Genetics and Evolution: Key Concepts for Biology Students

What are genes?

Genes code for proteins and are the units of inheritance passed from parents to offspring.

What are alleles?

Different versions of the same gene that arise from mutations.

What is a diploid cell?

A cell with a full set of chromosomes (two copies of each).

What is a haploid cell?

A cell with only one set of chromosomes (like sperm or egg).

What is a genotype?

The genetic makeup (alleles) of an organism.

What is a phenotype?

The observable physical traits expressed by genes.

Who is Gregor Mendel?

The scientist who studied inheritance (the passing of genetic information from parent to offspring) using pea plants—"father of genetics."

What does a Punnett square show?

Predicts possible genotypes and phenotypes of offspring.

Define homozygous dominant, recessive, and heterozygous.

AA = dominant, aa = recessive, Aa = heterozygous.

What is the F1 generation?

The first offspring generation from two parent organisms. It shows which traits are dominant

What is the F2 generation?

Offspring of the F1 generation, showing trait recombination. It shows how reappear or mix in new combinations

What is meiosis?

Cell division producing genetically unique haploid gametes.

Gemetes

Reproductive cells that unite during fertilization to form a new organism.

Haploid Cell

A cell that contains one complete set of chromosomes, typically a gamete.

Zygote

A diploid cell formed when two gametes unite during fertilization, which develops into an embryo.

What is recombination (crossing over)?

Chromosomes exchange DNA segments during meiosis I.

What is independent assortment?

Random distribution of chromosomes during meiosis I.

What is nondisjunction?

Failure of chromosomes to separate properly in meiosis.

What condition results from trisomy 21?

Down Syndrome. Have 3 copies (trisomy) of chromosome 21 (instead of 2)

Cystic Fibrosis

A recessively inherited genetic disease. Alterations to the CFTR protein cause disease by interfering with ion and water balance in cells, especially in the lungs.

What are sex chromosomes?

Chromosomes that determine biological sex (XX or XY).

What gene determines male development?

The SRY gene on the Y chromosome.

What is sex-linked inheritance?

Traits determined by genes on the X or Y chromosome.

What are X-linked traits?

Traits determined by alleles on the X chromosome (e.g., Duchenne muscular dystrophy).

What is a pedigree?

Diagram showing inheritance of traits across generations.

What is incomplete dominance?

Heterozygotes show a blend of traits.

What is codominance?

Both alleles are expressed equally.

What is a polygenic trait?

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

What are multifactorial traits?

Traits influenced by both genes and environment.

Define microevolution.

Gradual genetic change within a population over time.

Define macroevolution.

Large-scale changes leading to new species or extinction.

What is fitness?

The ability to survive and reproduce.

What is evolution?

Change in allele frequencies in a population over time.

What are two ways bacteria gain new alleles?

Random mutation and gene transfer.

What was the Harvard Mega-Plate experiment?

Showed bacteria evolving antibiotic resistance in real time.

What are the four conditions for evolution?

Heritability, genetic variation, fitness variation, and differential survival.

What is natural selection?

Process where organisms with advantageous traits reproduce more.

What are the three patterns of natural selection?

Directional (Predominant phenotype shifts in a particular direction), stabilizing (Phenotypes of population settle near the middle of range), and diversifying (Phenotypes of population are at both extremes of range).

What is sexual selection?

Evolution of traits that increase mating success.

What is reproductive isolation?

Barriers preventing species from interbreeding.

Name five prezygotic barriers.

Ecological (Live in different habitats/regions), temporal (Mating or fertile at different times), behavioral (Different mating behaviors), mechanical (Physical differences, mating organs incompatible), gametic (Sperm cannot fertilize egg).

Name two postzygotic barriers.

Hybrid inviability (Gametes unite but offspring not viable - die after fertilization) and hybrid infertility ( Offspring are infertile and cannot reproduce).

What is speciation?

Formation of new species due to genetic divergence.

What is genetic drift?

Random change in allele frequencies between generations.

What is the founder effect?

New population started by a few individuals.

What is the bottleneck effect?

Population reduced drastically, reducing diversity.

Why is genetic diversity important?

Increases adaptability to changing environments.

What increases genetic diversity?

Mutation, gene flow, and interbreeding.

What supports descent from a common ancestor?

Fossils, homologous structures, developmental similarities, vestigial traits, DNA evidence.

What is convergent evolution?

Similar traits evolve in unrelated species due to similar environments.

What caused Florida panther inbreeding issues?

Bottleneck effect and loss of gene flow.

How was the Florida panther population restored?

Interbreeding with Texas panthers increased genetic diversity.

What is melanin?

Pigment that protects skin from UV radiation.

