Genetics Exam 1 (Chapters 1-4, 11, 12)

What is the genetic material of all living cells?

DNA

What are the monomers of DNA and RNA called?

nucleotides

What is the 3 part structure of a nucleotide?

Sugar, phosphate, nitrogenous base

Which nitrogenous bases are purines?

Adenine & Guanine

Which nitrogenous bases are pyrimadines?

Cytosine, Thymine, Uracil

How is a 1’ carbon identified?

The nitrogenous base is attached (aka who is holding the fanciest thing).

How is the 3’ carbon identified?

The OH (hydroxyl) group is attached

How is the 5’ carbon identified?

The P (phosphate) group is attached

What is the difference between a nucleotide and nucleoside?

Nucleoside = sugar + base
Nucleotide = sugar + base + phosphate

What kind of bonds are found between nucleotides on the same strand?

Phosphodiester bond

What kind of bonds are found between DNA strands?

Hydrogen bonds

How many hydrogen bonds do A & T share?

2

How many hydrogen bonds do G & C share?

3

Which end of a strand has the phosphate group?

5’

Which end of a strand has the OH (hydroxyl) group?

3’

Who are credited with the discovery of the DNA double helix?

James Watson, Francis Crick & Rosalind Franklin

What did James Watson & Francis Crick contribute to the discovery of DNA’s structure?

They developed the DNA double-helix model.

What did Rosalind Franklin contribute to the discovery of DNA’s structure?

X-ray images showed DNA’s shape and helped reveal the double helix.

State the 4 major structural differences between RNA and DNA.

DNA:
Double-stranded
Deoxyribose sugar
Uses Thymine
A, T, G, C nucleotides

RNA:
Single-stranded
Ribose sugar
Uses Uracil
A, U, G, C nucleotides

What did Griffith discover?

Transformation = traits from dead bacteria could transfer to living bacteria.

What did Avery, MacLeod & McCarty discover?

DNA causes transformation → DNA is the genetic material.

What did Hershey & Chase discover?

DNA, not protein, enters bacteria → confirming DNA carries genetic information.

How did Griffith → Avery, MacLeod & McCarty → Hershey & Chase prove DNA is genetic material?

Griffith: discovered transformation
→ Avery, MacLeod & McCarty: identified DNA as the cause
→ Hershey & Chase: confirmed DNA carries genetic information

Describe the 5 key features of bacterial chromosomes

-circular
-double-stranded DNA
-usually one main chromosome
-located in the nucleoid
-supercoiled to fit inside the cell

What is the nucleoid?

the area of a bacterial cell where its chromosome is located; does NOT have a membrane around it like a nucleus

What is DNA supercoiling?

Twisting and coiling DNA to make it more compact.

What are the effects of DNA supercoiling?

Helps DNA fit inside the cell and affects how accessible the DNA is.

What is the second step of supercoiling called?

Macrodomain loops

What is the third step of supercoiling called?

Microdomain loops

What does a positive supercoil look like/mean?

Tighter DNA

What does a negative supercoil look like/mean?

Looser DNA

Describe the 9 general features and organization of eukaryotic chromosomes:

-linear
-found in the nucleus
-made of DNA + proteins
-DNA wraps around histones to help package the chromosomes
-100s to 1000s of genes per chromosomes
-multiple origins of replication
-centromeres (waists)
-telomeres (ends of the strands)
-repetitive sequences

Define chromatin

DNA + proteins that make up chromosomes (naked DNA + histones)

Define euchromatin

Loosely packed DNA - genes are more accessible/active

Define heterochromatin

tightly packed DNA - genes are less accessible/inactive

Describe the general structure of a nucleosome

DNA wrapped around a group of histone proteins

What are the 4 histone proteins found in the core histone?

H2A
H2B
H3
H4

How many of each histone protein are located in the core octamer?

2 of each of the 4 types

Which protein is the linker histone?

H1 (the pin that holds DNA to the octamer)

What are the roles of the core histone vs the linker histone?

Core histones - DNA wraps around them
H1 - helps hold/package the DNA between nucleosomes

Describe the general structure of the 30-nm fiber

A more tightly packed form of chromatin formed when nucleosomes coil/fold together (euchromatin).

What is repetitive DNA?

DNA sequences that are repeated many times.

What are the 2 main types of repetitive DNA?

Tandem repeats

Interspersed repeats

What are tandem repeats? What are the 3 types?

Repeats next to each other.

-Satellite DNA
-Minisatellites
-Microsatellites

What are interspersed repeats? What are the 2 types?

Repeats scattered throughout the genome.

-SINEs
-LINEs

What is a gamete?

A haploid (N) sex cell used for sexual reproduction.

What are examples of male and female gametes?

Sperm = male gamete

Egg/ovum = female gamete

What organisms produce gametes?

Animals, plants, fungi, and many protists.

