Genetic Basis of Evolution Flashcards
Gregor Mendel (1822-1884)
Considered to be the father of genetics
Conducted groundbreaking work on theories of heredity
The understanding of heredity is vital for the understanding of evolution
Heredity
The transmission of “traits” from parents to offspring
Genes
any portion of chromosomal material that potentially last for enough generations to serve as a unit of natural selection
Particular units of inheritance that are passed from parents to offspring
Locus / Loci
a place on a chromosome where genes affecting a particular trait occur
Homozygous
when the mother and father contribute identical genes for the locus in question
Heterozygous
When the mother and father contribute different genes for the locus in question
Genotype
the genetic code carried by a particular individual- metaphor- a recipe. You have the genotype and the environment which creates phenotype
Phenotype
the expression of a particular genotype
The result of the interaction between the environment and the genotype
Dominant gene
a gene that is expressed in the phenotype regardless of whether it is homozygous or heterozygous
Recessive gene
a gene that is expressed in the phenotype only when it is homozygous
Eye color is classic example
Genes / Heredity
Genes are particular
Particles retain their integrity and are not diluted or reduced when combined with the particles of the mate
Discrete trait
a trait with a small number of clearly separate phenotypes (e.g. eye color)
Continuous trait
a trait with a large number of alternative phenotypes (e.g. height)
Normal Adult Genes
Each normal adult carries a pair of genes for each trait
One gene comes from the mother, one gene comes from the father
When these genes are identical, they are homozygous
When these genes are different, they are heterozygous
Diploid
the condition of having two sets of chromosomes. Normal body cells are diploid
Haploid
the condition of having one set of chromosomes. Sex cells (eggs and sperm) are haploid
Genes / Particles
Although pairs of genes do not dilute or change each other permanently, they can influence each others expression
Some genes can overshadow the effects of other genes (dominance effects)
The dominant gene is expressed in the heterozygous and homozygous conditions
The recessive gene is only expressed in the homozygous condition
The effects on one gene have an effect on another.
Deoxyribonucleic acid (DNA)
the molecule that contains the information needed to build cells and control inheritance
Chromosome
structures in the nucleus cell that house DNA. Chromosomes contain DNA and proteins bind to it
Can be thought of as “a long string of genes”
Alleles
variant forms of a single gene. Alternatives at a particular locus
Two thirds of all loci have only a single allele
Mutation
a heritable change in the base sequence of the DNA genome
A mistake in gene copying
The ultimate source of all new alleles. How novelty enters the equation
Occurs when sex cells are coming together.
DNA: A Chemical Code for Proteins
DNA contains 2 strands of complimentary pairs
Adenine (A) always pairs with Thymine (T)
Guanine (G) pairs with Cytosine (C)
These are called base pairs
This allows DNA to separate and replicate, forming exact copies
Codon
a set of three nucleotides (base pairs) along the DNA sequence that specify one amino acid
Alleles may be selectively neutral
(Reasons for Genetic Variation)
Alternative alleles at a particular locus may produce equally fit phenotypes
Blood types??? Remains a topic of debate
Environmental Variation
(Reasons for Genetic Variation)
Changing or fluctuating environments may select different alleles
Heterozygote superiority
(Reasons for Genetic Variation)
In some cases, heterozygotes are fitter than homozygotes
i.e. sickle cell anemia
Frequency-dependent selection (Reasons for Genetic Variation)
When natural selection favors an allele when it is rare, but disfavors it when it becomes more common
Mutation (Reasons for Genetic Variation)
Gene copying errors; the ultimate source of all genetic variation
Most mutations decrease fitness and are quickly eliminated from the population
Rarely, but often enough, mutations increase fitness and are spread throughout the population
Random gene copying errors
Natural selection cannot choose which mutations to make
Selection evaluates these alternatives once they exist, eliminating the harmful ones and spreading the beneficial ones
Common Mistakes in Evolutionary Thinking
“Evolution has a goal”
Natural selection is a description of a process that lacks consciousness, intentions, morals, and goals
Why tigers have stripes
Not because evolution wanted them to blend in against a forested background
Because at some point in their past, striped tigers out-reproduced other tigers
Common Mistakes in Evolutionary Thinking
“Evolution works for the good of the species”
DNA can develop any type of mechanism that assists in its own replication, even when the mechanisms involve inhibiting other conspecifics from reproducing
Copulatory plugs in some insects and reptiles
After a male mates with a female, he secretes a thick “glue” preventing other males from having successful intercourse with the female
This clearly works against the good of the species
Common Mistakes in Evolutionary Thinking
“Evolution and optimization”
Evolution does not find the global optimum. Instead, it finds solutions, some of which may be local maxima
Herons, pelicans, osprey, and loons all catch fish for a living, but they do so in different ways.
There is more than one way to get your genes into the next generation
Each species provides a different example
