Biol 251 Exam 1

Prokaryotes

have no nucleus, are relatively small, contain circular genome DNA, have 1 chromosome, and typically have no membrane bound organelles.

Eukaryotes

have a nucleus, are relatively big, contain linear genome DNA, have multiple chromosomes and typically have membrane bound organelles.

Types of Prokaryotes

Bacteria and Archaea, which are unicellular organisms without a nucleus.

Nucleoid

DNA does not exist in the highly ordered and packed arrangement, and have a single orgin of replication that is not enclosed by a membrane.

Types of Eukaryotes

Fungi, Plants, Animals and Protists

Histones

Are proteins that help package and order DNA into structural units called nucleosomes, playing a crucial role in gene regulation and chromatin structure.

What is the Nuclear Envelope?

The double membrane structure that surrounds the nucleus in eukaryotic cells, separating the contents of the nucleus from the cytoplasm.

What happens in the Nuclear envelope?

The genetic material is strongly packed which causes them to start coiling. DNA is closely associated with histones to form tightly packed chromosomes.

Prokaryotic cells divide by doing

binary fission, a simple process where the cell replicates its DNA and divides into two identical daughter cells.

Binary Fission

-Replication Begins at the origin of replication.

• Double stranded DNA, circular chromosomes

-The chromosome is duplicated

-Two orgins of replication move to opposite sides of the cell.

-SMC complexes prevent tangling.

• SMC: Structural Maintenance of Chromosomes

- New cell wall forms

• Ends in two identical cells / Carbon copies of the parent cell (daughter cells)

Eukaryotic cells divide by performing

mitosis and meiosis, processes that involve the segregation of duplicated chromosomes and can lead to the formation of two identical cells or four non-identical gametes, respectively.

Homologous Chromosomes

chromosomes that are similar in size and structure

What do homologous chromosomes carry?

They carry genetic information for the same set of characteristics.

• There is one set of chromosomes from each parent.

How many pairs of chromosomes does a human have?

A human has 23 pairs of chromosomes.

How many sets of chromosomes does a diploid organism have>

A diploid organism has 2 sets of chromosomes.

Centromere

attachement point fr spindle microtubles

• the kinetichore is also here and directs the microtubles where to pull to seperate the chromosomes correctly in formation.

Telomeres

tips of a linear chromosome

• They continue to get shorter and shorter with each replication of your chromosomes, they degrate over time.

Origins of Replication

Location where DNA synthesis begins.

Sister chromatids

two copies of chromosomes that are held together at the centromere.

How do you count chromosomes?

By the centromeres.

Cohesin

is a protein that holds the chromatids together.

• protects from breakdown enzymes, and is important in mitosis.

Shugoshin

protects cohesin so sister chromatids stay together.

• acts as abd extra layer of protection, is important in making gametes.

What are the steps in Interphase?

G1, G1/S, S, G2, G2/M checkpoint

G1 phase

growth and proteins for the cell division is synthesized.

G1/S phase

regulated decision point.

(heartcells and neurological cells are made in G0)

S phase

DNA synthesis

G2 phase

Biochemical preparation for cell division

G2/M checkpoint

only passes if DNA is completely replicated and undamaged.

Mitosis

Seperation of sister chromatids

• separating individual DNA molecules

Prophase

chromosomes condense to form two chromatids.

• miotic spindles form from the centrosomes.

Prometaphase

The nuclear membrane breaks down.

• spindles attach to the chromatids at the kinetochore.

Kinetochore

directs the mircrotubles where to pull to separate chromosomes correctly in formation.

Metaphase

(middle) chromosomes align in the center of the cell.

• cohesin begins to break down.

Anaphase

sister chromatids separate and move to poles

• spindle polls = centrosomes

Telophase

nuclear membrane reforms and chromosomes decondense.

• preparing to split into two cells

Cytokenisis

-Seperation of cytoplasm

-results in full mitosis

• Two genetically identical cells that are identical to parent cells.

-cells have full compliment of chromosomes.

-each daughter cell has half of the cytoplasm.

Synapsis

Close pairing of homologous chromosome.

