Genotype, Phenotype, and Evolution Study Guide

Genotype

The genetic makeup of an organism (e.g., AA, Aa, or aa).

Phenotype

The observable traits or characteristics resulting from the genotype (e.g., brown eyes, tall height).

Law of Segregation

Each individual has two alleles for a trait; these separate during gamete formation.

Law of Independent Assortment

Genes for different traits assort independently during meiosis.

Complete Dominance

One allele is fully dominant over the other (e.g., red flowers in RR vs. white in rr).

Incomplete Dominance

A blend of traits occurs in heterozygotes (e.g., red RR, white rr, and pink Rr flowers).

Codominance

Both alleles are expressed equally (e.g., blood type AB).

Polygenic Traits

Controlled by multiple genes (e.g., skin color, height).

Multifactorial Traits

Influenced by both genetics and environment (e.g., diabetes, heart disease).

Chromosomes

XX (female) or XY (male).

Gonads

Ovaries (female) and testes (male).

Hormones

Estrogen (female) and testosterone (male).

Genotype Crossing

Used to predict offspring genotypes from parental crosses (e.g., crossing Aa x Aa gives a 3:1 phenotypic ratio for dominant traits).

Sex-linked Inheritance

Traits found on sex chromosomes (usually X-linked).

Microevolution

Small-scale evolutionary changes within a population over generations.

Fitness

The ability of an organism to survive and reproduce in its environment.

Evolution

A change in allele frequencies in a population over time.

Harvard Mega-Plate Experiment

A visual demonstration of bacterial evolution and antibiotic resistance, showing adaptation over time.

4 Necessary Conditions for a Trait to Evolve

Variation: Individuals have different traits. Heritability: Traits must be genetic and passed to offspring. Differential Survival & Reproduction: Some traits provide a survival advantage. Time: Changes occur over multiple generations.

Natural Selection

Process where traits that enhance survival and reproduction become more common.

Directional Selection

Favors one extreme (e.g., larger beaks in finches).

Stabilizing Selection

Favors the average (e.g., human birth weight).

Diversifying Selection

Favors both extremes (e.g., light and dark moths, but not intermediate).

Sexual Selection

Traits that increase mating success (e.g., peacock feathers, antlers in deer).

Acquisition of New Alleles

Bacteria evolve resistance through mutations and gene transfer.

Species

A group of organisms that can interbreed and produce fertile offspring.

Population

A group of individuals of the same species living in the same area.

Macroevolution

Large-scale evolutionary changes leading to new species.

Theory of Evolution & Role of Charles Darwin

Darwin proposed descent with modification through natural selection.

Adaptive Evolution

Driven by natural selection, leading to beneficial traits.

Non-Adaptive Evolution

Caused by random processes like genetic drift.

Reproductive Isolation

Prevents different species from interbreeding.

Prezygotic Isolation

Before fertilization (e.g., behavioral, temporal, mechanical barriers).

Postzygotic Isolation

After fertilization (e.g., sterile offspring like mules).

Speciation

Formation of new species due to genetic isolation.

Genetic Drift

Founder Effect: A small group starts a new population with limited genetic diversity.

Bottleneck Effect

A population is drastically reduced (e.g., cheetah population decline).

Genetic Diversity

Increases survival chances.

Common Ancestry

Species share traits due to a common ancestor.

Convergent Evolution

Unrelated species develop similar traits (e.g., wings in bats and birds).

Evidence for Evolution

Fossils: Show transitional forms (e.g., whale ancestors with legs).

Homologous Structures

Similar anatomy due to shared ancestry (e.g., human arm & bat wing).

Developmental Homology

Similar embryonic development (e.g., vertebrates have gill slits in early stages).

Vestigial Structures

Useless remnants of past features (e.g., human tailbone).

DNA Evidence

Similar genetic sequences show relatedness (e.g., humans & chimps share ~98% of DNA).

Florida Panther Extinction

Genetic bottleneck due to habitat loss and low population numbers.

Biology of Skin Color

Evolutionary adaptation to UV radiation: Darker skin protects against UV damage, while lighter skin aids in vitamin D synthesis.

Evolution of Lactose Tolerance

Some human populations evolved the ability to digest lactose into adulthood due to dairy farming.