Ag Genetics Exam 1

What was Norman Borlaug’s contribution to the Green Revolution?

He developed high-yielding, disease-resistant wheat varieties that greatly increased crop production and helped reduce famine and food shortages worldwide.

Why was Borlaug’s work significant to agricultural genetics?

It demonstrated how genetic improvement of crops can increase yields, improve disease resistance, and help feed a growing population.

What is a prokaryotic cell?

A cell that does not have a nucleus or membrane-bound organelles. Bacteria and archaea are prokaryotes.

What is a eukaryotic cell?

A cell that has a nucleus and membrane-bound organelles. Animal and plant cells are eukaryotic.

What structures are unique to plant cells compared with animal cells?

Cell wall, chloroplasts, and a large central vacuole.

What is the function of the plant cell wall?

Provides support, protection, and shape to the cell.

What is the function of chloroplasts?

They carry out photosynthesis, converting light energy into chemical energy.

What is the function of the large central vacuole?

Stores water, ions, nutrients, and waste and helps maintain pressure within the plant cell.

What structures are found in animal and plant cells but NOT prokaryotes?

A nucleus and membrane-bound organelles, such as mitochondria, ER, and Golgi apparatus.

What structure is found in both prokaryotic and eukaryotic cells?

Both have a cell membrane, cytoplasm, ribosomes, and DNA.

What is a major difference between prokaryotic and eukaryotic DNA?

Prokaryotic DNA is generally located in a nucleoid region rather than inside a nucleus.

What is the function of the nucleus?

It stores DNA and controls gene expression and many activities of the cell.

What is the nuclear envelope?

A double membrane surrounding the nucleus that separates nuclear contents from the cytoplasm.

What are nuclear pores?

Openings in the nuclear envelope that control movement of molecules into and out of the nucleus.

What is nucleoplasm?

The fluid inside the nucleus in which chromatin and the nucleolus are suspended.

What is chromatin?

DNA associated with proteins, primarily histones, within the nucleus.

What is the nucleolus?

A region of the nucleus where rRNA is produced and ribosomal subunits are assembled.

How does the nucleus regulate genes?

It controls which genes are turned on or off, regulating which proteins the cell produces.

What is RNA processing?

The modification of newly made RNA, including 5' capping, splicing, and poly-A tail addition, before mature mRNA leaves the nucleus.

How does the nucleus coordinate cell division?

It replicates and organizes DNA into chromosomes and coordinates the distribution of genetic material during cell division.

What is a chromatid?

One of the two copies of a replicated chromosome

What are sister chromatids?

Two genetically identical copies of a chromosome joined together after DNA replication.

What is the centromere?

The region where sister chromatids are joined and where the kinetochore forms for chromosome movement during cell division.

What is a telomere?

A protective DNA sequence at the end of a chromosome that helps prevent chromosome ends from being damaged or incorrectly joined.

What is euchromatin?

Loosely packed chromatin that is generally more accessible for gene transcription

What is heterochromatin?

Tightly packed chromatin that is generally less accessible and contains many regions of low gene activity.

What is the difference between euchromatin and heterochromatin?

Euchromatin = loose and generally active. Heterochromatin = tightly packed and generally less active.

What is a metacentric chromosome?

A chromosome with the centromere approximately in the middle, producing arms of roughly equal length.

What is an acrocentric chromosome?

A chromosome with the centromere close to one end, producing one very short arm and one long arm.

What is a telocentric chromosome?

A chromosome with the centromere at or extremely close to the end, appearing to have essentially one arm.

What is a gene?

A segment of DNA that contains information for a functional product, such as a protein or functional RNA.

What is an allele?

A specific version of a gene.

What is a locus?

The specific location of a gene or DNA sequence on a chromosome

What is a genotype?

The genetic makeup of an organism, such as BB, Bb, or bb.

What is a phenotype?

The observable characteristics or traits of an organism, resulting from its genotype and environmental influences.

What does homozygous mean?

Having two identical alleles for a gene. Example: BB or bb

What does heterozygous mean?

Having two different alleles for a gene. Example: Bb

What is the difference between a gene and an allele?

A gene is the DNA sequence associated with a trait/function; an allele is a specific version of that gene.

What does haploid (n) mean?

Having one complete set of chromosomes.

What does diploid (2n) mean?

Having two complete sets of chromosomes, one set inherited from each parent

What are homologous chromosomes?

A pair of chromosomes, one inherited from each parent, that have the same genes at the same loci but may carry different alleles.

Are homologous chromosomes genetically identical?

No. They contain the same genes but can have different alleles.

What is the difference between homologous chromosomes and sister chromatids?

Homologous chromosomes come from different parents and may have different alleles. Sister chromatids are identical copies of the same chromosome made during DNA replication.

What are the two major parts of the cell cycle?

Interphase and the M phase.

What are the three stages of interphase?

G1, S, and G2.

What happens during G1 phase?

The cell grows, performs normal functions, and produces proteins and organelles.

What happens during S phase?

The cell replicates its DNA, creating two copies of each chromosome.

What happens during G2 phase?

The cell continues growing, makes proteins needed for cell division, and prepares for mitosis.

What is the M phase?

The phase in which the cell undergoes mitosis and cytokinesis, producing two daughter cells.

