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Plant Genes: Exam 4 - Coggle Diagram

- - - - during meiosis, alleles segregate so that each gamete carries only 1 allele for each gene
    - - genes for different traits assort independently during gamete formation, provided they are on different chromosomes
      - in a dihybrid cross, the inheritance of one trait does not affect the inheritance of another trait
    - - in a heterozygous individual, 1 allele (dominant) can mask the expression of another allele (recessive)
      - in pea plants, the allele for tallness (T) is dominant over the allele for shortness (t)
        
        a plant with the genotype Tt will be tall
  - - - traits often result from the additive effects of multiple genes
        
        leads to continuous variation in phenotypes (i.e. skin color or height)
    - - one gene can mask or interfere with the expression of another gene
      - in digitalis, one gene affects color intensity while another gene determines pigment location
    - - a single gene can affect multiple traits
    - - genes located close together on the same chromosome tend to be inherited together
        
        results in parental phenotypes being more common than recombinant phenotypes
    - - point mutations
        
        a change in a single nucleotide that can affect the amino acid sequence during translation
      - chromosome mutations
        
        include duplications, deletions, inversions, and translocations
    - - occurs when organisms have more than 2 sets of chromosomes
        
        can arise through
        
        autopolyploidy
        
        self-fertilization
        
        allopolyploidy
        
        cross-species mating
      - can mask deleterious alleles
        
        allows for greater genetic diversity and the potential for beneficial mutations to arise
    - - traits can be influenced by multiple alleles
        
        leads to a dominance hierarchy that can vary depending on the specific alleles involved
    - - occurs when the phenotype of a heterozygote is intermediate between those of the homozygous parents
      - in snapdragons, crossing a homozygous red flower with a homozygous white flower results in all pink heterozygotes
        
        when these pink flowers are crossed, the F2 gen shows a 1:2:1 ratio of phenotypes (red, pink, white) instead of the typical 3:1 ratio seen
  - - - bet hedging
        
        increases survival chances in changing environments
      - escape from host-parasite reproduction
        
        plants can evolve new defenses against predators and parasites
      - new allele combinations
        
        increases diversity and promotes heterozygosity
    - - self-pollination
        
        pollen from the same plant fertilizes the ovule
      - benefits of sexual reproduction
        
        only achieved through cross-pollination
      - cross-pollination
        
        pollen from one plant is transferred to another plant
    - - independent assortment
        
        metaphase 2
        
        sister chromatids within the chromosome align randomly
        
        gamete combinations
        
        exponential increase in possibilities as the number of chromosomes increases
        
        metaphase 1
        
        homologous pairs arrange themselves across the equatorial plane randomly
        
        formula
        
        2^n, where n is the number of chromosomes
      - crossing over
        
        prophase 1
        
        homologous pairs come together and exchange genetic material
        
        recombinants
        
        new combinations of genes that don't resemble either parent
    - - crossing over
        
        exchange of genetic material between homologous pairs during prophase 1
      - independent assortment
        
        random arrangement of homologous pairs during metaphase 1 and sister chromatid during metaphase 2
      - homologs
        
        partner chromosomes that resemble each other in size, shape, and hereditary information
    - - homologs
        
        resemble each other in size, shape, and hereditary information
      - genetic characteristics
        
        determined by interactions of genes from homologs and other chromosomes
      - diploid individuals
        
        each chromosome has a partner called a homolog
- - - - bottleneck effect
        
        occurs when a large, genetically diverse population experiences a drastic reduction in size
        
        leads to a loss of genetic diversity
      - non-random mating
        
        leads to unequal mating opportunities
        
        results in sexual selection, where traits that enhance mating success become more common
      - genetic drift
        
        particularly impactful in small populations
      - migration (gene flow)
        
        introduces new genetic material or dilutes existing allele frequencies
      - mutation
        
        introduces new alleles
        
        can be silent and not affect phenotype but may accumulate over time
    - - natural selection occurs when certain genotypes confer advantages in survival and reproduction
        
        leads to increase frequencies of these genotypes over time
      - artificial selection is when humans selectively breed organism for desired traits
        
        impacts allele frequencies intentionally
    - - no mutation
        
        changes in nucleic acids do not occur
        
        maintains allele stability
        
        mutations can introduce new alleles but must be inherited to affect future generations
      - no migration
        
        no alleles enter or leave the population
        
        ensures genetic isolation
      - no selection
        
        all individuals have equal chances of survival and reproduction
      - large population size
        
