BSCI222 Final Cumulative Topics

Topics that were missed from study guide

Histone

Histones: Organize DNA into nucleosomes 

Nucleosomes

Nucleosomes: 8 histone ball proteins and DNA

Chromatin

Chromatin: All DNA and histone proteins in the nucleus

Draw the metacentric, submetacentric, acrocentric, and telocentric positions.

What Enzymes are involved in Prokaryotic DNA replication?

• Prokaryotes

  • Helicase: Unzips the DNA

  • Gyrase: Relieves torsional strain 

  • Primase: Makes RNA using DNA template 

  • DNA pol III: Adds DNA to the 3’ end of the primer 

  • DNA pol I: Replaces the RNA primer with DNA

  • Ligase: Joins the nicks 

What Enzymes are involved in Eukaryotic DNA replication?

• Helicase: Unzips DNA

• Topoisomerase: Relieves torsional strain 

• DNA pol alpha: Puts down some RNA primer and synthesizes a small part of the DNA 

• DNA pol delta: Synthesises of the lagging strand 

• DNA pol epsilon: Synthesises of the leading strand 

• FEN1: Replaces the RNA primer portion with DNA

• DNA ligase: Joins the nicks

snRNA

snRNA: snRNA helps cut out introns from pre-mRNA (helps form the spliceosome). 

Promoter

DNA sequence that signals the start of transcription, location where RNA polymerase binds

Explain elements of the Prokaryotic promoter.

Explain elements of the Eukaryotic promoter.

Briefly, describe transcription in Prokaryotes.

Briefly, describe transcription in Eukaryotes.

What post-transcriptional modifications occur in Eukaryotes?

Alternative Splicing

Makes different combinations of exons —> more than 1 protein to be coded by mRNA

Prokaryotic Translation Initiation vs Eukaryotic Translation Initiation

Helix-turn-Helix

Bind to major groove of DNA

Operons are found only in ______. They have 4 elements _________.

Prokaryotes

P: Promoter (RNA Polymerase recruited and binds here)

R: Repressor (Can supress transcription if bound to operator)

O: Operator (where repressor binds, determines if transcription will occur

G: Gene

Inducible Operon. What is the function of the inducer?

Repressible Operon

Attenuation

Early termination of transcription

siRNA

Part of RISC complex that targets RNA

Dicer

Enzyme that cuts double stranded RNA

Linked Genes

Genes located together on the same chromosome tend to be inherited together

• Not 9:3:3:1 ratio

Recombinant Frequency

# of Recombinant/Total Offsprings

Cis vs Trans Configuration

Cis: Same alleles linked (DOM/DOM) or (REC/REC)

Trans: 2 different alleles linked (DOM/REC)

Coupling vs Repulsion

Double Crossover is the _______.

Parental or non-recombinant type _______.

Double Crossover is the least frequent.

Parental or non-recombinant type is the greatest.

Mitosis

Prophase

• Chromosomes condense

• Spindle fibers form

Mitosis

Prometaphase

Nuclear envelope disintegrates, and spindle microtubules attach to kinetochores.

Mitosis

Metaphase

Spindle captures all chromosomes and lines them up at the middle (metaphase plate)

Mitosis

Anaphase

Sister chromatids pulled to opposite ends

Mitosis

Telophase

Spindle disassembles, 2 new nuclei form, nuclear membrane reappears. Chromosomes decondense (stringy form)

Cytokenesis

Pinch crease disappears and 2 identical daughter cells are made.

Meiosis 1

Meiosis 2

Prophase 2: Haploid chromosomes condense

Metaphase 2: Chromosomes line up at the metaphase plate

Anaphase 2: Separation of sister chromatids

Telophase 2: 4 Haploid cells form

How many chromatids per chromosome will you find at each phase of Mitosis, Meiosis 1, and Meiosis 2?

What is reduction division in meiosis 1?

Diploid (2n) —> Haploid (1n)

Pure Breeding

Homozygous for either (Dominant AA) or (Recessive aa)

Mendel’s First Law: Principle of Segregation

Alleles for a gene will be separated into different gametes of equal proportion

Mendels Second Law: Principle of Independent Assortment

Alleles of one gene sort into the gametes independently of the alleles of another gene

Backcross

F1 Hybrid crossed back with parent

Testcross

Used to determine the unknown genotype of a dominant phenotype (AA vs Aa)

Crossing the individual with a homozygous recessive organism

• If offspring have recessive, then unknown genotype is heterozygous dominant

Monohybrid Cross

A cross between two organisms that are heterozygous (hybrid) for a single gene (Aa x Aa)

Yields 3:1 ratio

Dihybrid Cross

A cross following two different genes simultaneously, where both parents are hybrids (heterozygous) for both traits.

Expected Ratio: 9:3:3:1

(AaBb X AaBb)

What is the SRY gene? How does the SRY gene contribute to XX-XY sex determination? 

SRY gene is a Y-linked gene and determines whether an individual will develop as a male.

In mammals, all embroyos start with both male and female reproductive ducts with undifferentiated gonads. The SRY protein induces testes development and testosterone --> promoting male characteristics.

If SRY gene is absent (meaning no Y), an individual will undergo female development and male ducts will degenerate.

Chromosomal Sex Determination

ZZ-ZW

Chromosomal Sex Determination

XX-XO

Haplodiploid Sex Determination

Genic Sex Determination

Sex is determined by specific genes that regulate sexual development rather than by chromosome ratios or environmental conditions.

Environmental Sex Determination

A system in which an organism’s sex is determined by environmental conditions during development, rather than by sex chromosomes.

Environmental Sex Determination

Temperature Dependent Sex Determination

Organism’s sex is determined by the temperature experienced during embryonic development, rather than by sex chromosomes.

Environmental Sex Determination

Sequential Hermaphrodism

Individuals can change sex in their lifetime due to hormonal, social, or environmental signals.

Autosomal Dominant

Autosomal Recessive

X-Linked Recessive

X-Linked Dominant

What is the role of cohesion at the centromere?

Keep chromatids attached after DNA replication and during metaphase. At anaphase, cohesin is cleaved, allowing sister chromatids to separate and move to opposite poles.

Dosage Compensation

Explain random X-inactivation. What are barr bodies?

X-Inactivation: One of the two X chromosomes in female mammals is randomly turned off (inactivated) in each cell early in embryonic development.

Barr Body: Inactivated X chromosome that appears as a condensed, darkly staining body in the nuclei of most cells of female placental mammals.

Without regulation, females would produce twice as much X-linked gene product, which would disrupt normal development.

👉 X-inactivation provides dosage compensation, ensuring males and females have similar levels of X-linked gene expression.

Y-Linked Traits

Define incomplete dominance and provide an example.

Define co-dominance and provide an example.

Define complete dominance and provide an example.

What is haploinsufficiency? Use this as an example to describe how dominance works.

• Heterozygotes have the recessive phenotype

One copy does not have enough protein to express a trait. The heterozygote (Aa) looks more phenotypically like the recessive because the big A makes half the needed protein, and the little a makes no protein, which shows the recessive phenotype instead.

What is dominant negative? Use this as an example to describe how dominance works.

The mutant protein interferes with the function of the normal protein. Mutant disrupts everything, making the heterozygote express the mutant phenotype. So the mutant allele acts as the dominant.

Explain the difference between penetrance vs expressivity.

Define pleiotropy. What actions does it have?

One gene affects many traits

What are multi-genic traits?

Epistasis. Describe an example.

Diploid

Homologous pairs for every chromosome

2n

Haploid

One copy of each chromosome n=__

Explain nondisjunction. When does it happen? What is it? What type of cells are made?