Final (copy)

Exam 3 | Gillespie review

What are the general purposes for cell division?

Mitosis: Reproduction, Growth + Development, Tissue renewal
Meiosis: Produce haploid gametes for reproduction

Describe the general activities that occur during the 3 parts of interphase?

Gap 1 -- normal growth
Synthesis -- chromosomes duplicated
Gap 2 -- Cell duplicates organelles and produces proteins for mitosis

What are the three key checkpoints in the cell cycle? What conditions must be met to proceed through each? Explain how cyclin and cyclin dependent kinase work to regulate those checkpoints?

G₁ checkpoint, G₂ checkpoint, M checkpoint

What conditions must be met to proceed through each checkpoint in the cell cycle?

G1: Is the cell large enough to enter the cycle?
G2: Have the chromosomes duplicated?*
M: Are all dyads attached to spindlefibers?

Explain how cyclin and cyclin dependent kinase work to regulate those checkpoints?

Checkpoint Checks for Cyclin: Cyclin protein + Cdk (kinase) → MPF (Maturation Promoting Factor)
Happens at G2 phase

What are the steps of mitosis? Describe the significant events affecting the nuclear membrane, chromosomes, centrosomes, and spindle fibers during each step.

Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis*
*happens with the latter stages of mitosis. NOT part of mitosis.

Prophase

Chromatin condense + visible
Spindle fibers synthesized
Nuclear membrane begins to dissolve

Prometaphase

Nuclear membrane dissolved
Centrosome almost at opposite poles
Kinetochore microtubules (spindle fibers) attach to dyads

Metaphase

Kinetochore microtubules push dyads to metaphase plate
Non kinetochore microtubules (also spindle fibers) grow + overlap

Anaphase

Monads migrate to opposite poles
use reeling model or pac man model

Reeling Method

Motor proteins pull on microtubules from centrosome end, Enzymes dissolve microtubules at centrosome end

Pac-Man method

Enzymes would dissolve microtubules from kinetochore end, while motor proteins "walk" the monat

Telophase

New nuclei membranes
Monads decondense
Microtubule breakdown

Cytokinesis (animal)

Contractile microfilaments made inside plasma membrane
initial contraction = cleavage furrow

Cytokinesis (plants)

Build new cell walls to divide daughter cells

Plant mitosis vs animal mitosis

Plants mitosis in meristem rapidly dividing areas to elongate tips of stem/root or expand width)
Animal mitosis throughout body

Plant cytoplasmic division = build cell wall
Animal cytoplasmic division - cleavage furrow

Explain the mechanism for the movement of chromosomes along the spindle fibers during anaphase?

Reeling Method, Pac Man Method

What is the purpose of meiosis and in what kinds of cells does it occur?

Produce haploid gametes for reproduction (eggs and sperms)

What are the steps of meiosis I and meiosis II? Describe the significant events affecting the nuclear membrane, chromosomes, centrosomes, and spindle fibers during each step.

prophase I → Metaphase I → Anaphase I → Telophase I + Cytokinesis I
prophase II → Metaphase II → Anaphase II → Telophase II + Cytokinesis II

Prophase I

Condense chromatin (dyads)
dissolve nuclear membrane
Assemble centrosomes + Spindle fibers
Homologous chromosomes come together (SYNAPSIS/ TETRADS)
monads can CROSS OVER

Cross over

happens at "chiasmata" randomly; recombinant chromosomes.

Metaphase I

Spindle fibers place tetrads along metaphase plate
Each dyad connected by spindle fiber
Alignment of dyads is independent for all pairs

Anaphase I

Motor proteins move dyads toward opposite poles

Telophase I + Cytokinesis I

DNA DOESN'T LOOSEN UP
NO NUCLEAR MEMBRANE
Breakdown of spindle fibers
Cytokinesis : split into 2 daughter cells (2n)

Prophase II

New spindle fibers and centrosomes form

Metaphase II

Dyads positioned along metaphase plate
Spindle fibers connected to monads

Anaphase II

Motor proteins move monads to opposite poles

Telophase II + Cytokinesis II

Chromosomes decondense
Spindle fibers disassemble
Nuclear membrane reformed
Cytokinesis splits cell into 2 haploid cells (n)

Describe two ways in which genetic variation arise from meiosis. What is crossing over and how does it occur?

