Biology Syllabus

What happens during crossing over, and in which phase does it occur?

Crossing over is the exchange of homologous segments between non-sister chromatids of paired homologous chromosomes, occurring during prophase I of meiosis. It increases genetic variation through recombination.

State Mendel's Law of Segregation.

Mendel's Law of Segregation states that the two alleles for each trait separate (segregate) during gamete formation, so each gamete carries only one allele for each gene; the alleles reunite at fertilization.

State Mendel's Law of Independent Assortment.

The Law of Independent Assortment states that alleles of different genes assort independently of one another during gamete formation, so the inheritance of one trait does not affect the inheritance of another (for genes on different chromosomes).

Distinguish between genotype and phenotype.

Genotype is the genetic makeup (allele combination) of an organism, e.g., $Tt$; phenotype is the observable physical or biochemical expression of that genotype, e.g., tall.

Distinguish between homozygous and heterozygous.

Homozygous means having two identical alleles for a gene (e.g., $TT$ or $tt$); heterozygous means having two different alleles for a gene (e.g., $Tt$).

In a monohybrid cross between two heterozygotes ($Tt \times Tt$), what are the expected genotypic and phenotypic ratios?

The expected genotypic ratio is $1\,TT : 2\,Tt : 1\,tt$, and the phenotypic ratio is $3$ dominant : $1$ recessive.

What phenotypic ratio is expected from a dihybrid cross between two heterozygotes ($TtRr \times TtRr$)?

A dihybrid cross between two heterozygotes yields a phenotypic ratio of $9:3:3:1$ for the four combinations of the two traits.

Differentiate between incomplete dominance and codominance.

In incomplete dominance the heterozygote shows a blended intermediate phenotype (e.g., red $\times$ white = pink); in codominance both alleles are fully and simultaneously expressed in the heterozygote (e.g., AB blood type).

What is a test cross and why is it used?

A test cross is a cross between an organism showing the dominant phenotype (unknown genotype) and a homozygous recessive organism. It is used to determine whether the dominant individual is homozygous or heterozygous based on the offspring.

What is the chemical structure of DNA according to Watson and Crick?

DNA is a double helix of two antiparallel polynucleotide strands. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base. The strands are held together by hydrogen bonds between complementary base pairs.

State the base-pairing rules in DNA and the number of hydrogen bonds in each pair.

In DNA, adenine pairs with thymine via 2 hydrogen bonds ($A=T$), and guanine pairs with cytosine via 3 hydrogen bonds ($G\equiv C$). In RNA, thymine is replaced by uracil ($A$ pairs with $U$).

What is a chromosome, and how many do humans have?

A chromosome is a threadlike structure of tightly coiled DNA wrapped around histone proteins, carrying genetic information. Humans have 46 chromosomes (23 pairs), including 22 pairs of autosomes and 1 pair of sex chromosomes.

Define a gene and an allele.

A gene is a segment of DNA that codes for a specific protein or functional RNA and determines a trait. An allele is one of two or more alternative versions of a gene at a given locus.

Describe the central dogma of molecular biology.

The central dogma describes the flow of genetic information: DNA is transcribed into RNA, and RNA is translated into protein. Symbolically: $\text{DNA} \to \text{RNA} \to \text{Protein}$.

What occurs during transcription, and where does it take place in eukaryotes?

Transcription is the synthesis of a complementary mRNA strand from a DNA template by RNA polymerase. In eukaryotes it occurs in the nucleus, and the mRNA is then processed and exported to the cytoplasm.

What occurs during translation, and what is a codon?

Translation is the synthesis of a polypeptide from an mRNA sequence at the ribosome, with tRNA delivering amino acids. A codon is a sequence of three mRNA nucleotides that specifies a particular amino acid or a stop signal.

How does the lac operon illustrate gene regulation in prokaryotes?

The lac operon is a cluster of genes for lactose metabolism controlled by a single promoter. When lactose is absent, a repressor binds the operator and blocks transcription; when lactose is present, it inactivates the repressor, allowing transcription. This is an example of inducible gene regulation.

What is a gene mutation, and name three point mutation types.

A gene mutation is a change in the DNA nucleotide sequence. Three point (substitution) mutation types are: silent (no amino acid change), missense (one amino acid changed), and nonsense (codon changed to a stop codon).

How do insertion and deletion mutations cause a frameshift?

