EXAM 3

Binary Fission

Asexual reproduction in prokaryotes.

Single circular molecule

Typical form of DNA in prokaryotes.

Histones

Proteins that DNA wraps around in eukaryotes.

Cohesins

Proteins that hold sister chromatids together at the centromere.

G2/M checkpoint

Checkpoint that ensures DNA has been properly replicated and is damage-free before mitosis.

Metaphase plate

The alignment of chromosomes in a single-file line during metaphase.

Contractile ring

Structure in animal cells that forms the cleavage furrow during cytokinesis.

Cell plate

Structure in plant cells that leads to the formation of a new cell wall between daughter cells.

Heterozygous

A genotype with two different alleles.

Circular, maternally inherited DNA

Characteristic of organelles like mitochondria and chloroplasts.

Nucleoid region

Location of the circular genome in prokaryotes.

Plasmids

Small extrachromosomal circles of DNA in bacteria.

Histone and chromatin

Eukaryotic DNA wraps around histone proteins to form nucleosomes, which further coil to form chromatin.

Homozygous

A person with two identical alleles for a gene.

G1/S checkpoint

Checkpoint that checks for necessary enzymes and DNA damage before duplication.

S phase

Phase during which chromosomes are duplicated into sister chromatids.

Anaphase

Phase in which sister chromatids are pulled to opposite spindle poles.

Cleavage furrow

Structure formed in animal cells during cytokinesis by a contractile ring.

G1

Phase of the cell cycle associated with protein synthesis and cell growth.

Homologous chromosomes

Chromosomes that share the same genes but may have different alleles.

Cyclin availability

Factor that directly determines the next step in the cell cycle.

Cdk (Cyclin-dependent kinase)

Enzyme that phosphorylates target proteins leading to progression through the cell cycle.

Proto-oncogene

Type of gene that Cdk is classified as.

Oncogene

Result of a mutation that causes a proto-oncogene to become overactive.

p53

Protein that detects DNA damage and halts the cell cycle.

p21

Protein that inhibits the cyclin-Cdk complex when recruited by p53.

Rb (Retinoblastoma protein)

Protein that normally inhibits a transcription factor; when phosphorylated, it releases that inhibition.

Prophase I

Stage of meiosis when crossing over occurs.

Reduction division

Term for meiosis I, as it reduces ploidy from diploid to haploid.

Equational division

Term for meiosis II, as it separates sister chromatids without changing ploidy.

Independent assortment

Mechanism that causes interchromosomal variation during meiosis.

Telophase I

Stage at the end of meiosis I where two genetically variable haploid cells are formed.

Four haploid sperm

Final product of meiosis in human males.

One haploid secondary oocyte and one polar body

Final product of meiosis I in human females.

Diploid zygote

What is formed when a sperm fertilizes an egg.

Incomplete dominance

Condition where the heterozygous phenotype is an intermediate blend of the two alleles.

Codominance

Condition where both alleles in a heterozygote are fully expressed, such as in blood type AB.

Translocation mutation

Chromosome rearrangement that causes a gene to be placed under the control of a different promoter.

Aneuploidy

An abnormal number of a specific chromosome.

Trisomy 21

Condition caused by nondisjunction of chromosome 21, also known as Down syndrome.

X-inactivation

Process that helps prevent severe dosage problems for X-linked genes in biological females.

Nondisjunction in meiosis I

Results in two n+1 and two n-1 gametes.

Translocation

Structural mutation involving part of one chromosome moving to a non-homologous chromosome.

Recombination frequency of 33%

Indicates that genes are 33 map units apart on a chromosome.

5 centimorgans apart

Indicate tightly linked genes.

Dosage problems

Issues caused by an abnormal number of a specific chromosome that can lead to gene overexpression or underexpression.

Prokaryotes have a circular genome located in the _______.

Nucleoid region

Small extrachromosomal circles of DNA in bacteria are called ______.

Plasmids

Eukaryotic DNA wraps around ______ proteins to form nucleosomes, which further coil and condense to form ______ structures.

Histone, chromatin

The _________ checkpoint checks for necessary enzymes and DNA damage before duplication.

G1/S checkpoint

During the __ phase, chromosomes are duplicated into sister chromatids.

S phase

Cyclins activate ___________ (Cdks), which phosphorylate target proteins to move the cell cycle forward.

Cyclin-dependent kinases

If a proto-oncogene mutates to become overactive, it becomes an oncogene, which can lead to _______.

Cancer

Cdk inhibitors, such as ____, stop the cell cycle when conditions are not right for division

P21

The protein ___ either releases cell cycle arrest when DNA is repaired or triggers _______ if damage is beyond repair.

P53, apoptosis

The _______ normally inhibits a transcription factor, but when phosphorylated, it releases that inhibition, allowing the cell to pass the G1/S checkpoint.

Rb protein

______ of meiosis is when crossing over occurs between homologous chromosomes.

Metaphase l

Meiosis II is called an _______ because it separates sister chromatids without changing ploidy.

Equatorial division

Fertilization of the egg by a sperm forms a ______.

Diploid Zygote

In ____________, the heterozygous phenotype is an intermediate blend of the two alleles.

Incomplete dominance

In ________, both alleles in a heterozygote are fully expressed, such as in blood type AB.

Codominance