Why is skin color correlated with UV exposure?

High UV = darker skin for protection; low UV = lighter skin for vitamin D production.

What type of evolution is skin color an example of?

Convergent evolution.

What are sex hormones and where are they produced?

Hormones produced by gonads (ovaries and testes).

Which hormones are classified as androgen hormones?

Estrogen and testosterone.

How do sex hormones influence fetal development?

They shape the development of sexual anatomy, depending on the fetus's inherited chromosomes.

How many pairs of chromosomes do humans have?

Humans have 23 pairs of chromosomes.

What are autosomes?

22 pairs of chromosomes that are present in both males and females.

How do sons inherit their sex chromosomes?

Sons inherit 1 Y chromosome from their father and 1 X chromosome from their mother.

How do daughters inherit their sex chromosomes?

Daughters inherit 1 X chromosome from their mother and 1 X chromosome from their father.

Continuous variation

is a type of genetic variation where traits are not just categorical but instead exist on a spectrum. Examples include height and skin color, which show a range of phenotypes.

Evolution

A change in allele species over time. The process by which species change over long periods of time through changes in their genetic traits.

What are the four conditions for evolution?

1. The trait is heritable.

2. Genetic variation in the trait within the population.

3. Variation in fitness within the population.

4. Individual fitness varies depending on the trait.

How do populations evolve by natural selection?

A population's inherited phenotype and environmental pressures determine the frequency of traits. If traits improve fitness, they become more common, leading to a change in allelic frequency and thus, the population evolves by natural selection.

Theory of Evolution

All species present on Earth today are descendants of a single common ancestor, and all species represent the product of millions of years of accumulated microevolutionary changes.

What was Charles Darwin's role in evolution?

Credited with bringing evolution to mainstream, modern science, proposing that living things have been diverging from a common ancestor since life originated, a concept known as "Descent with modification."

What is "Descent with modification"?

The idea that living things have been diverging from a common ancestor since life originated, through various processes.

What is "Darwinism"?

A term often applied to the theory of evolution.

What is Genetic Divergence

When populations of a species develop genetic differences over time.

What is the Gene Pool?

The total collection of all alleles in a population

Genetic Drift

 Change in allele frequencies between generations that occurs purely by chance.

What is the Founder Effect?

When a small group of individuals forms a new population, carrying only part of the original population’s genetic variation.

What is the Bottleneck Effect?

When a random event (like a natural disaster) drastically reduces a population, leaving only a small, random subset of survivors.

Why is genetic diversity important?

It gives a population flexibility to survive in a changing environment — the more genetic variation, the more ways it has to adapt.

What happens when a population gains genetic diversity?

It gains new alleles that increase adaptability and fitness.

What are three ways genetic diversity can increase?

• Mutation – random changes in DNA.

• Gene Flow – movement of alleles between populations.

• Interbreeding – mating between different populations or groups.

What is inbreeding, and why is it harmful?

Mating between closely related individuals; it increases the chance of harmful recessive traits appearing.

What does common ancestry mean?

Related organisms share similar DNA sequences due to descent from a shared ancestor.

What is convergent evolution?

When unrelated species develop similar traits due to living in similar environments.

What are five main types of evidence for descent from a common ancestor?

• Fossils – show physical changes over time.

• Homologous Structures – similar anatomy from a shared ancestor.

• Developmental Homology – similar embryonic development.

• Vestigial Structures – useless remnants of features once functional in ancestors.

• DNA Evidence – shared genes across different species.

What caused the Florida panther population to nearly go extinct?

Loss of gene flow, hunting, and a bottleneck effect reduced genetic diversity and survival rates.

What physical signs showed inbreeding among Florida panthers?

Kinked tail tips and unusual back fur patterns.

How did scientists restore the Florida panther population?

Introduced 20 female Texas panthers to interbreed, adding new alleles and increasing genetic diversity and fitness.

What is the current conservation status of Florida panthers?

They are now on the Least Concern list for endangered species.

What is melanin?

A pigment in skin cells that blocks UV radiation from damaging DNA.

What determines a person’s skin color?

The type and amount of melanin produced by their cells.

Why is skin color an example of convergent evolution?

Different populations developed similar skin tones in response to similar UV conditions, despite not being closely related.

Why did human skin color begin to vary?

As humans migrated out of Africa, populations became isolated and adapted to different sunlight levels on each continent.

How is skin color related to UV radiation?

Dark skin provides protection in high-UV regions, while light skin allows more UV to penetrate in low-UV regions for vitamin D production.

Why isn’t darker skin always favored?

In low-UV areas, lighter skin allows more UV to pass through, helping the body produce enough vitamin d.