• When we have close association of homologous chromosomes and carry the same alleles.

Tetrad

Closely associated four-sister chromatids of homologous chromosomes.

Crossing Over

crossing over of chromosome segment from the sister chromatid of one chromosome to the other sister chromatid of the other synapsed chromosome.

• leads to geetic variation in mitosis.

Meiosis I

production of haploid gametes that create genetic variation.

• halfing the number of chromosomes.

Prophase I

the nuclear membrane breaks down

• crossing over occurs following condensation of chromosomes and homologous chromosomes pairing.

Metaphase I

Homologous pairs randomly align at center of the cell

Anaphase I

-shugoshin protects cohesin

-homologous chromosomes separate

-they then move towards the poles

Telophase I

• Cytoplasm separates after chromosomes move to poles.

• Nuclear membrane begins to reform

• Chromosomes decondense

  (cells still 2N)

Meiosis II

a type of cell division that creates gametes, or sex cells, for sexual reproduction.

Interkenisis

Nuclear membrane reforms and decondense

Prophase II

• Nuclear membrane breaks down

• Chromosomes condense

• Spindle fibers begin to form

Metaphase II

• Spindle Fibers Attach

• Individual chromosomes begin to align at center of each cell.

(at this point there have already been two cells)

Anaphase II

• Shogoshin breaks down

• Cohesin Breaks down

• SIster chromatids separate

Telophase II

• Chromosomes move to poles

• Nuclear membrane reforms

Cytokenisis (Meiosis II results)

• Four daughter cells have formed from one parent cell.

• Number of chromosomes in daughter cells is half of parent cell.

• Each daughter cell is genetically unique

  • crossing over and independent assortment

Comparing Mitosis and Meiosis

Mitosis

-synapsis

Meisosis I

-crossing over

-homolohous chromosomes

Interkenisis

Meiosis II

-4 daughter cells

-Prometphase II

-Metaphase II

-Anaphase II

-Telophase II

Mitosis and Meiosis I

-prophase

-prometaphase

-anaphase

-telophase

Mitosis and Meiosis II

-Seperation of sister chromatids (anaphase)

-One set of chromosomes at metaphase.

Meiosis I and Meiosis II

-Independent assortment

-Shegoshin

Mitosis, Meiosis I and Meiosis II

-Interphase

-Cytokenisis

-Cell Division

-PMAT (prophase, metaphase, anaphase, and telophase)

-Cohesin

How genetic variation in gamete occurs during meiosis

crossing over (genetic recombination), where homologous chromosomes exchange DNA segments during prophase I, and independent assortment, where chromosomes randomly align at the metaphase plate, leading to different combinations of alleles in the resulting gametes. 

Determine how many chromosomes, chromatids, or homologous chromosomes are in a cell

A typical human cell contains 46 chromosomes which are organized into 23 pairs of homologous chromosomes, meaning each cell has 23 homologous chromosome pairs; after DNA replication, each chromosome consists of two sister chromatids, resulting in a total of 92 chromatids in a cell. 

Key points:

• Chromosomes: 46

• Homologous chromosome pairs: 23

• Chromatids (after DNA replication): 92

Mendelian Genetics

refers to certain patterns of how traits are passed from parents to offspring.

Mendels model organisms characteristics

There are 5 characteristics

• Easy to use in lab

• Fast life cycle

• Genetic background is known

• Are genetically diverse

• Produce lots of offspring

Mendels Study approach

• Pea Plants studying seven characteristics

  • Binar characteristics

• Conducted crossses of plants for 7 years

• Hypothis based testing

Gene

inheritd genetic material that codes for trait

Allele

Different version of a gene (1 or 2)

Locus

Location of gene on chromosome

Genotype

Genetic make up ( AA, Aa, aa)

Phenotype

physical expression of trait

Homozygous

two of same alleles (AA, aa)

Heterozygous

two of different alleles (Aa)

What do alleles contain?

Alleles contain DNA sequence

• MRNA —> Protein —> Phenotype

DNA sequence codes for the protein/enzyme.

Mendels Principles of Heredity

the principle of segregation, the principle of dominance, and the principle of independent assortment.