Insertion or deletion of nucleotides (not in multiples of three) shifts the reading frame of the codons downstream of the mutation, altering every subsequent amino acid and often producing a nonfunctional protein.

What is the difference between somatic and germline mutations?

Somatic mutations occur in body cells and are not passed to offspring (they may cause cancer); germline mutations occur in reproductive (gamete) cells and can be inherited by offspring.

Summarize Darwin's theory of evolution by natural selection.

Darwin proposed that organisms vary, more offspring are produced than can survive, and individuals with favorable heritable variations are more likely to survive and reproduce. Over generations, these advantageous traits become more common, leading to evolution of populations.

What are the four conditions necessary for natural selection to occur?

Natural selection requires: (1) variation among individuals, (2) heritability of that variation, (3) overproduction of offspring leading to competition, and (4) differential survival and reproduction (differential fitness).

Define biological fitness in evolutionary terms.

Biological fitness is an organism's relative ability to survive and produce viable, fertile offspring that contribute to the next generation's gene pool. Higher fitness means a greater genetic contribution to future generations.

Distinguish among directional, stabilizing, and disruptive selection.

Directional selection favors one extreme phenotype, shifting the mean; stabilizing selection favors intermediate phenotypes and reduces variation; disruptive selection favors both extremes against the intermediate, potentially splitting the population.

What is speciation, and what is the most common mechanism in animals?

Speciation is the formation of new, distinct species from existing ones through reproductive isolation. The most common mechanism in animals is allopatric speciation, where a population is geographically separated and diverges over time.

Differentiate between allopatric and sympatric speciation.

Allopatric speciation occurs when populations are geographically separated, leading to divergence; sympatric speciation occurs within the same geographic area through reproductive isolation mechanisms such as polyploidy or behavioral differences.

Distinguish between homologous and analogous structures.

Homologous structures share a common evolutionary origin but may differ in function (e.g., human arm and bat wing), indicating divergent evolution; analogous structures have similar function but different evolutionary origins (e.g., bird wing and insect wing), indicating convergent evolution.

What is the fossil record, and what does it reveal about evolution?

The fossil record is the chronological collection of preserved remains and traces of past organisms in rock layers (strata). It provides evidence of evolution by showing the sequence, age, and transitional forms of organisms over geological time.

What is a transitional fossil? Give a classic example.

A transitional fossil shows intermediate features linking ancestral and derived groups. A classic example is Archaeopteryx, which has both reptilian features (teeth, clawed digits, bony tail) and avian features (feathers, wings), linking dinosaurs and birds.

What is the main function of the digestive system, and where does chemical digestion of starch begin?

The digestive system breaks down food into absorbable nutrients, absorbs them into the blood, and eliminates waste. Chemical digestion of starch begins in the mouth, where salivary amylase breaks starch into maltose.

What is the role of the small intestine in digestion and absorption?

The small intestine is the main site of chemical digestion and nutrient absorption. Enzymes complete digestion, and its inner lining of villi and microvilli vastly increases surface area for absorbing nutrients into the blood and lymph.

Describe the pathway of air through the respiratory system and the site of gas exchange.

Air travels: nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli. Gas exchange occurs across the thin walls of the alveoli, where $\ce{O2}$ diffuses into the blood and $\ce{CO2}$ diffuses out.

Write the overall chemical equation for aerobic cellular respiration.

$$\ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O + ATP}$$ Glucose is oxidized using oxygen to release carbon dioxide, water, and energy stored as ATP.

Trace the path of blood through the human heart starting from the body.

Deoxygenated blood enters the right atrium → right ventricle → pulmonary artery → lungs (oxygenated) → pulmonary veins → left atrium → left ventricle → aorta → body. The right side handles deoxygenated blood and the left side handles oxygenated blood.

Compare arteries, veins, and capillaries by function.

Arteries carry blood away from the heart (usually oxygenated) under high pressure with thick walls; veins return blood to the heart (usually deoxygenated) under low pressure and contain valves; capillaries are thin, single-cell-walled vessels where exchange of gases, nutrients, and wastes occurs.

What is the difference between pulmonary and systemic circulation?

Pulmonary circulation carries deoxygenated blood from the heart to the lungs and returns oxygenated blood to the heart; systemic circulation carries oxygenated blood from the heart to the body tissues and returns deoxygenated blood to the heart.