Inheritence and Mandelian Genetics - Genetics 1 & 2 Flashcards
Genetic Diversity
Variation in genetic traits within a population.
Why is genetic diversity essential for evolution?
In order for traits to be selected for, genetic diversity is needed (different combinations of alleles).
Mutation
Change in bases of DNA sequence affecting genetic information - including functional and non-functional genes.
Karyotypic Changes
Alterations in chromosome structure or number.
Evolution
Process by which species adapt over time.
DNA Replication
Process of copying DNA before cell division.
Polymerases
Enzymes that synthesize DNA strands.
How is erorr rate reduced in the DNA sequence during replication
Proofreading and mismatch repair
Proofreading
Error-checking mechanism during DNA synthesis in proofreading domains of polymerases
Mismatch Repair
Correction of base-pairing errors in DNA.
Base-Excision Repair
Repair mechanism for oxidative DNA damage.
How else can mutations occur apart from random changes to neucleotides?
DNA Damage. Agents causing mutatations (mutagens) cause their accumulation
Why do we use harmful chemicals
They havn’t been discovered yet as a mutagen/carcinogen
Deleterious
Negative, causing harm
Why do organisms have fine-tined mutation rates
- Too many mutations would be deleterious
- Mutations generate genetic diversity on which evolution acts
Successful organisms have evolved to repair their DNA efficiently, leaving just enough genetic variability for evolution to continue.
Transition Mutation
E.g. C - T
Substitution of one purine for another purine.
Transversion Mutation
E.g T - G
Substitution of a purine for a pyrimidine.
3 types of substitution mutations
- Silent
- Nonsense
- Missence
Missense Mutation
Single base change alters amino acid in protein.
Silent mutation
No effect because of the degenerate nature of amino acids
Why are missence mutations sometimes managable
R groups of the different amino acid being coded for can have the same charge/polarity (properties) so the 3D structure it folds to is similar enough to carry out its function.
Frameshift Mutation
Insertion or deletion alters reading frame of DNA. Every subsequent codon is changed and is are each/most amino acids coded for in the final protein. Protein is unable to bind so unexpressed
Nonsense Mutation
Mutation that creates a premature stop codo, producing a truncated protein.
Where are frameshift mutations common?
In tumor supressor genes
Sequence Divergence
Variation in DNA sequences among species. Used as a measure of evolutionary relatedness.
How is sequence divergence used to measure evolutionary relatedness?
Sequences of different organisms are compared for differences, less differences = more closely related
Conservation of sequences between different species
These sequences have vital fucntions for life. For instance the genes coding for histones which bind to DNA that wraps around, giving histones their shape.
Conserved Sequences
DNA sequences that remain unchanged across species.
Genome Instability
Allows frequent mutations leading to genetic diversity that natural selection can act on. It is also a hallmark of cancer
Karyotype
Visual representation of a person’s chromosomes - can be used to identify oddities in chromosome number/structure.
Structural variants of karyotype variation
IMAGE
Cancer Karyotypes
Extreme of genetic diersity - chromosomal variations associated with cancer.
Source of genetic diversity that isn’t mutation
Chromosomal changes during viral infection and meiosis
HIV Resistance
Genetic mutation providing immunity to HIV.
Natural Selection
Process where organisms better adapted survive.
SARS-Cov-2 Mutation
Genetic changes affecting virus infectivity.
Mendel’s pea experiments
Only used true breeding plants and studies 7 of the plant’s phenotypes. E.g pea shape and colour, and flower colour and position.
What do we assume when doing genetic crossing experiments?
Gnetic occurances have direct impact on phenotype - this only occurs when 1 gene impacts a specific phenotype
True breeding
Phenotypes of offspring are the same as in the parents regardless of how many times they are crossed - nothing new.
What did Mendel deduce?
- Traits are controlles by a pair of inherited “factors”
- One is dominant and one is recessive
- Pairs segregate randomly during gamete formation - causing different impacts on the phenotyoe
Dominant and recessive alleles are contrary to the priginal blending model of genetic inheritence
Previously thought that phenotypes olccured due tp blending of parents characteristics (gene)
Predict the outcomes of an RR x rr and Rr x rr cross
- RR x rr: 100% Rr
- R r X rr: 50% rr, 50% Rr
Knockout mice
Genetically modified lab mice with one or more genes that have been intentionally inactivated
You breed 2 heterozygous knockout mice and need homozygous knockout offspring (25%). You notice the litter is smaller than normal and when you run a gel electrophoresis you notice none of the pups are homozygous for the knockout gene. Why?
Pups with homozygous knockout are not viable for life so don’t go to full term, hence the smaller litter. Essential genes encoding proteins vital to cellular life were knocked out.
Embryonic lethality
The death of all organisms in a population during the embryonic period. It is a common phenotype in mice that have genetically engineered mutations.
What did Mendel seek to investigate with his usage of dihybrid crosses?
Are characteristics of the peas (heritable traits) inherited independently (in an identifiable way from each other) or are they linked.
Dihybrid crosses
Used to investigate the inheritence of two different traits and how they are combined in the offspring.
Mendel’s law of inheritence
- Law of dominance
- Law of segregation
- Law of independent segregation
Law of segregation
When a gamete is formed, the two alleles at a specific location separate, and each gamete has an equal chance of containing either allele.
Law of independent segregation
During reproduction, two genes independently segregate, each independently determining one aspect of the phenotype
Law of dominance
When a pair of contrasting characters are present together, only one expresses itself, while the other remains suppressed. (dominance vs recessiveness).
Pleiotropy
Single gene mutation can cause a range of phenotypes
So, the pheotypes don’t appear the same in 2 patients
Gnetic heterogeneity
Same penotype can be cause by a range of different genes. As a result, certain symptoms can be difficult to diagnose.
Polygenic
Traits controlled by more than one gene
Examples of polygenic traits
Human height, eye, hair and skin colour.
These all have lots of variation within a popualtion.
Codominance
Two alleles are expressed equally in an organism, resulting in the appearance of both traits/phenotypes.
Incomplete dominance
Two alleles are blended/mixed rather than both expressed. It’s also known as partial dominance, semi-dominance, or intermediate inheritance.
A white and red flower would prodice a pink flower.
