Genetics Comprehensive Review Flashcards

Comprehensive flashcards covering genome structure, mitosis, meiosis, Mendelian genetics, linkage, dominance, bacterial genetics, and transposable elements based on lecture transcripts. Note: Original set contained 360 units across chapters; the set has been expanded to meet final requirements.

What is a genome?

The complete set of DNA of an organism, including chromosome DNA and other genetic elements.

Besides chromosomes, what other DNA molecules can contribute to a genome?

Plasmids, organelle genomes (mitochondria/chloroplasts), and viral genomes.

Does a larger genome necessarily mean a more complex organism?

No.

What is a major difference between prokaryotic and eukaryotic chromosomes?

Prokaryotic DNA remains relatively compact while eukaryotic chromosomes undergo extensive condensation and decondensation.

How many double-stranded DNA molecules make up a chromosome?

$1$.

What is a centromere?

The chromosome region where sister chromatids are attached and spindle fibers connect.

What is a telomere?

The protective DNA sequence at chromosome ends.

What is the nucleolus?

The site of ribosome production inside the nucleus.

What is a nucleolar organizer region?

A chromosome region containing genes for rRNA production.

What is heterochromatin?

Highly condensed chromatin with low transcriptional activity.

What is euchromatin?

Loosely packed chromatin with high transcriptional activity.

Which is generally more transcriptionally active: heterochromatin or euchromatin?

Euchromatin.

Why are chromosome banding patterns useful?

They help identify chromosomes and chromosomal abnormalities.

Why do histones bind DNA well?

Histones contain positively charged lysine and arginine residues that interact with negatively charged DNA.

Which histones form the nucleosome core?

$H2A$, $H2B$, $H3$, and $H4$.

How many copies of each core histone are present in a nucleosome?

$2$.

What is a histone octamer?

Two copies each of $H2A$, $H2B$, $H3$, and $H4$.

What role does $H1$ play?

It helps stabilize DNA wrapping around nucleosomes.

What is a nucleosome?

DNA wrapped around a histone octamer.

Why are nucleosomes important?

They are the fundamental unit of chromatin packaging.

What occurs during $G_1$?

Cell growth and preparation for DNA replication.

What occurs during $S$ phase?

DNA replication.

What occurs during $G_2$?

Preparation for mitosis.

What occurs during $M$ phase?

Mitosis and cytokinesis.

What is $G_0$?

A non-dividing state outside the cell cycle.

In which phase are sister chromatids produced?

$S$ phase.

After DNA replication, how many chromatids does each chromosome possess?

$2$ sister chromatids.

What is the overall purpose of mitosis?

To produce genetically identical daughter cells.

During prophase, what happens to chromosomes?

They condense.

During prophase, what happens to the nucleolus?

It disappears.

During prophase, what happens to the nuclear envelope?

It breaks down.

What is a kinetochore?

A protein complex at the centromere where spindle fibers attach.

What align at the metaphase plate?

Chromosomes.

What separate during anaphase?

Sister chromatids.

What forms during telophase?

New nuclear envelopes.

What is cytokinesis?

Division of the cytoplasm.

If sister chromatids are separating, what stage is occurring?

Anaphase.

If chromosomes are aligned in the middle of the cell, what stage is occurring?

Metaphase.

What is the purpose of meiosis?

To produce haploid gametes.

What chromosome change occurs during meiosis?

$2N \rightarrow 1N$.

Which division is the reduction division?

Meiosis $I$.

Which division resembles mitosis?

Meiosis $II$.

During leptotene, chromosomes begin to condense. What nickname describes this stage?

Single-thread stage.

During zygotene, what structure forms?

Synaptonemal complex.

What does the synaptonemal complex do?

Aligns homologous chromosomes.

During pachytene, what major event occurs?

Crossing over.

During diplotene, what becomes visible?

Chiasmata.

What is a chiasma?

The visible site of crossover between homologous chromosomes.

What separates during Anaphase $I$?

Homologous chromosomes.

What separates during Anaphase $II$?

Sister chromatids.

What does true-breeding mean?