What happens during interphase overall?

The cell grows, carries out normal functions, replicates its DNA, and prepares for division.

What are sister chromatids?

Two identical copies of a chromosome that are joined together at the centromere.

When do sister chromatids form?

During the S phase of interphase, when DNA is replicated.

Why are sister chromatids genetically identical?

They are produced by copying the same DNA molecule during DNA replication.

When do sister chromatids separate?

During anaphase of mitosis

What happens to sister chromatids after they separate?

Each chromatid becomes an individual chromosome in one of the two daughter cells.

What are the four main stages of mitosis?

Prophase → Metaphase → Anaphase → Telophase (PMAT).

What happens during prophase?

Chromatin condenses into visible chromosomes, the mitotic spindle forms, and the nuclear envelope breaks down.

What happens during metaphase?

Chromosomes line up in the middle of the cell at the metaphase plate.

What happens during anaphase?

Sister chromatids separate and are pulled toward opposite ends of the cell.

What happens during telophase?

Chromosomes reach opposite poles, new nuclear envelopes form, and chromosomes begin to decondense.

What is cytokinesis?

The division of the cytoplasm, producing two separate daughter cells.

Does cytokinesis occur during mitosis?

It generally overlaps with or follows telophase, but it is technically separate from mitosis.

What is the main genetic purpose of mitosis?

To produce two genetically similar daughter cells with the same chromosome number as the parent cell.

How does mitosis maintain a constant amount of genetic material?

DNA is copied during S phase, and mitosis then separates the copies equally between the two daughter cells.

if a parent cell is diploid (2n), what will the daughter cells be after mitosis?

Both daughter cells will be diploid (2n).

How many daughter cells are produced by mitosis?

two

Are daughter cells produced by mitosis genetically identical?

They are generally genetically identical to the parent cell and to each other, aside from mutations that may occur.

Why is maintaining the chromosome number important?

It ensures that cells receive the correct amount of genetic information as an organism grows and replaces cells.

What is the main purpose of meiosis?

To produce haploid (n) gametes for sexual reproduction while creating genetic variation.

Why does meiosis produce haploid cells?

Because chromosome number is reduced by half during Meiosis I when homologous chromosomes separate.

Why is reducing chromosome number important?

When two haploid gametes fuse during fertilization, the diploid chromosome number is restored.

How is meiosis different from mitosis genetically?

Mitosis produces genetically similar diploid cells, while meiosis produces genetically variable haploid cells.

How many cells does meiosis produce?

Four haploid cells.

Why are the four cells produced by meiosis genetically different?

Because of crossing-over and independent assortment.

What is Meiosis I called?

The reductional division because chromosome number is reduced from diploid (2n) to haploid (n).

What does Meiosis I separate?

Homologous chromosomes.

What is Meiosis II called?

The equational division because chromosome number remains haploid.

What does Meiosis II separate?

Sister chromatids.

What is the major difference between Meiosis I and Meiosis II?

Meiosis I separates homologous chromosomes; Meiosis II separates sister chromatids.

What happens during Prophase I?

Homologous chromosomes pair up (synapsis), crossing-over occurs, chromosomes condense, and the spindle forms.

Why is Prophase I especially important?

It is when synapsis and crossing-over occur, creating genetic variation.

What happens during Metaphase I?

Homologous chromosome pairs line up in the middle of the cell.

What is independent assortment?

The random orientation of homologous chromosome pairs at Metaphase I, causing maternal and paternal chromosomes to be distributed into gametes in different combinations.

What happens during Anaphase I?

Homologous chromosomes separate and move toward opposite poles.

Do sister chromatids separate during Anaphase I?

No. Sister chromatids remain attached.

What happens during Telophase I?

Chromosomes reach opposite poles, and cytokinesis produces two haploid cells.

What happens during Prophase II?

Chromosomes condense, the spindle forms, and the nuclear envelope breaks down if it had re-formed.

What happens during Metaphase II?

Chromosomes line up individually in the middle of each cell.

What happens during Anaphase II?

Sister chromatids separate and move toward opposite poles.

What happens during Telophase II?

Nuclear envelopes form around the chromosomes, chromosomes decondense, and cytokinesis produces four haploid cells

What happens during leptonema?

Chromosomes begin to condense and become visible.

What happens to DNA before leptonema?

DNA has already been replicated during S phase, so each chromosome consists of two sister chromatids.

What happens during zygonema?

Homologous chromosomes begin synapsis, pairing closely with each other.

What structure helps homologous chromosomes pair during zygonema?

The synaptonemal complex.

What happens during pachynema?

Homologous chromosomes are fully paired, and crossing-over occurs between non-sister chromatids.

Why is pachynema important?

It is the major stage associated with crossing-over and genetic recombination.

What happens during diplonema?

Homologous chromosomes begin to separate from one another, but remain connected at chiasmata, the visible sites of crossing-over.

What becomes visible during diplonema?

Chiasmata.

What happens during diakinesis?

Chromosomes become highly condensed, chiasmata move toward chromosome ends, and the cell prepares for Metaphase I.

What is the synaptonemal complex?

A protein structure that forms between paired homologous chromosomes and helps hold them together during synapsis.