Biomolecules - Chromsomal Inheritance And Evolution Flashcards
Proving DNA as genetic material
- Miescher: isolated and identified nucleic acid
- Wilhelm Roux: when the cell divides, organelles aren’t distributed equally, but the nuclear material is. He decided that the nuclear material must be the genetic material
*Hershey-Chase proved that its nucleic acid and not protein that is genetic material
- sulphur 35 is found in proteins but not DNA. Because the protein coat remained outside the cell, it could not be the genetic material
- phosphate 32 is found in DNA but not in protein. Because the radioactively labelled DNA were in the cell, it proved that DNA is the genetic material
Sex-linked traits
*We have two chromosomes that act as the sex determining chromosomes. The father determines the gender of the offspring since the mother only has the X chromosome to give.
*there are some other genes on these chromosomes. For example, the mutation that cause red green colourblindness and haemophilia are recessive mutations found on the X chromosome.
Genetic recombination and gene mapping
*we count chromosomes by the number of centromeres.
- During prophase I of meiosis, homologous chromosomes pair up and form a tetrad in a process called synapsis
- at a certain point (chiasma) they might cross over forming a synaptonemal complex through which some DNA swaps places. This is called genetic recombination. This can also occur between sister chromatids, but because they’re identical, it makes no difference
- you can use genetic recombination to find the locations of genes on a chromosome called gene mapping
- Genes farther from each other on a chromosomes are more likely to cross over because there’s more space for it to occur. Centimorgan (m.v) is the distance between genes for which one product of meiosis in 100 is recombinant.
Extranuclear inheritance
*mitochondria and chloroplasts have their own DNA and can replicate their DNA and themselves independently. Endosymbiotic theory suggests they were once independent prokaryotes that were engulfed by larger ancestral eukaryotic cells.
* mitochondria: mtDNA has about 37 genes which are mostly related to cellular respiration
*chloroplasts: has granum made of thylakoids where photosynthesis takes place. cpDNA has about 100 genes which are mostly related to photosynthesis
*the zygote gets its mitochondria directly from the eggs when the zygote replicates itself, it also replicates those mitochondria. Both mitochondria and chloroplasts show maternal inheritance (contrary to Mendelian genetics which focuses on half from egg and half from sperm) - work by Carl Correns
Penetrance and Expressivity
-Constant expressivity: uniform or constant expression of a gene in individuals with the specific genotype
-Variable expressivity: a single genotype produces a range of phenotypes that differ in degree or magnitude of expression of the particular trait
-Penetrance: percentage of people with a specific genotype who express the phenotype associated with the underlying genotype
Fecundity
How easily and how often an organism reproduces offspring.
High fecundity is selected for
Alternative selection
*Group selection: genetic traits that benefit the group as a whole will be selected for even if they don’t increase the fitness of the individual
- survival after reproduction
*Artificial selection: an outside individual selects for which organisms have a desirable trait
Genetic drift, bottleneck effect and founder effect
*Genetic drift is about random changes in the reproduction of populations. It’s much more likely with smaller populations and is a mechanism of evolution
Types of genetic drift
- bottle neck effect: a major disaster or event kills off most of the population
- founder effect: part of the population migrate to a new region forming a new population there and many alleles disappear from the original group
Inbreeding
-Larger gene pools allows for more genetic diversity which allows a group to be able to adapt to its environment.
-Inbreeding is when people in a population selectively reproduce with a specific smaller group within the larger population. When it’s non human, it’s often because of geographical barriers.
-Inbred populations can have a lot more people that are carriers for diseases. But this is more of a concern for autosomal recessive conditions.
Reproductive isolation
Prezygotic: forces preventing organisms from producing offspring before a zygote is formed.
- temporal/habitat isolation
- behavioural isolation
- mechanical isolation (physical inability)
- gametic isolation (fertilisation isn’t possible)
Postzygotic
- zygote mortality
- hybrid in viability
- hybrid sterility
If two organisms are separated by any of these barriers, they’re not in the same species.
Disruptive selection
Two extremes on a continuum are selected for
