Flashcards AGRI 3000 Exam 1

Norman Borlaug's contribution to the Green Revolution and its significance

He helped lead the GR by developing high-yield, disease-resistant wheat. His work increased food production and helped prevent famine for an est. one billion people.

Structures/organelles unique to an animal cell

No cell wall, no chloroplast, no large central vacuole

Structures/organelles unique to a plant cell

Has cell wall, chloroplasts, and a large central vacuole

Structures/organelles unique to a prokaryotic cell

No nucleus, no membrane-bound organelles, pro=simple

Nucleus

The control center of a eukaryotic cell. It stores DNA and controls gene expression.

Nuclear envelope

Surrounds nucleus; controls what enters/exits

Nucleoplasm

Fluid inside the nucleus

Chromatin

DNA + proteins; contains genes

Nucleolus

Makes rRNA and assembles ribosomal subunits

How does the nucleus regulate genes?

Controls which genes are turned on/off through chromatin organization

Where does transcription occur?

Nucleus

What happens during RNA processing?

5' cap, intron removal, exon joining, poly-A tail

What does the nucleus do during cell division?

Replicates and organizes DNA so chromosomes are properly distributed

Chromatids

Two identical copies of a chromosome joined together after DNA replication

Centromere

CENTRO= center; a region that holds sister chromatids together; spindle fibers attach here

Telomere

TELO= ends; protective ends of chromosomes; prevent DNA damage/loss

Euchromatin

EU= Easy to access; access; loosely packed DNA; genes are usually active/expressed

Heterochromatin

HETERO= Hidden; tightly packed DNA; genes are usually inactive/not expressed

Metacentric

META= Middle; centromere is in the middle; arms are about equal

Acrocentric

ACRO= Almost end; centromere is near one end; one short arm and one long arm

Telocentric

TELO= Totally end; centromere is at the very end; one arm

Gene

Segment of DNA at a specific locus that codes for a trait

Allele

Alternative version of a gene at that same locus

Locus

Location of a gene on a chromosome

Genotype

The specific allele combination an organism carries (e.g. Gg)

Phenotype

The observable trait that results (e.g. green seed color)

Homozygous

Two identical alleles at a locus (GG or gg)

Heterozygous

Two different alleles at a locus (Gg)

Haploid (n)

One set of chromosomes; found in gametes (sperm/egg)

Diploid (2n)

Two sets of chromosomes; one set from each parent

Corn's haploid (n)/diploid (2n) number

(n)=10 chromosomes (2n)=20 chromosomes

Interphase

Prepares cell for mitosis

G1 phase

Cell grows and performs normal functions

S phase

DNA is duplicated

G2 phase

Cell grows more and prepares for cell division

M phase

Mitosis + cytokinesis: nucleus divides, then cells split

Sister chromatids: how and when they form

One chromosome copies its DNA and forms during the S phase of interphase

PMAT

Prophase, Metaphase, Anaphase, Telophase

Prophase

Chromosomes condense, nuclear envelope breaks down, and spindle fibers form

Metaphase

Chromosomes line up in the middle of the cell

Anaphase

Sister chromatids separate and move to opposite sides

Telophase

Two new nuclei form around chromosomes and begin to uncoil

Genetic significance of mitosis

It produces two genetically identical daughter cells

How does mitosis maintain genetic material?

DNA is copied before mitosis, then sister chromatids are separated equally between the two daughter cells

Why does meiosis produce haploid and genetically variable cells, unlike mitosis?

