Genetics Final Exam Quick Review

How many chromosomes do we have?

46 with 23 pairs

What is our diploid number?

46

What is our haploid number?

23

Meiosis

Reduces amount of genetic material by half

Produces haploid gametes or spores, each containing one member of a homologous pair of chromosomes

Crossing Over/Recombination

Meiotic event

Genetic exchange between members of homologous pairs of chromosomes

Meiosis: When does DNA Replication take place?

S phase

Meiosis: How many times is DNA replicated in a typical cell?

Once

What does Meiosis look like? (what order?)

Stages of Meiosis 1: prophase 1, metaphase 1, anaphase 1, telophase 1

Stages of Meiosis 2: prophase 2, metaphase 2, anaphase 2, telophase 2

Meiosis: prophase 1

homologous chromosomes pair up (tetrads) and crossing over occurs

Meiosis: metaphase 1

tetrads line up and spindle fibers attach to the centromeres

Meiosis: anaphase 1

chromosomes are pulled apart to opposite poles of the cell

Meiosis: telophase 1

cell divides into 2 haploid daughter cells that each contain one set of chromosomes

Meiosis: prophase 2

chromosomes condense again, spindle fibers form and attach to centromeres

Meiosis: metaphase 2

chromosomes line up along metaphase plate

Meiosis: anaphase 2

sister chromatids are separated and pulled to opposite poles of the cell

Meiosis: telophase 2

cells divide and result in 4 non-identical haploid daughter cells

What is a bivalent?

a pair of homologous chromosomes

When does crossing over occur?

Prophase 1

Does crossing over occur between sister chromatids or non-sister chromatids?

non-sister chromatids

What is a chiasma?

point where two non-sister chromatids of homologous chromosomes cross and physically link during meiosis

Are genes that are close together more or less likely to have a recombination event occur between them?

Less likely

At the end of mitosis, you end up with _________ daughter cells

two genetically identical

At the end of meiosis, you end up with ___________ cells (gametes).

four genetically unique haploid

What is non-disjunction?

the failure of chromosomes or sister chromatids to separate properly during cell division (meiosis or mitosis), resulting in daughter cells with an abnormal number of chromosomes (aneuploidy)

Exs. Down Syndrome, Turner Syndrome, and Klinefelter Syndrome

What does Mitosis look like? (order?)

interphase, prophase, metaphase, anaphase, telophase, cytokinesis

Mitosis: interphase G1 phase

cells grow and synthesize necessary proteins for DNA replication

Mitosis: interphase S phase

DNA is replicated and results in 2 sister chromatids

Mitosis: interphase G2 phase

cells continue to grow and prepare for mitosis

Mitosis: prophase

DNA coils into chromosomes, spindle fibers form

Mitosis: metaphase

chromosomes line up in the middle of the cell

Mitosis: anaphase

chromosomes are pulled apart

Mitosis: telophase

two new nuclear membranes form around the separated DNA

Mitosis: cytokinesis

cell divides into 2 identical daughter cells

Chromosomes, in diploid organisms, provide…

basis for biparental inheritance

Alleles

different versions of genes

Particulate unit factors (genes)

Basics of heredity

Passed unchanged from generation to generation

Determine various traits expressed by each individual plant (Mendel)

Mendel’s Postulates

1. Unit factors exist in pairs

2. Dominance/Recessiveness

3. Segregation

1. 2 copies of each gene, one from mom, one from dad

2. genes exist as alleles- one can be dom and another recessive

3. alleles segregate independently (bc chromosomes segregate independently)

What is a genotype?

an organism's complete set of inherited genetic instructions (DNA), often described as the specific combination of alleles (gene versions) for a particular trait

What is a phenotype?

the observable physical or functional trait that results from the genotype interacting with the environment

What does homozygous mean?

having two identical alleles (gene versions) for a specific trait, one inherited from each parent (DD, dd)

What does heterozygous mean?

having two different alleles of a particular gene or genes. (Dd)

What is the typical F2 phenotypic ration for a monohybrid cross?

3:1

How is a dihybrid cross different from a monohybrid cross?

A monohybrid cross studies inheritance of a single trait, while a dihybrid cross studies two traits simultaneously

What kind of bonds form the sugar phosphate backbone of DNA?

Phosphodiester bonds (covalent)

What kind of bonds form between bases on opposite strands?

Hydrogen Bonds

What are the 4 bases of DNA and RNA?

ATGC

AUGC

What bases complement and bond?

A - T(or U) and G - C

What base pair forms the stronger bond?

G - C (three hydrogen bonds)

DNA has polarity, runs in 5’ to 3’ direction. Do you remember what

gives it that polarity?

Because DNA is negative it runs towards the positive

Do the two strands run parallel or antiparallel?

antiparallel

Are the two DNA strands complementary or identical?

complementary

What is a nucleosome?

the fundamental building block of chromatin, consisting of a segment of DNA tightly wrapped around a core of eight histone proteins (an octamer), resembling "beads on a string" and allowing DNA to be efficiently packaged within the cell's nucleus

What are histones?

any of a group of basic proteins found in chromatin

When in the cell’s life is DNA highly compacted and when is it relaxed?

Compacted: Cell Division

Relaxed: Interphase

What modifications make DNA more compact? Relaxed?

Compact: involves histone methylation (H3K9me, H3K27me) and DNA methylation, creating dense heterochromatin

Relaxed: occurs via histone acetylation, phosphorylation (like KAP-1), and removal of methyl marks, loosening chromatin (euchromatin) for gene access

Are chromosomes completely uniform?