Bacteria do NOT produce gametes.

What is a somatic cell?

Any body cell that is not a sex cell (gamete).

What are examples of somatic cells, and are they haploid or diploid?

Skin, muscle, nerve, and liver cells.

Usually diploid (2N).

What is spermatogenesis?

Production of sperm

What are the general steps of spermatogenesis?

Diploid germ cell → DNA replicates → Meiosis I → Meiosis II → 4 haploid sperm

What separates during Meiosis I vs. Meiosis II?

Meiosis I: homologous chromosomes separate

Meiosis II: sister chromatids separate

What is oogenesis?

Production of eggs (ova).

What are the general steps of oogenesis?

Diploid germ cell → DNA replicates → Meiosis I & II → unequal division → 1 large haploid egg + polar bodies

What is the main difference between spermatogenesis and oogenesis?

Spermatogenesis: 4 haploid sperm

Oogenesis: 1 large haploid egg + polar bodies

What is a true breeder?

An organism that produces offspring with the same trait for many generations.

What is the P generation?

The original parents in a genetic cross.

What is the F1 generation?

The offspring of the P generation.

What is the F2 generation?

The offspring of the F1 generation.

What does progeny mean?

Offspring

What is a dominant allele?

An allele that is expressed when present.
Written with an uppercase letter (P).

What is a recessive allele?

An allele that is masked by a dominant allele.

Written with a lowercase letter (p).

If purple (P) is dominant over white (p), what color are PP, Pp, and pp?

PP = purple

Pp = purple

pp = white

What is the Law of Segregation?

Your 2 alleles for a gene separate during meiosis, so each gamete gets only 1 allele.

Example of the Law of Segregation: What gametes can Aa make?

A or a

What happens to chromosomes during the Law of Segregation?

Homologous chromosomes separate during Meiosis I, separating their alleles.

What is the Law of Independent Assortment?

Alleles of different genes are distributed independently into gametes.

Example of Independent Assortment: What gametes can YyRr make?

YR, Yr, yR, yr

What is a single-factor (monohybrid) cross?

A genetic cross that follows 1 gene/trait.

Example: Pp × Pp

What is a two-factor (dihybrid) cross?

A genetic cross that follows 2 genes/traits.

Example: YyRr × YyRr

What is the classic phenotypic ratio of a dihybrid cross?

9 : 3 : 3 : 1

What is a genotype?

The allele combination an individual has for a gene.

Examples: PP, Pp, pp

What does homozygous mean?

Having 2 of the same alleles.

Examples: PP or pp

What is homozygous dominant vs. homozygous recessive?

PP = homozygous dominant

pp = homozygous recessive

What does heterozygous mean?

Having 2 different alleles.

Example: Pp

Does “dominant” mean an allele is more common?

No. Dominant means the allele is expressed when present, not that it is common.

Can a dominant allele be rare and a recessive allele be common?

Yes. Dominant/recessive describes expression, not frequency in a population.

What is a phenotype?

An organism’s expressed/observable traits.

What determines phenotype?

Genotype + environment

What are the 3 types of phenotypes?

Physical = appearance

Physiological = how the body functions

Behavioral = how it behaves

What are examples of physical, physiological, and behavioral phenotypes?

Physical: flower color

Physiological: number of eggs produced

Behavioral: mating dance

How many alleles for each gene does a gamete receive?

1 allele per gene

What gametes can AA produce?

A only

What gametes can Aa produce?

A or a

What gametes can aa produce?

a only

What gametes can AaBb produce?

AB, Ab, aB, ab

How do you find gametes for a genotype with 2 genes?

Take 1 allele from each gene and make all possible combinations.

What is the product rule in genetics?

Multiply the probabilities of independent events happening together.

How do you use the product rule for multiple genes?

Solve the probability for each gene separately → multiply them together.

Using the product rule: In TtYy × TtYy, what is the probability of ttyy?

In TtYy × TtYy, what is the probability of ttyy?

If the probability of aa = 1/4, bb = 1/4, and cc = 1/4, what is the probability of aabbcc?

1/4 × 1/4 × 1/4 = 1/64

Define sex chromosomes:

chromosomes involved in sex determination and may also carry other genes

Define autosomes

chromosomes that aren’t sex chromosomes

How does the XY sex-determination system work?

Female = XX

Male = XY

In the XY system, which parent determines whether offspring gets X or Y?

The male.

Egg = X only

Sperm = X or Y

What organisms use the XY system?

Humans, most mammals, and some plants.

What is the SRY gene?

Sex-determining Region Y gene.

Located on the Y chromosome and promotes testis/male development.

What is the XO/X-to-autosome system?

A sex-determination system used by many insects.

Sex can depend on the number/ratio of X chromosomes to autosomes.

Important: In fruit flies, the Y chromosome does NOT determine sex.