Cellular and Genetic Mechanisms of Development and Evolution
Mitosis, Meiosis, and Development
Mitosis is crucial for cell proliferation during development post-fertilization.
Meiosis is important before development, as it produces gametes with genetic variation.
Genetic variation from meiosis is essential for natural selection, as it provides a diverse pool of traits that can be selected for or against in a changing environment.
Cell-Cell Recognition in Sea Urchins
Role in Polyspermy: Prevents multiple sperm from fertilizing one egg, ensuring correct chromosome number.
Blocking polyspermy is vital for maintaining stable chromosome numbers and normal cell division.
Gamete recognition relates to RIMs by ensuring species-specific fertilization, thus preventing the formation of hybrids with potentially unviable genetic combinations.
Mendel’s and Darwin’s Work
Mendel’s work on genetics provided the mechanism for heredity that Darwin’s theory of evolution lacked.
Darwin’s concerns: Lack of a mechanism to explain how traits were passed down.
Mendel’s particulate theory of inheritance showed that traits are inherited as discrete units (genes), which could undergo natural selection.
Allelic Interactions
Single Locus: Incomplete dominance or codominance.
Multiple Loci: Epistasis, where the expression of one gene affects the expression of another.
These interactions can both align with and violate Mendel’s assumptions (independent assortment, dominance).
Important for maintaining genetic variation and affecting allele frequencies.
Developmental Plasticity
Developmental plasticity allows an organism’s phenotype to change in response to environmental conditions.
This flexibility shows that the genotype-phenotype relationship is not always direct and fixed.
Plasticity relates to fitness and natural selection as it enables organisms to adapt to varying environments, supporting Darwin’s ideas on evolution through embryonic similarities among species.
Mapping Sexual Life Cycle Processes
Mitosis occurs in the diploid phase, meiosis occurs before gamete formation, and fertilization restores diploidy.
Hybrid sterility often results from disrupted meiosis due to chromosomal incompatibilities.
Restoration on a chromosomal level might involve changes that align chromosomes properly during meiosis.
Population Definitions
Population Genetics: A group of individuals of the same species, living in an area, sharing a common gene pool.
Population Ecology: Focuses more on the number of individuals, their distribution, and their interactions with the environment.
The definitions differ due to the focus of each field: genetic composition vs. ecological dynamics.
Problems for Small Populations
Genetic Issues: Reduced genetic diversity, inbreeding, genetic drift.
Evolutionary Issues: Less raw material for natural selection, reduced ability to adapt.
Ecological Issues: Increased susceptibility to environmental changes, reduced resilience.
These factors can lead to reduced fitness and an increased risk of extinction.
Unit 1: Diverse Cells from a Single Zygote
Start with a zygote, a single cell formed by the fusion of sperm and egg.
Include stages of embryonic development: cleavage, gastrulation, organogenesis.
Show how differential gene expression leads to cell differentiation.
Illustrate the role of signaling pathways and environmental factors in cell specialization.
Add the concept of stem cells and their potential to become various cell types.
Unit 2: Genetic and Phenotypic Diversity in Offspring
Begin with a pair of individuals, highlighting their genotype and phenotype.
Show how meiosis creates genetic variation in gametes (crossing over, independent assortment).
Include fertilization, resulting in a genetically unique zygote.
Depict Mendelian genetics (dominance, segregation, independent assortment).
Add non-Mendelian genetics (incomplete dominance, codominance, polygenic traits).
Illustrate environmental influence on phenotype.
Unit 3: Population Divergence and Speciation
Start with a single population.
Show genetic variation within the population (mutations, sexual reproduction).
Add mechanisms of evolution (natural selection, genetic drift, gene flow).
Include geographic and reproductive isolation leading to speciation.
Illustrate allopatric and sympatric speciation.
Add adaptive radiation as a concept.
Unit 4: Environmental Support for Diversity
Begin with different ecosystems and their characteristics.
Show how energy flow (food chains/webs) and nutrient cycling support diverse life.
Include various biomes and their specific climates and species.
Illustrate interactions between species (predation, competition, mutualism).
Add human impacts and conservation efforts for maintaining biodiversity.
Rare Salamander Reproduction:
Correct Answer: b. Sperm trigger egg activation.
Explanation: In some species, sperm are necessary to activate the egg to start development, but they do not contribute genetically in these specific cases.
Genetic Variation According to Mendel’s Model:
Correct Answer: d. Genetic hitchhiking (genes on the same chromosome tend to be inherited together)
Explanation: Mendel’s model discusses diploidy, heterozygosity, and independent assortment as means of maintaining genetic variation. Genetic hitchhiking is not a part of Mendel’s model; it refers to the process where genes linked to a beneficial allele also get passed on.
Genetic Variation:
Correct Answer: c. must be present in a population before natural selection can act upon the population
Explanation: Genetic variation is a prerequisite for natural selection. It is not created by natural selection nor does it arise as a direct response to environmental changes.
Risks for Small Populations of Gopher Tortoises:
Correct Answer: c. Increase in the number of alleles at a locus due to mutation
Explanation: In small populations, the primary concerns are genetic drift leading to fixation of alleles (including deleterious ones), potential for an extinction vortex, and habitat loss. Mutation rates are generally too low to significantly increase allele numbers in short time frames.
Relationship Between Genotype and Phenotype:
Correct Answer: a. Differences in gene expression lead to unique cells types in the body; all of these cells have the same genotype
Explanation: This statement accurately reflects how different gene expressions (phenotypes) can occur in cells that have the same genetic makeup (genotype). The other options are either incorrect or not directly related to the genotype-phenotype relationship.