Exam 1 (final)

What is reproduction?

The process by which new cells or organisms are produced.

What must daughter cells receive during reproduction?

The correct set of chromosomes.

What is sexual reproduction?

Two individuals combine genetic information to make offspring.

What is asexual reproduction?

One parent produces genetically identical offspring.

Which organisms commonly use asexual reproduction?

Prokaryotes

Which organisms commonly use sexual reproduction?

Eukaryotes

How do bacteria reproduce?

By binary fission.

Where is prokaryotic DNA found?

In the nucleoid, in a circular chromosome

What does “diploid (2n)” mean?

Two sets of chromosomes—one from each parent

Human diploid number?

46 chromosomes (2n = 46)

Human haploid number?

23 chromosomes (n = 23).

What are homologous chromosomes?

Chromosome pairs containing the same genes in the same locations.

What are sister chromatids?

Identical copies of a chromosome after replication, joined at the centromere

What is a locus?

The physical location of a gene on a chromosome.

What are alleles?

Different versions of the same gen

Are X and Y chromosomes homologous?

No—only short regions are homologous

Why does meiosis occur?

To create haploid gametes for sexual reproduction.

What types of cells are somatic cells?

Diploid

What types of cells are gametes?

Haploid

What are the two parts of mitosis?

Karyokinesis (nuclear division) and cytokinesis (cytoplasm division).

Major cell cycle checkpoints?

G1, G2, and M.

Purpose of mitosis?

To create two genetically identical daughter cells.

What happens in prophase?

Chromosomes condense, nuclear envelope breaks down, spindle forms.

What happens in metaphase?

Chromosomes align at the equatorial plate.

What happens in anaphase?

Sister chromatids separate to opposite poles.

What happens in telophase?

Chromosomes decondense and nuclei reform.

What follows mitosis?

Cytokinesis

What is the purpose of meiosis?

To produce four genetically distinct haploid gametes

Main event of Meiosis I?

Homologous chromosomes separate.

Is Meiosis I diploid → haploid?

Yes (reduction division).

What separates in Meiosis II?

Sister chromatids

Does DNA replicate before Meiosis II?

No

What is crossing over?

Exchange of DNA between homologous chromosomes during Prophase I.

What is a chiasma?

Visible site where crossing over occurs.

What explains Mendel’s Law of Segregation?

Separation of homologous chromosomes in Meiosis I.

What explains Mendel’s Law of Independent Assortment?

Random alignment of homologous chromosomes during Meiosis I.

How many gametes result from spermatogenesis?

Four equal sperm cells.

What do plants produce by meiosis?

Spores

How are plant gametes made?

Through mitosis in the gametophyte stage.

What does DNA contain?

The genetic blueprint needed to survive, reproduce, and respond to the environment.

What is a gene?

A region of DNA that can be transcribed into RNA

What usually happens to RNA?

It is translated into a protein.

What is the genome?

All the DNA in an organism.

How many chromosome sets do diploid organisms have?

Two—one from each parent.

What are homologous chromosomes?

Chromosomes with the same genes in the same order, but possibly different alleles.

Why were pea plants a good study organism?

They grow quickly, mate easily, and produce many offspring.

What is genetics?

The study of heritable traits.

What is a trait?

A variation of a physical characteristic (e.g., flower color).

What does “true-breeding” mean?

Produces identical offspring when self-fertilized

What is a monohybrid cross?

A cross between two individuals that differ in ONE trait.

What did Mendel notice about traits in F1?

Dominant traits appear; recessive traits disappear.

Postulate 1?

Each organism has two alleles for a trait.

Postulate 2?

Alleles can be homozygous or heterozygous; dominant masks recessive

Postulate 3 (Law of Segregation)?

Alleles separate during gamete formation; each gamete gets one allele.

Define phenotype.

Outward physical appearance

Define genotype.

enetic makeup (alleles present).

Which allele is expressed in a heterozygote?

Dominant

What is a test cross?

Crossing an organism with unknown dominant genotype to a homozygous recessive.

Why perform a test cross?

To determine if the dominant organism is homozygous or heterozygous.

What is a dihybrid cross?

A cross involving two traits.

What does Mendel’s Law of Independent Assortment state?

Alleles of different genes separate independently during meiosis.

Phenotypic ratio for a classic dihybrid cross

9:3:3:1

Product rule?

Probability of two independent events = multiply their probabilities.

Sum rule?

Probability of A OR B = sum of their probabilities.

What is the forked-line method used for?

Predicting outcomes for crosses involving 2+ genes without huge Punnett squares.

What does chi-square analysis test?

Whether observed genetic data match expected ratios.

Why do we use chi-square?

To see if deviations are due to chance.

What is a pedigree?

A family tree showing inheritance of a trait.

What is sex determination?

The mechanism by which an individual develops into an egg-producer (female) or sperm-producer (male).

What is the difference between autosomes and sex chromosomes?

Autosomes do not determine sex; sex chromosomes (X and Y) do.

What is the chromosomal makeup of human males and females?

Males = XY (heterogametic), Females = XX (homogametic)

What gene determines male development in humans?

The SRY gene on the Y chromosome.

Which chromosome contains more genes: X or Y?

X chromosome

What are PARs?

Pseudoautosomal regions where X and Y chromosomes pair during meiosis.

hat does hemizygous mean?

Having only one allele for a gene

How do X-linked inheritance patterns differ from autosomal patterns?

Males have only one X allele; traits express immediately if recessive

What is a reciprocal cross?

Two crosses differing in which parent carries the trait; differences indicate sex-linkage.

X-linked recessive traits

Rare in females
• Carrier females → 50% affected sons
• May skip generations

X-linked dominant traits

Appears every generation
• Affected males → all daughters affected, no affected sons

What is dosage compensation?

Equalizing X-linked gene expression between XX and XY individuals.

What is a Barr body?

An inactivated X chromosome in females

What does X-inactivation create in females?

A mosaic pattern (e.g., calico cats

What gene drives X-inactivation?

Xist, located in the X-inactivation center (Xic), expressed only on the inactivated X.

In pedigree analysis, what suggests an X-linked recessive trait?

Mostly males affected; unaffected mothers transmit to sons.

In pedigree analysis, what suggests an X-linked dominant trait?

Affected fathers → all daughters affected; no affected sons.

What is a mutant allele?

A version of a gene that differs from wild-type, often due to mutation

What is a loss-of-function allele?

A mutant allele that produces little or no functional protein; usually recessive.

Why do most mutant alleles behave recessively?

Because one wild-type allele is usually enough to provide normal function.

What is a gain-of-function mutation?

A mutation causing increased, new, or abnormal protein activity; often dominant.

What is haploinsufficiency?

When one wild-type allele is not enough for normal function → mutant phenotype is dominant.

What is incomplete dominance?

Heterozygote shows an intermediate phenotype between the two homozygotes.

What phenotypic ratio occurs with incomplete dominance?

1:2:1 phenotype ratio

What is codominance?

Both alleles in a heterozygote are fully and equally expressed

Which common human trait shows codominance?

ABO blood type

What does “multiple alleles” mean?

More than two alleles exist for a gene in the population

What is a recessive lethal allele?

Homozygous recessive individuals die; observed ratio becomes 2:1 instead of 3:1.

What is a dominant lethal allele?

A single copy causes death

What inheritance pattern is seen in Manx cats?

A dominant allele is lethal in homozygotes → 2:1 ratio of live kittens.

What is gene interaction?

When two or more genes influence a single trait.

What is epistasis?

When one gene masks or modifies the expression of another gene