Meiosis has two divisions, reducing chromosome number to haploid (n), and creates genetic variation through crossing over and independent assortment

Meiosis I

Reductional division: separates homologous chromosomes; produces 2 haploid cells

Prophase I

Homologous chromosomes pair up; crossing over occurs

Metaphase I

Homologous pairs line up in the middle

Anaphase I

Homologous chromosomes separate

Telophase I

Two haploid cells form

Meisosis II

Equatorial division: separates sister chromatids; produces 4 haploid cells

Prophase II

Spindle forms; chromosomes condense

Metaphase II

Chromosomes line up in the middle

Anaphase II

Sister chromatids separate

Telophase II

Four haploid cells form

LZPDD

Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis

Leptonema (Leptotene)

Chromosomes condense into long, thin visible threads

Zygonema (Zygotene)

Synapsis occurs; homologous chromosomes pair

Pachynema (Pachytene)

Crossing-over occurs; bivalents shorten and thicken as synapsis completes, exchanging DNA and creating genetic variation

Diplonema (Diplotene)

Homologs start to pull apart, but chiasmata remain

Diakinesis

Chromosomes condense further; nuclear envelope and nucleolus break down

Synaptonemal complex

A protein/DNA scaffold; holds homologs together

Bivalent

Paired set of homologous chromosomes (4 chromatids total)

Chiasma (plural: chiasmata)

X-shaped point where two chromatids physically cross

Crossing-over

Non-sister chromatids exchange segments

Recombinant chromosome

Chromosome containing a new combination of alleles created by crossing-over

Genetic recombination

Creation of new combinations of genetic material, increasing genetic variation

Why is meiosis important?

Maintains chromosome number and creates genetic diversity through independent assortment and crossing-over

Mendel's three postulates that explain transmission genetics

Segregation, independent assortment, and dominance

Segregation

Paired factors segregate during gamete formation at random, so each gamete recieves only one form

Indepdent Assortment

When two or more trait pairs are considered together, each pair assort into gametes independently of the others

Dominance

One trait is expressed to the exclusion of the alternative trait present in one of the parents

Qualitative

Distinct categories (e.g. flower color)

Quantitative

Measurable values with continuous variation (e.g. height, weight)

Monohybrid cross (Aa x Aa)

3:1 phenotype, 1:2:1 genotype

Dihybrid cross (AaBb x AaBb)

9:3:3:1 phenotype

Linkage

Certain genes tend to be inherited together

Complete linkage

Genes are very close together on the same chromosome and are inherited together; no crossing-over occurs between them

Incomplete linkage

Genes are on the same chromosome, but crossing-over can separate them, producing recombinant offspring

Coupling (cis)

One chromosome carries both dominant alleles (AB), the other both recessive (ab)

Repulsion (trans)

One chromosome carries one of each (Ab), the other the opposite (aB)

Chi-Square Test

Χ² = Σ (O − E)² / E

If calculated Χ² is below the critical value: the data is consistent with your expected ratio

If calculated Χ² exceeds the critical value: something (often linkage) is skewing the ratio

Incomplete dominance + F1/F2 outcomes

The heterozygote shows a phenotype intermediate between the two homozygotes (blended; red + white = pink)

F1: 100% intermediate

F2: 1:2:1 phenotype + genotype

Codominance + F1/F2 outcomes

Both alleles in a heterozygote are fully expressed

F1: 100% both traits expressed

F2: 1:2:1 phenotype + genotype

How does zygosity determine predictable breeding outcomes (e.g. roan horse coat color)

The roan coat color is incomplete dominance, so the heterozygous has its own distinct phenotype

Oligogenic inheritance

OLIGO=few, a trait that is controlled by a few genes

Polygenic inheritance

POLY=many, a trait that is controlled by many genes, often producing continuous variation

Epistasis

When one gene affects or masks the expression of another gene

Complementary action

(work together) Two genes both required for one effect

Modifying action

(changes) One gene's effect depends on another

Inhibiting action

(stops) One gene blocks a second gene's effect

Masking action

(hides) One gene hides a second gene's effect

Duplicate action

(each do the same thing) Either gene alone produces the same effect

Additive action

(add up) Two genes' effects combine when both present

Pleiotropic effect

One gene affecting multiple traits

Similarities between DNA and RNA

Both are nucleic acids made of nucleotides and contain genetic information

DNA

Deoxyribose sugar, A-T-C-G, double-stranded, stores genetic information

RNA

Ribose sugar, A-U-C-G, single-stranded, helps make proteins and regulate genes

C-value

The amount of DNA in one haploid genome

C-value paradox

That correspondence is not reliable—genome size does not track complexity