Independent assortment of homologous chromosomes (Metaphase I)
Random fertilization of gametes
Crossing over (Prophase I) -- occurs at chiasmata where two homologous pairs exchange a portion of their chromatid

Why characteristics of pea plants made them ideal for Mendel experiments?

First wanted mice, but didn't want infestation
Chose peas because:
Easy to grow
Short generation time
Distinct varieties (flower color, pea color, pea shape, height)
Could be altered to show parentage

Explain the experiments Mendel performed which allowed him to develop the law of segregation and law of independent assortment.

segregation of alleles corresponds to distribution of homologous chromosomes to different gametes in meiosis, Mendel's segregation model accounts for the 3:1 ratio he observed in F₂ generation : Principle of segregation
Mendel saw peas that were yellow and round, or yellow and shrivelled, proving the principle of independent assortment

How can the law of segregation and independent assortment be used to explain variation among organisms?

Number of possible combinations of chromosomes at Metaphase I: 2ⁿ = 2²³ ≈ 8 million
Random combination of gametes possibility: 8 mill. × 8 mill. = 64 trill.

Gene

a sequence of nucleotides forming a part of a chromosome, the order of which determines the characteristics of the offspring. Basic unit of heredity

Allele

The different types of gene

Homozygous

Having two of the same alleles

Heterozygous

Inheriting two different alleles

dominant

Overshadows the recessive allele

Recessive

The phenotype that can be overshadowed by the dominant allele

Genotype

genetic makeup

Phenotype

characteristic/physical appearance

Compare and contrast complete dominance, incomplete dominance, and co-dominance and give an example of each types

Complete dominance - Mendel's peas: Can't tell het phenotype apart from dominant hom. phenotype
Incomplete dominance - Snapdragon: phenotypes different from parental generation, blending
Codominance - Blood type: not a blend, both fully dominant and present at the same time, separate but distinguishable

Define polygenic traits and give an example of one

individuals that vary in the population with many different phenotypes (height, skin color, etc.), controlled by multiple genes

Describe the phenomenon of epistasis and how it affects the expression of phenotypes.

A gene acts as an on/off gene for another gene.
Ex: albinism is epistasis for hair color

Explain how Mendel's principles of inheritance are supported by the behavior of chromosomes during meiosis. Be sure to address both the principle of segregation and the principle of independent assortment.

Principle of segregation: In meiosis anaphase 1, the homologous pairs are seperated. In anapahse II, the two sister chromatids are also seperated and by the end of meiosis end up in different daughter cells which proves Mende;'s principle of segregation that each parent only provides 1 allele to offspring. Since the tetrads align independent of maternal or paternal heritage along the metaphase plate in metaphase I, the principle of independent assortment is also true, that one gene 's alleles do not get passed down dependent on another gene's alleles (unless they are an exception, ofcourse. But Mendel worked with phenotypes that were luckily on different chromosomes so it does prove the theory in the way he was thinking about it).

Explain the experiment by T. H. Morgan that allowed him to support the hypothesis that genes are located on chromosomes

He breeded varieties of fruit flies that were distinct from natural populations.
First mutant: male with white eyes.
Breeded mutant white eye male with wild type red eye female →F1: all red eyes→ F2:all females had red eyes, ½ males had red eyes == gene on X chromosome
Showed how a specific gene is carried by a specific chromosome == proof

What are sex linked genes? How is sex determined in fruit flies and in humans? What are other ways of determining sex as demonstrated by other organisms?

Sec linked genes are genes that are passed down by sex cells (XY). Sex is determined in fruit flies and humans through XY. Other ways of determining sex is XO (grasshopper), ZW (chicken), Haplodiploid (bees)

Describe two examples of sex-linked genetic disorders in humans

Color blindness
Duchenne Muscle Dystrophy
Hemophilia B
Androgen insensitivity Syndrome

What are linked genes? Describe the experiment from Morgan's lab that demonstrated gene linkage

Genes on the same chromosome that are hence heredited together. Morgan's dihybrid cross of body type and wings showed 17% recombinant

What are recombinant chromosomes and how are they produced?

REcombinant chromosomes are chromosomes that are not genetically identical to the parent chromosomes. They are produced by crossing over.

Describe how recombination frequencies can be used to produce linkage map if given

[# of recombinant results]/[total # of results] * 100
1% =1 mapping unit