✅ M1 - Genetics & Mutations - Human Genome project Flashcards
first 9 cards from L1, the rest from L2
1
Q
What is the difference between genotype and phenotype?
A
- Genotype
- Genetic make up of an individual
- Combination of alleles an individual possesses for one or more genes. - Phenotype:
- Individual’s observable inherited characteristics.
- Appearance, physiology, or behaviour.
- A trait is controlled by proteins (produced by alleles), and sometimes the environment.
- The environment can influence an individual’s physiology (e.g. lifestyle, nutritions) by switching gene ON/OFF -> bigger scale influence natural selection.
2
Q
Basic features/structure of DNA? Function of DNA?
A
- Features:
- Double helix with 2 strands
- Held together by hydrogen bonds between pairs of bases: A-T and C-G - Reproduction: Cell makes a duplicate copy of each DNA strand during cell division
- Cell division (mitosis): replication of genetic material passed on from mother → daughter cell
+ involves semi-conservative replications (one strand from old cell in each new cell)
+ during prophase, DNA condenses into chromosomes
- Gamete cell production (meiosis): in each gamete, only one chromosome from each pair is present - Protein synthesis:
- Transcription: DNA undergoes this process to form RNA (single-strand) where Uracil (U) base is used instead of Thymine (T)
- Translation: RNA obtained from transcription is used to get code for specific proteins
=> Allow expression of genes
3
Q
What is polymorphism of gene?
A
- Polymorphism: different alleles for a gene locus
- Usually arise from mutations
- Responsible for hereditary variation.
- Two alleles per locus
- These alleles can be same (homozygous) or different (heterozygous) - Relationships:
- Dominant: expressed (1) - allele codes for functioning protein
- Recessive: expressed if homozygous - allele codes for non-functioning protein
- Co-dominant: both expressed
=> These relationships reflect the relative characteristics/abundance of the proteins.
4
Q
What are chromosomes?
A
- Condensed genetic material
- Each human has 23 pairs of chromosomes -> 46 DNA
- 22 pairs of autosome (physical features)
- 1 pair of sex chromosomes (either X-X or X-Y)
=> All chromosomes during are shown in the karyotype
5
Q
How is allele related to natural selection?
A
- Allele frequency: whether an allele is rare or common in a population, is linked to the genetic fitness of the organism.
- Genetic fitness -> reproductive success: survival to reproductive age + mating success + healthy progeny.
- If an allele is advantageous, it is likely to be passed on and persist in the population.
- If the environment changes, the frequency may change again.
6
Q
What are 3 examples of mutations/alleles that assist in natural selection?
A
- Mutations that allow us to diversify our diet
- A mutation that maintains production of lactase during adulthood -> allow ancestors to farm cattle
- A mutation that reduce functions of bitter receptor allowed us to eat bitter vegetables (e.g. broccoli…). - Mutations that allow us to combat diseases
- Sickle cell anaemia: carriers are asymptomatic and get protection from malaria.
- Mutation on immunity: People homozygous for a mutation affecting immune cells’ receptors (CCR5) are asymptomatic and immune to HIV.
=> BUT! Mutated immune cells are less effective against pathogens common in developing countries. - Temperature sensitive alleles
- Tyrosinase = enzyme which controls the production of melanin (dark pigment for hair/skin)
- Example: Siamese cats only have melanin in their cool extremities -> allele with high-temp unstable tyrosinase
7
Q
What is meant by multifactorial traits?
A
- The component/distribution of genes and the environment that contribute to an individual’s continuum phenotype (e.g. skin colour, height, weight, behaviour)
- Evidence: twin studies
- Identical twins share greater similarity for a particular trait than fraternal twins -> genetic factor
- Less than 100% similarity in identical twins indicates that DNA alone does not determine disease occurring -> environmental factors
8
Q
What is meant by mutation?
A
- Mutation = permanent alteration in the DNA sequence passed on into daughter cells and sometimes into gametes.
- Mutations vary in sizes/severity:
1. Micro: SNP within a gene
2. Macro: affecting one or multiple chromosomes
9
Q
What are the types of mutation?
A
- Hereditary (germ line) mutation: inherited from a parent gamete to offspring.
- Acquired (or somatic) mutation = occurs at some time during a person’s life and present only in certain cells.
-> random mutation
-> if present in gamete, can be passed to offsprings
10
Q
What are the causes of new mutation?
A
- Environment:
- Mutagens (e.g. radiations) causing breaks in DNA base pairs.
- Biological factors (e.g. viruses) causing harm to important DNA region. - Intrinsic:
- Errors during DNA replication before mitosis (~2000 errors, but have good repair mechanism)
- Errors during DNA repair (prone to more errors due to ageing)
- Errors during meiosis (e.g. Trisomy 21)
11
Q
What are 2 types of macro mutations (affecting chromosome)?
*Aberration = deviates from the norm
A
- Numerical aberrations:
- Error in distributing single chromosome (in meiosis), resulting to either 47 or 45 chromosomes in human cells
- Example: Trisomy 21 (Down Syndrome) - Structural aberrations:
- Errors in a single chromosome, 3 types: deletion, duplication, inversion.
- Errors between two or more chromosomes:
+ Insertion: one part of a chromosome is transferred to a different chromosome
+ Translocation: switch gene between chromosome (could also be the cause for trisomy 21 Down syndrome)
12
Q
What are the 3 types of error in a single chromosome (structural aberrations of macro mutations) & how they affect the genetic material?
A
- Deletion: missing a part of gene/allele → limit variation and under-expression of gene
- Duplication: over-expression of genes → dominant
- Inversion: reverse order of a gene → effect depends on the gene types
13
Q
What are types of micro mutations in DNA (SNP)?
A
Single nucleotide polymorphism (SNP) can produce silent, nonsense (STOP), or missense (wrong protein) mutations.
HOW?
1. Insertions and deletions of base nucleotides -> frameshift mutations
2. Frameshift mutations: usually lead to an early STOP codon, usually very bad: shorter protein or no protein.
3. Insertion of 3 bases: only adds one codon (no frameshift).
14
Q
Why/How does a location of mutation in DNA matters? (more examples maybe)
A
- Regulatory Regions: Mutations occurring in non-coding regions of DNA, such as enhance elements (EE) that control gene expression.
-> Example: SNP (from C -> T) mutation in enhance region of lactase production) - Disease Risk: Some mutations are associated with an increased risk of certain diseases.
-> Example: repeating 3-base-insertion of CAG creating genetic stutter
=> HOW? Preventing other genes to work properly (e.g. Huntington Disease)
15
Q
What are the 3 findings we have learnt from the Human Genome Project (HGP)?
A
- Humans only have ~20,500 genes, increasing complexity of organisms doesn’t necessarily mean longer genes
-> only 2% of human DNA codes for genes, the rest are non-coding
-> 50% are from viruses - Humans are 99.9% identical, only 0.1% variation due to SNP which most occurs in outside genes (e.g. non-coding regions of DNA)
- Location of 1,400 disease-causing mutations identified -> before, only know <100
