Ch 14 A
What is crossing over, what is its purpose, and when does it occur?
During Prophase I, DNA segments between homologous chromosomes are exchanged in order to ensure genetically unique daughter cells
What are the two kinds of dominance and how do they differ?
Incomplete dominance - mix of the two traits (pink)
Codominance - some of both traits show (splotches)
What is the basic structure found in all viruses
Genome and protein capsid; envelope sometimes
What are the two broad sources of genetic variation?
Mutations and recombination
What defines a species according to the BSC?
Reproductively isolated
What is the phenotypic ratio of a dihybrid cross under independent assortment?
Two heterozygous traits in two organisms cross to form 9:3:3:1
What is the purpose of a testcrossing?
To determining the genotype of a parent with dominant phenotype (AA or Aa)
How does the lysogenic cycle of virus reproduction work(simply)?
viruses integrate into a host cell's genome and replicate silently
What is the difference between positive and negative selection?
Positive increases beneficial alleles; negative removes harmful alleles.
What are the limitations of the Biological Species Concept?
Asexual organisms – Cannot apply
Fossils/extinct species – Cannot test
Hybridization complications
How many human chromosomes are present at each stage of meiosis? (Hint: Consider the difference between a chromosome and chromatid)(start, before I, after I, after II)
46, 46, 23, 23 vs 46, 92, 46, 23
Do incomplete dominance and codominance violate Mendel’s law of segregation? Why or why not?
No because dominance is a difference is in phenotype expression, not allele transmission
What are the two methods of virus reproduction and what determines which it will utilize?
What is the difference between a species and a population?
A species is a group of individuals that can exchange genetic material through interbreeding or share alleles through reproduction while a population is group of a species living in the same geographic location
How can species who live in the same area still not experience gene flow?
Behavioral isolation - differences in courtship signals or behaviors prevent individuals from recognizing each other as mates.
What is the difference between Mendel's two principles?
Segregation is the separation of alleles for a single gene during gamete formation, while independent assortment is the random assortment of alleles for different genes during gamete formation. (receiving recessive vs dominant vs each trait separates alone)
What are the two kinds of nondisjunction and which is more harmful?
First and Second Division Nondisjunction, in first division every gamete will have an incorrect number of chromosomes
Why are viruses so successful when they cant even reproduce on their own?
Their ability to use host cell machinery to replicate, their rapid release of large numbers of new viral particles, their high mutation and recombination rates that help them evade immune defenses, their potential to switch hosts, their capacity to integrate into host DNA in the lysogenic cycle, their structural and receptor specificity that enables efficient infection, their effective population-level spread, and their ecological impact, such as lysing huge numbers of microbial cells each day.
What is the frequency of a? 30% aa 40% Aa 30% AA
%50
Why is reproductive isolation considered essential for defining species under the Biological Species Concept?
Without reproductive isolation, gene flow continues, preventing populations from becoming genetically distinct species.
How are Mendel’s laws physically explained by meiotic processes?
Segregation happens because of the separation of homologous chromosomes in meiosis I, independent assortment from the random alignment of different homologous pairs at metaphase I
How can two parents can produce offspring with allele combinations neither parent visibly shows?
Crossing over creates new combinations of alleles on each chromosome, producing recombinant gametes. These gametes can carry allele pairings not present in either parent’s phenotype, leading to offspring with new trait combinations.
How do antigenic drift and antigenic shift differently influence the influenza virus’s ability to overcome existing immunity in a population?
Antigenic drift introduces gradual mutations that slightly change viral proteins, weakening immune recognition over time, while antigenic shift results from recombination between different flu viruses, producing major new protein variants that can escape widespread immunity all at once.
What are the 3 methods to measure genotype/allele frequency and what are their strengths/weaknesses?
Observable traits are easy to measure but fail when traits are influenced by multiple genes, the environment, or when heterozygotes cannot be distinguished. Gel electrophoresis can detect protein differences caused by different alleles but cannot detect silent DNA mutations. DNA sequencing is the most accurate because it identifies all nucleotide differences, but it requires collecting and analyzing genetic samples.
What are the two kinds of allopatric speciation and how do they differ?
Dispersal: Individuals colonize a new area.
Vicariance: Where a geographic barrier arises, a population splits into two separate populations