extreme genetic drift
These small populations have much smaller gene pools that original populations + display less genetic variation
Frequency of alleles that were rare will be higher in the small population