No, they vary in size

What makes up the bulk of our chromosomes?

long strand of DNA tightly wrapped around spool-like proteins called histones, forming structures called nucleosomes that coil further into chromatin, and finally condense into visible chromosomes during cell division

What is PCR?

Polymerase Chain Reaction

uses heat instead of helicase to separate DNA to find genetic sequences

What is the enzyme used in PCR?

Taq DNA Polymerase

How is PCR different from replication in the cell?

(in vitro) selectively amplifies specific DNA segments using temperature cycles and Taq polymerase

What are primers and how do they work?

short, synthetic DNA sequences that act as starting points for DNA copying, binding to opposite ends of a target DNA segment, while the DNA polymerase enzyme extends from their 3' ends to create new, complementary strands, exponentially amplifying the desired DNA sequence

What is epistasis?

masking the expression of one or more genes (non-mendelian inheritance)

Ex. Auguti

What is codominance?

when both alleles in a heterozygote are fully and separately expressed (like AB blood type)

What is incomplete dominance?

when the heterozygous phenotype is a blend or intermediate of the two homozygous parents (like red and white flowers making pink flowers)

Multiple alleles

occur when a gene has more than two versions (alleles) in a population (ABO blood group system)

Lethal alleles

mutated gene versions that cause an organism's death, usually early in development, by disrupting essential functions

Ex. Huntington’s Disease

Gene Linkage

the tendency for genes located close together on the same chromosome to be inherited together (less likely separated by crossing over)

Sex linkage

genes located on the sex chromosomes (X or Y) that are inherited along with them, causing a trait to be expressed differently in males and females

What is the enzyme that copies the DNA?

DNA Polymerase

What are primers in DNA Replication?

short, single-stranded DNA or RNA pieces that provide a crucial starting point for DNA polymerase to synthesize new DNA, acting like "platforms" that bind to a specific template sequence to kick off replication

DNA Replication: What is the enzyme that makes primers?

DNA Primase

How is the double helix unzipped?

Helicase

What are Okazaki fragments?

short, newly synthesized DNA segments that form on the lagging strand during DNA replication

What enzyme joins the Okazaki fragments?

DNA Ligase

What is the central dogma?

DNA -> RNA -> Protein

Does the double helix need to be unzipped for transcription?

Yes

What enzyme makes mRNA?

RNA Polymerase

Does transcription require primers?

No because RNA polymerase can initiate RNA synthesis directly from a DNA promoter sequence.

What is the job of the general transcription factors? (GTFs)

are crucial proteins that help start gene transcription by assembling a complex at a gene's promoter, guiding RNA polymerase II (Pol II) to the correct starting point on the DNA, unwinding the DNA, and stabilizing the entire initiation machinery, ensuring genes are accurately and efficiently turned "on" to make RNA

What is a promotor?

a specific DNA sequence, usually upstream of a gene, that acts as the "on switch" and binding site for RNA polymerase and transcription factors, telling them where to start making an RNA copy (transcription) of the gene, thus controlling its expression

Where is the TATA box?

Promoter region, 25-35 bp

What are the 3 major mRNA modifications that occur before an mRNA leaves the nucleus and can be translated?

5' capping, 3' polyadenylation, and RNA splicing

What are exons and introns?

intron - non-coding, does not get translated
exon - coding, gets translated

What is a codon?

a sequence of three consecutive nucleotides (bases like A, U, G, C) in a DNA or RNA strand that acts as a code unit, either specifying a particular amino acid (the building block of proteins) or signaling the start or end of protein synthesis

What’s the start codon?

AUG

What are the stop codons?

UAA, UAG, and UGA

Some can some can’t (crucial modifications on 5’ cap)

What is the organelle that does translation?

Ribosome

What makes up this organelle? (ribosome)

rRNA and various proteins

What kind of bond connects amino acids in the growing polypeptide

chain?

Strong Peptide Bonds

What adaptor molecule brings the amino acid to the mRNA?

tRNA

Aminoacyl synthetases attach amino acids to these adaptor

molecules. How many synthetases are there?

20

What is a frame shift?

a genetic mutation caused by adding or removing nucleotides (bases) in a DNA sequence that are not in multiples of three, shifting the entire "reading frame" for the ribosome, leading to completely different, often non-functional, proteins downstream from the mutation

What is a transcription factor?

proteins that control gene expression by binding to specific DNA sequences and regulating when and how genes are turned on or off

Describe enhancers vs activators

Enhancers - DNA sequences that boost gene expression

Activators - the proteins that bind to enhancers (or promoters) to make this happen

Describe silencers vs repressors (regulatory proteins)

Repressors - proteins that bind to DNA (operators/silencers) to block RNA polymerase, turning genes off, like in the lac operon.

Silencers - specific DNA sequences, often distant from the gene, that act as binding sites for these repressor proteins, causing long-range looping to inhibit transcription, effectively reducing or stopping gene activity in eukaryotes

Are enhancers and silencers always close to the promoter in eukaryotes?

No

Do eukaryotes have operons?

No, usually in prokaryotes

What is an operon?

“genetic switch”

a functional unit of DNA in prokaryotes (like bacteria) containing a cluster of related genes, a single promoter, and an operator, all controlled by one regulatory mechanism, allowing the cell to turn these genes on or off together for efficient resource management, like when processing a specific food source

What histone modification is likely to increase gene expression?

acetylation