        reduces the impact of genetic drift
        
        causes random changes in allele frequencies
      - random mating
        
        all individuals have an equal opportunity to mate
        
        prevents bias in allele frequency changes
    - - presence of multiple phenotypes within a population
        
        often results from genetic variation
  - - - stabilizing selection
        
        favors intermediate phenotypes and selects against extremes
        
        in a study of flower opening duration, flowers close sooner in dry conditions to conserve water, which stabilizes the trait over time
      - disruptive selection
        
        when both extreme phenotypes are favored over intermediate phenotypes
        
        in a cactus pop., humans tend to collect cacti with an average # of spines, leaving behind those with very few or very many spines, which increases the variation in spine # over time
      - directional selection
        
        when one extreme phenotype is favored
        
        causes population mean to shift over time
        
        in a cactus population, if peccaries prefer cacti with fewer spines, those with more spines survive and reproduce, leading to an increase in the average spine # over generations
    - - natural selection acts on existing genetic variation within a population
        
        beneficial alleles enhance survival and reproduction
        
        leads to changes in allele frequency
      - fitness is related to an organism's ability to survive and reproduce
        
        traits that confer higher fitness are more likely to be passed on to future generations
  - - - allele frequency
        
        = number of copies of an allele / total number of alleles for that gene in the population
        
        e.g. if there are 3 copies of allele w out of 6 total alleles, the frequency of W is 3/6=0.5
      - genotypic frequency
        
        = number of individuals with a specific genotype / total number of individuals in the population
        
        e.g. if there is 1 homozygous dominant individual out of 3, the frequency is 1/3=0.33
    - - gene pool
        
        the total collection of alleles in a population
        
        includes all the genetic information available for reproduction
      - population definition
        
        a population consists of individuals of the same species that occupy the same region and can interbreed
    - - allele frequencies remain constant under certain conditions
        
        no migration
        
        no natural selection
        
        no genetic drift
        
        random mating
        
        no mutations
    - - p^2 = frequency of the homozygous dominant individuals
      - 2pq = frequency of heterozygous individuals
      - q = frequency of the recessive allele
      - q^2 = frequency of homozygous recessive individuals
      - p = frequency of the dominant allele
- - - - fecundity
        
        average # of offspring produced per individual at a specific age
      - age-weighted fecundity
        
        indicates the average # of offspring per capita at a specific time
      - survivorship
        
        proportion of individuals surviving from birth to a specific age
      - age intervals
        
        often defined in specific intervals
    - - the next reproductive rate (R0) is calculated by summing the fecundity values across all age classes
      - .>1 = population growth
      - <1=population decline
    - - survivorship curves graph the relationship between age and survivorship, typically displaying 3 patterns
        
        type 2
        
        constant mortality rate regardless of age
        
        e.g. songbirds
        
        type 3
        
        high mortality in early life, but those that survive tend to live long
        
        e.g. oak trees
        
        type 1
        
        high survivorship in early and middle life, with a steep decline in old age
        
        e.g. humans
    - - essential for modeling population growth
      - provides insights into whether a population will grow or shrink based on birth and death rates
  - - - exponential growth model
        
        equation is given by dn/dt=r(n)
        
        n is the population size, r is the intrinsic growth rate, and t is time
      - logistic growth model
        
        equation is dn/dt=r(n)(1-(n/K))
        
        incorporates the carrying capacity, K, as a limiting factor
    - - the human population is currently growing exponentially, raising concerns about reaching Earth's carrying capacity
        
        as of 2022, the estimated global population is around 7.9 billion
    - - when a population exceeds its carrying capacity, it can lead to resource depletion and subsequent die-off
        
        causes fluctuations around the carrying capacity
      - carrying capacity can change over time due to environmental factors
        
        can lead to long-term impacts on population dynamics
    - - species are categorized into R-selected and K-selected based on their growth strategies
        
        R-selected species exhibit rapid growth and are often found in disturbed environments (e.g. dandelions)
        
        K-selected species grow more slowly and stabilize around the carrying capacity, often investing in defenses (e.g. avocados)
    - - exponential growth is characterized by a J-shaped curve
        
        occurs when population grows rapidly when resources are unlimited and under ideal conditions
      - logistic growth is represented by an S-shaped curve
        
        occurs when a population's growth rate decreases as it approaches its carrying capacity (K)
    - - proposed a model categorizing plants based on stress and disturbance levels
        
        how different species adapt to their environment
    - - includes aspects like growth, life history strategies, and species interactions