Monohybrid

organisms differ in one trait

Principle of Segregation

each individual diploid organism passes two alleles for a characteristic.

• Two alleles segregate when gametes are formed

• One allele goes into each gamete

Concept of Dominance

when two different alleles are present in a genotype.

• Only the trait encoded by one of them is observed in the phenotype.

Dihybrid Cross

parents differ in two traits

Principle of independent assortment

gene do not influence each other during sorting of alleles into gametes.

• Every possible combination of alleles for every gene is equally likely to occur.

Probability

Likelihood of the occurance of a particular event.

• can be used to predict outcomes of crosses.

Multiplication Rule

probability of two or more independent events taking place together.

• Multiply independent probability

Addition Rule

probability of any of two or more mutually exculsive events.

• Calculated by adding the probabilities of the events

Binomial Expression

p = probability of having the recessive trait

q = probability of having the dominant trait

n = number of offspring

Example of Dihybrid Cross

Chi-Square Test

• Indicates the probability that the difference between the observed and expected values is due to chance

Formula: x²=∑ (observed count from cross - expected count based on punnet square)² / expected count based on punnet square

∑ is the sum of terms

x² is letter chi

Degrees of Freedom

number of independent random variables involved.

• number of phenotypes of offspring minus 1

  • n-1

Critical values of chi-square

p=0.05 is the threshold value in the table

• a result is said to not differ significantly froom expectations if it could happen by chance at least 5% of the time.

• if p>0.05 accept null hypothesis

• if p<0.05 reject null hypothesis

Example Chi-Square Test

Sex determination

the process by which an organism develops into a male or female

Sex

Sexual Phenotype

• Most organisms have two sexual phontypes

  • Males = small, inexpensive gametes

  • Female = large, expensive gametes

Gender

Category assigned by the individual or other based on behavior and cultural practices.

• Does not have to do with biological sex

Monoecious

both male and female reproductive structure present in an individual.

Dioecious

Individual has either male or female reproductive structures.

Chromosomal Sex Determination

the process where an individual's sex is determined by the combination of sex chromosomes they inherit.

XY System

Female: XX ← Homogametic

Male: XY ← Heterogametic

During meiosis sex chromosomes seperate equally into gametes.

XO System

Female: XX ← Homogametic

Male: XO ← Heterogametic

During meiosis only ½ of sperm cells get and X chromosome.

ZW System

Female: ZW ← Heterogametic

Male: ZZ ← Homogametic

During meiosis sex chromosomes separate equally into gametes.

Genic sex determination

Genotypes at one or more loci determine the sex of an individual.

• Plants

• Fungi

• Protists → Kelp

• Fishes

Environmental sex determination

a mechanism where an individual's sex is determined by environmental factors experienced during development, rather than by genetic inheritance. 

Sequential Hermaphroditism

Each individual animal can be both male and female.

Genic Balance sex determination

X: A Ratio: number of X chromosomes divided by the number of haploid sets of autosomes.

Indirect effect of X: A ontiming of development

XX AAA 0.67 intersex

XO AAA 0.33 metamale

Sex Determination Disorders

Non-disjunction dirung meiosis

• Turners syndrome

• Klinefeller Syndrome

• Poly-X Females

• XYY Males

Sex-Linked Characteristics

characteristics determined by geenes located on the sex chromosomes.

X-Linked Colorblindness

Gene for red and green cones is on the X chromosome,

normal vision female (X⁺X^c) cross Noraml vision male (X⁺Y)

Z-Linked characteristics

traits that are passed down through the Z chromosome. Because females have only one Z chromosome, Z-linked traits are always expressed in females.

Y-Linked characteristics

Females can never have the characteristics only males.

Dosage Compensation

Mechanism to equalize the amount of protein produced by X-Linked genes and autosomal genes.

Sex Chromosomes are either “balanced” or “imbalanced” with autosomes.

• Males produce less proteins for genes on X chromosomes.

Lyon Hypothesis

Brarr Bodies: inactivated X chromosomes that appear as a condensed, darkly staining body in the nuclei.

• Most placental mammals exhibit this.