BISC 130 3-2

What is cancer?

Uncontrolled cell growth that causes harm to surrounding tissues and organs.

What usually causes uncontrolled cell growth?

Failures in cell cycle control proteins due to mutations.

What causes mutations in cell cycle control proteins?

Mutations in the genes that code for those proteins.

What causes mutations in DNA?

Unrepaired DNA damage.

What is a proto-oncogene?

A normal gene involved in the cell cycle that can become an oncogene when mutated.

What is an oncogene?

A mutated version of a proto-oncogene that can lead to cancer.

How can we prevent mutations that lead to cancer?

By repairing DNA damage with tumor suppressor proteins/genes.

What is the function of the p53 protein?

It detects DNA damage, brings in repair enzymes, and can trigger apoptosis if damage is too severe.

What happens if the gene for p53 is mutated?

The protein becomes non-functional, leading to unchecked cell division and increased risk of cancer.

What percentage of genetically studied cancers involve a p53 mutation?

About 50%.

Why is sexual reproduction important?

It increases genetic diversity, improving the chances of survival in changing environments.

What is the result of sperm (1n) + egg (1n)?

A diploid zygote (2n).

Why must sperm and eggs be haploid?

To ensure that when they combine, the resulting zygote has the correct diploid chromosome number.

What is meiosis?

A special type of cell division that produces haploid gametes (sperm and egg) from diploid cells.

Which cells undergo meiosis?

Germ cells in the testes and ovaries.

How many cells are produced by meiosis?

Four haploid cells.

What are homologous chromosomes?

Chromosomes with the same genes but slightly different DNA sequences. They are similar in structure but not identical, unlike sister chromatids.

What are sister chromatids?

Identical copies of a chromosome formed during DNA replication. They are exactly the same in sequence and structure.

What is synapsis?

The process during prophase I where homologous chromosomes pair up to form tetrads.

What is a tetrad?

A group of four chromatids (two homologous chromosomes, each made of two sister chromatids) formed during synapsis in prophase I.

What is crossover?

The exchange of genetic material between homologous chromatids, increasing genetic variation.

When does crossover occur?

During prophase I of meiosis.

Why is crossover important?

It creates new genetic combinations, contributing to genetic diversity in offspring.

What is the key event of metaphase I?

Tetrads align at the center of the cell with random orientation, leading to genetic variation.

What happens during anaphase I?

Homologous chromosomes (tetrads) are pulled apart, but sister chromatids remain together.

What is the ploidy of cells after meiosis I?

Haploid with replicated DNA (each cell has one set of chromosomes, each still consisting of two sister chromatids).

Is there a second interphase before meiosis II?

No. Cells enter meiosis II directly after cytokinesis I.

How is meiosis II similar to mitosis?

Each phase of meiosis II (prophase, metaphase, anaphase, telophase) mirrors the steps and function of mitosis.

What happens in anaphase II?

Sister chromatids are finally separated and pulled to opposite poles.

What is the end result of meiosis II?

Four genetically unique haploid cells, each with a single copy of each chromosome.

How many possible combinations of chromosomes are there in human gametes due to independent assortment alone?

Over 8 million combinations (2²³)