Bio Final 1111

What is a gene?

A unit of heredity made of DNA that contains information to build a protein or functional RNA.

What are gametes?

Reproductive cells (sperm and egg) that carry genetic information to the next generation; haploid with 23 chromosomes.

What are somatic cells?

All body cells except gametes; diploid with 46 chromosomes.

What is a locus?

The specific physical location of a gene on a chromosome.

What are homologous chromosomes?

A pair of chromosomes with the same genes in the same order

How are homologous chromosomes alike?

Same length

What are autosomes?

The 22 pairs of chromosomes that are not involved in sex determination.

What are sex chromosomes?

Chromosomes that determine biological sex (X and Y).

Female sex chromosomes?

XX.

Male sex chromosomes?

XY.

What does diploid (2n) mean?

A cell with two sets of chromosomes (46 in humans).

What does haploid (n) mean?

A cell with one set of chromosomes (23 in humans).

Asexual reproduction definition

One parent passes all genes to offspring; offspring are genetically identical (clones).

Sexual reproduction definition

Two parents produce genetically unique offspring due to gene mixing.

What is fertilization?

Fusion of sperm and egg to form a zygote.

What is a zygote?

A fertilized egg cell that is diploid.

How do humans grow from a zygote?

Through mitosis producing somatic cells.

What is meiosis?

A two-step cell division that produces haploid gametes from diploid cells.

When does DNA replicate in meiosis?

During S phase before meiosis I.

How many divisions occur in meiosis?

Two: meiosis I and meiosis II.

How many cells result from meiosis?

Four haploid daughter cells.

Prophase I – key events

Homologous chromosomes pair (synapsis) and crossing over occurs.

What is synapsis?

Physical pairing of homologous chromosomes.

What is crossing over?

Exchange of DNA between homologous chromosomes creating new allele combinations.

What are chiasmata?

Visible crossover points where DNA is exchanged.

Metaphase I – key event

Homologous chromosome pairs line up at the metaphase plate.

Anaphase I – key event

Homologous chromosomes separate; sister chromatids stay together.

Telophase I result

Two haploid cells with duplicated chromosomes.

How is meiosis II similar to mitosis?

Sister chromatids separate.

Why aren’t sister chromatids identical in meiosis II?

Because crossing over occurred in meiosis I.

Final result of meiosis

Four genetically distinct haploid cells.

Mitosis produces…

Two genetically identical diploid cells.

Meiosis produces…

Four genetically different haploid cells.

Three sources of genetic variation

Independent assortment; crossing over; random fertilization.

Independent assortment definition

Each homologous chromosome pair aligns randomly at metaphase I.

Independent assortment formula

2ⁿ possible combinations (n = haploid number).

Random fertilization definition

Any sperm can fertilize any egg.

Why is genetic variation important?

Allows populations to adapt and survive environmental changes.

Why are monoclonal crops risky?

They lack variation which makes them vulnerable to disease or environmental shifts.

What is a mutation?

A permanent change in an organism’s DNA that creates new alleles.

What is a point mutation?

A change in a single nucleotide pair.

Missense mutation

Changes one amino acid to another.

Silent mutation

Does not change amino acid due to redundancy in the genetic code.

Nonsense mutation

Converts an amino acid codon into a stop codon.

Frameshift mutation

Insertions or deletions that shift the reading frame.

Fitness effects of mutations

Beneficial (increase fitness); neutral (no effect); deleterious (decrease fitness).

Why can’t DNA polymerase finish the 5′ end?

It needs a 3′ OH group to add nucleotides.

What are telomeres?

Repetitive DNA sequences at chromosome ends that protect genes.

Role of telomerase

Extends telomeres in germ cells and cancer cells.

Proofreading

DNA polymerase removes incorrect nucleotides during replication.

Mismatch repair

Fixes base-pairing errors missed during proofreading.

Nucleotide excision repair

Removes damaged DNA segments and replaces them.

Central Dogma

DNA → RNA → Protein.

What is transcription?

Synthesis of RNA using DNA as a template.

Enzyme responsible for transcription

RNA polymerase.

Promoter definition

DNA sequence where RNA polymerase binds.

TATA box

Eukaryotic promoter sequence.

Transcription stages

Initiation

Polyadenylation signal

Signals RNA cleavage in eukaryotes.

What is translation?

Synthesis of a polypeptide at the ribosome.

Start codons

AUG

Stop codons

UAA

Complete dominance

Heterozygote looks like dominant homozygote.

Incomplete dominance

Heterozygote shows intermediate phenotype.

Codominance

Both alleles fully expressed.

Multiple alleles example

ABO blood group (IA

Pleiotropy

One gene affects multiple traits.

Epistasis

One gene masks or alters expression of another gene.

Polygenic inheritance

Multiple genes affect one trait (e.g.