Individuals consistently produce offspring with the same trait when self-crossed.

What is the $P$ generation?

Parental generation.

What is the $F_1$ generation?

First filial generation.

What is the $F_2$ generation?

Second filial generation.

How do you determine which allele is dominant?

Observe which phenotype appears in the $F_1$ generation.

What is Mendel's Principle of Segregation?

Alleles separate during gamete formation.

What genotype ratio results from $Aa \times Aa$?

$1 AA : 2 Aa : 1 aa$.

What phenotype ratio results from $Aa \times Aa$ with complete dominance?

$3:1$.

What is a testcross?

Crossing an individual of unknown genotype with a homozygous recessive individual.

What result from a testcross indicates the unknown individual is heterozygous?

A $1:1$ phenotype ratio.

What is a sex-linked trait?

A trait determined by a gene located on a sex chromosome.

Most sex-linked traits studied in genetics are located on which chromosome?

The $X$ chromosome.

Why are males more likely to express $X$-linked recessive traits?

They possess only one $X$ chromosome.

What does hemizygous mean?

Having only one copy of a gene instead of two.

Why are males hemizygous for most $X$-linked genes?

Because they have only one $X$ chromosome.

Can a male be a carrier for an $X$-linked recessive trait?

No, he either has the trait or he does not.

Can a female be a carrier for an $X$-linked recessive trait?

Yes.

What genotype represents a carrier female for an $X$-linked recessive trait?

$X^AX^a$.

What genotype represents an affected male for an $X$-linked recessive trait?

$X^aY$.

What genotype represents an affected female for an $X$-linked recessive trait?

$X^aX^a$.

A carrier female ($X^AX^a$) mates with a normal male ($X^AY$). What fraction of sons are affected?

$50\%$.

A carrier female ($X^AX^a$) mates with a normal male ($X^AY$). What fraction of daughters are affected?

$0\%$.

A carrier female ($X^AX^a$) mates with a normal male ($X^AY$). What fraction of daughters are carriers?

$50\%$.

An affected male ($X^aY$) mates with a normal female ($X^AX^A$). What fraction of daughters are carriers?

$100\%$.

An affected male passes his $X$ chromosome to which offspring?

All daughters.

An affected male passes his $Y$ chromosome to which offspring?

All sons.

Why can fathers not pass $X$-linked traits directly to sons?

Sons receive the father's $Y$ chromosome.

What is a pedigree?

A diagram showing inheritance of traits through generations.

What symbol represents a male?

Square.

What symbol represents a female?

Circle.

What does a shaded symbol represent?

An affected individual.

What does an unshaded symbol represent?

An unaffected individual.

What does a horizontal line connecting two individuals represent?

Mating.

What does a vertical line represent?

Parent-offspring relationship.

What pattern is common in autosomal dominant traits?

Appears in every generation.

What pattern is common in autosomal recessive traits?

Can skip generations.

If two unaffected parents produce an affected child, what inheritance pattern is likely?

Autosomal recessive.

If every affected individual has an affected parent, what inheritance pattern is likely?

Autosomal dominant.

What is a hallmark of $X$-linked recessive inheritance?

More affected males than females.

What inheritance pattern often shows no father-to-son transmission?

$X$-linked inheritance.

What is a hallmark of mitochondrial inheritance?

Affected mothers transmit to all children.

Why don't affected fathers pass mitochondrial traits?

Mitochondria are inherited from the egg.

What does the product rule calculate?

Probability that independent events occur together.

What is the product rule formula?

Multiply the probabilities.

Probability of a male child?

$\frac{1}{2}$.

Probability of two sons in a row?

$\frac{1}{2} \times \frac{1}{2} = \frac{1}{4}$.

Probability of three daughters in a row?

$\frac{1}{8}$.

A trait has a $\frac{1}{4}$ chance of occurring. What is the probability of both being male and affected?

$\frac{1}{2} \times \frac{1}{4} = \frac{1}{8}$.

Why does the product rule work?

The events are independent.

When should probabilities be multiplied?

When ALL events must occur.