Week 20 Flashcards
Distinguish between genes and alleles
A gene is a unit of heredity that codes for a specific protein or trait.
An allele is a version or variant of a gene. For example, “R” and “r” are two alleles of the gene determining pea shape
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Explain what it means for an allele to be dominant or recessive in complete dominance
A dominant allele determines the phenotype in a heterozygote (e.g., Rr results in a round pea because R is dominant).
A recessive allele is masked in the presence of a dominant allele and is only expressed phenotypically when homozygous (e.g., rr results in a wrinkled pea)
Explaini the relationship between Mendel’s law and meiosis
Mendel’s law of segregation states that alleles of a gene are separated into different gametes during meiosis.
This occurs because homologous chromosomes (and their alleles) segregate during anaphase I of meiosis
Describe a monohybrid cross, and explain how one can be used to determine dominance relationship between two alleles of the same gene.
A monohybrid cross examines a single gene with two alleles. For example, crossing heterozygous plants (Rr × Rr) results in a phenotypic ratio of 3:1 (dominant to recessive). The dominant allele is identified as the one that determines the phenotype in heterozygotes
Differentiate between discrete traits and continous traits
Discrete traits occur in distinct categories (e.g., round vs. wrinkled peas) and are usually determined by single genes
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Continuous traits show a range of variation (e.g., human skin color) and are influenced by multiple genes (polygenic inheritance
Differentiate between incomplete dominance, polygenic traits, and phenotypic plasticity
Incomplete dominance: The heterozygote has an intermediate phenotype (e.g., red × white flowers = pink flowers)
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Polygenic traits: Traits controlled by multiple genes (e.g., skin color)
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Phenotypic plasticity: A single genotype produces different phenotypes depending on environmental conditions
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Genotype
An organism’s genotype is the set of genes that it carries
What is mendels law of segregation
Alleles of a given gene are separated into different gametes
Differentiate between genotype and phenotype, and describe the role of the environment in phenotype.
Genotype: The genetic makeup of an individual organism.
Phenotype: The expression of traits in an organism, which depends on the genotype and can be influenced by the environment
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Role of environment: Environmental factors can impact the expression of traits (e.g., fur thickness in wolves), but not all traits are plastic. Phenotypic plasticity is determined by genotype
Define evolution
Evolution is a change in allele frequencies in a population over time.
It includes microevolution (gene frequency changes in populations) and macroevolution (branching patterns in the Tree of Life)
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List and explain the requirements for evolution by natural selection.
Variation: Individuals in a population show differences in phenotypes.
Heritability: Phenotypic differences are passed on to offspring.
Survival and reproduction: Individuals with favorable traits reproduce more successfully, increasing their fitness
Define natural selection.
Natural selection is the process where favorable traits are passed on to future generations because individuals with those traits are better suited to the environment and reproduce more successfully
Differentiate between the targets of natural selection, including genotypes vs. phenotypes, individuals vs. populations, and traits under selection vs. those not under selection.
Genotypes vs. phenotypes: Natural selection acts on phenotypes, but it changes genotypes indirectly through inheritance.
Individuals vs. populations: Selection acts on individuals, but populations evolve over time as allele frequencies change.
Traits under selection: Traits must vary, be heritable, and affect survival or reproduction to be under selection. Random events (e.g., scouts accidentally killing beetles) do not constitute natural selection
Explain two limitations and/or tradeoffs of natural selection.
Mutation is random: New beneficial traits cannot be created on demand because mutation is often detrimental and not always advantageous.
Environmental changes: The environment constantly changes, so traits that are favorable now might not be in the future. Additionally, adaptations often come with tradeoffs (e.g., energy costs of certain traits).
True or False: given a gene with dominant and recessive alleles, the dominant allele is usually the most common in a population.
false
The statement is False. Dominant alleles are not necessarily the most common in a population. The frequency of an allele in a population depends on various factors, including mutation rates, genetic drift, selection pressure, and historical population dynamics. Dominance refers to how an allele expresses itself in the presence of another allele, not its prevalence in the population.
