Genetics and Evolution Flashcards
Homologues
The two copies of each chromosome
What is unqiue about the male sex chromosomes?
They are not a homologous pair. (because one is an x-chromosome and one is a y-chromosome)
An allele in which only one copy is needed to express a given phenotype.
dominant allele
An allele in which two copies are needed to express a given phenotype.
recessive
Homozygous vs. Heterozygous vs. Hemizygous
- Homo
- If both alleles are the same for a given gene
- Hetero
- If the alleles are different for a given gene
- Hemi
- When only one allele is present for a given gene (i.e. male y-chromosome)
One dominant allele and one recessive allele
Complete Dominance
More than one dominant allele
Codominance
No dominant alleles. Heterozygotes have an intermediate phenotype.
Incomplete Dominance
The extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it,
(measured by the proportion of carriers showing the characteristic phenotype.)
Penetrance
Full vs. High vs. Reduced vs. Non Penetrance
- Full Penetrance: 100% with allele show symptoms
- High: Most but not all with allele show symptoms
- Reduced/Low: Some with allele show symptoms, some don’t
- Non-penetrance: a person carrying the allele does not express symptoms
Different manifestations of the same genotype across a populations.
Expressivity
(constant vs. variable)
- Constant: All people with specific genotype express the gene the same
- Variable: People have same genotype, but have many phenotypes
Mendel’s First Law of Segregation
Allele pairs segregate during gamete formation, and randomly unite at fertilization.
List the four basic tenants of of Mendel’s First Law.
- Genes exist in alternative forms
- Each gene has 2 alleles (one inherited from each parent)
- Alleles segregate during meiosis, resulting in gametes that carry only one allele for a given gene
- If two alleles are different, one is is expressed and the other is silent (recessive vs. dominant)
Mende’s Second Law (Law of Independant Assortment)
Alleles of one gene sort into gametes independently of the alleles of another gene.
(Inheritance of one gene does not affect the inheritance of a second gene)
Advantageous vs. Deletarious Mutations
- Advantageous: Positive result from mutations
- Deletarious: Detrimental results from a mutation.
Flow of genes between species through hybrid offspring.
Leakage
Genetic Drift
Change in allele frequencies within a population (overtime) due to chance events.
List and explain two types of genetic drift.
- Bottleneck
- Severe decrease in population size, causing reproductive isolation
- Could be the result of natural barriers or catostrophic events
- Results in a significant decrease in one allele and increase in the other allele.
- May result in in-breeding with small population size
- Founder Affect
- When a new population is formed/founded in a new location
- Allele frequencies can change (from reproductive isolation), resulting in a genetic pool differant than the parent population
- May result in in-breeding with small population size
Ultmately results in a reduction of genetic diversity and increase in certain traits/diseases within a population
In-breeding is the mating of two genetically related indifivuals. Thus, what does inbreeding promote, in relation to alleles.
Promotes homozygosity (homozygous dominant and recessive genotypes)
What are inborn errors of metabolism and why is it important to identify that early in a persons life?
- Defects in genes required for metabolism
- If not diagnosed in a timely manner, can lead to permanent damage from build up of metabolites.
Loss of genetic variation causing reduced fitness within a population.
In-Breeding Depression
Induction of unrelated individuals to a breeding group. Introduces genetic diversity and increases fitness within a population.
Outbreeding/Oucrossing
Diagrams that predict the relative genotypic and phenotypic frequencies resulting from the crossing of 2 individuals.
Punnett Squares
A _________ is a cross in which only one trait is being studied.
Monohybrid
Explain Mendel’s Monohybrid Cross with Pea plants (including results for F1 and F2 generation)
- Crossing of Homozygous P Generation (w/ PP and pp)
- 100% Pp (heterozygotes) where only dominant allele was expressed
- Crossing of Heterozygotes of F1 Generation
- 1:2:1 genotypic ratio
- 3:1 Phenotypic ratio
Crossing of heterozygotes with __________ results in a 1:2:1 genotypic ratio and 3:1 phenotypic ratio.
Complete Dominance
Used to determine and unknown genotype.
Test Cross
How is a test cross used to determine an unknown genotype. What are the results?
- Unknown genotype is crossed with homozygous recessive alleles
- If unknown genotype is heterozygote
- Genotype is 50:50 (1:1 ratio)
- 50% Heterozygous (dominant phenotype)
- 50% Homozygous Recessive
- Genotype is 50:50 (1:1 ratio)
- If unknown is homozygous
- 100% heterozygotes for a trait with complete dominance
This type of punnett square results accounts for the inheritance of 2 different genes.
Dihybrid Punnet Square
Genes on different chromosomes that segregate independantly into gametes
Unlinked Genes
Linked genes thay are on the same chromosome and are often inherited together (due to close proximity).
Linked Genes
What does a dihybrid cross for 2 heterozygotes with complete dominance result in in?
9:3:3:1 Ratio (3:1 phenotypic ratio holds for each trait)
Sex linked diseases are ____-linked.
X-Linked
(This is due to the fact that men only get one X chromosome, which they inheret from their mother. Even if the trait is recessive, the male will still express the gene due to that fact they are hemizygous for that gene. In contrast, women get two XX chromosone, thus, if they inheret a recessive chromosone for a specific gene, they will only show it if the are homozygous for that gene. If they are heterozygous, the dominant gene will only be fully expressed)
Unless otherwise stated on MCAT, always assume that sex-linked traits or x-linked and ________ _________.
Recessive
Likelihood of two alleles being separated during crossing over in meiosis.
Recombination Frequency
(Greater recombination frequency is often directy proprotional to the distance between these genes on the chromosome. Two alleles with a smaller distance between them will have a lower recombination frequency and will be less likely to separate during meiosis)
_________ _________ can be made using the recombination frequency and use centimorgans as a scale.
Genetic Map
- Measures the distance between two genes on a chromosome.
- Measured using centimorgans (represent the percentage to which recombination will occur between to two alleles
- i.e.: 15 centimorgan units = 15% change of recombination
Asserts tthat if the population meets specified criteria, the allele frequencies will remain constant.
Hardi-Weinberg Equilibrium
What are the criteria for Hardi-Weinberg Equilibrium?
- A large breeding population.
- Random mating.
- No mutation (or significant changes in allelic frequencies)
- No immigration or emigration.
- No natural selection.
What are the two Hardy-Weinberg Equilibrium Equations? What do each of them tell?
- p + q = 1
- Tells each allelic frequency
- p2 + 2pq + q2 = 1
- Tells about genotypes and phenotypes
What can the Hardy-Weinberg equations tell, in addition to the allelic/genotypic/phenotypic frequencies of the current population?
Can be used to demonstrate that evolution is NOT occuring by showing that allele frequencies of following generation are unchanged from parent generation
Variations within a population that increase an individual’s fitness (for the environement), will have a greater opportunity of reproductive success.
Natural Selection
What is differential Reproduction?
The idea that those organisms best adapted to a given environment will be most likely to survive to reproductive age and have offspring of their own. (Neo-darwinism)
Theory that the genetic success of individual organisms is often dependent upon the cooperative success of the group.
Inclusive Fitness
Evolution to be a slow process with intermittent rapid bursts of evolutionary activity
Punctuated equilibria
Naturally occuring differences in form between members of the same population (species)
Polymorphism
Rapid emergence of species from a common ancestor, each of which occupies it own niche. (not punctuated equilibrium)
Adaptive radiation
Evolution in which dissimilar species gradually become more similiar.
Convergent
Type of evolution in which closely related species gradually become very different.
Divergent Evolution
When a population splits in two, yet they continue to evolve similarly.
Parallel Evolution
