Inheritance and Genes

Why do homologous chromosomes in a sexually reproducing organism carry different alleles?

Because the chromosomes are inherited from two genetically different parents, with unique mutations accumulated in their separate lines of descent.

New alleles arise through what process?

Mutation.

In sexual reproduction, what percentage of each parent's genes are passed to the offspring?

50% from each parent.

What is the primary evolutionary advantage of sexual reproduction over asexual reproduction, especially in changing environments?

It creates high genetic diversity among offspring.

Offspring of asexual reproducers are _____, meaning they are genetically identical to their parent in the absence of new mutations.

clones

What is the name of the nuclear division mechanism that halves the chromosome number and is essential for forming haploid cells?

Meiosis

What term describes a cell, such as an egg or sperm, that has one copy of each chromosome (n)?

Haploid

During which specific phase of meiosis I do homologous chromosomes align tightly and swap segments?

Prophase 1

The process by which a chromosome and its homologous partner exchange corresponding pieces of DNA during meiosis is known as _____.

crossing over

What is the result of crossing over?

It introduces novel combinations of alleles on the chromosomes that end up in offspring.

During which phase of meiosis do homologous chromosomes separate and move toward opposite spindle poles?

Anaphase I.

At the end of Meiosis I, the two new nuclei are described as what ploidy level?

Haploid (n).

During which phase of meiosis do sister chromatids separate?

Anaphase II.

Meiosis in one diploid (2n) cell produces how many haploid (n) cells?

4

What is the fusion of two haploid gametes called, and what diploid cell does it produce?

It is called fertilization, and it produces a zygote.

In animals, meiosis in diploid germ cells gives rise to female gametes, called _____, and male gametes, called _____.

eggs; sperm

If meiosis did not precede fertilization, what would happen to the chromosome number with every generation?

The chromosome number would double.

With _____, a single individual produces offspring that are genetically identical to their parent.

asexual reproduction

What type of asexual reproduction involves a new individual developing as an outgrowth from an existing one, as seen in hydras?

Budding.

What is parthenogenesis?

A form of asexual reproduction where a new individual develops from an unfertilized egg.

What term describes a sexually reproducing individual that can make both eggs and sperm?

Hermaphrodite.

In _____, gametes are released into the water where fertilization occurs, a process common in most aquatic invertebrates and bony fishes.

external fertilization

What is the thick, nutrient-rich fluid deposited in an egg to nourish a developing animal?

Yolk.

How do placental mammals, including humans, nourish their embryos instead of using yolk?

By means of a placenta, which facilitates substance exchange between maternal and embryonic bloodstreams.

During early animal development, the process of _____ involves mitotic cell divisions that increase the cell number without increasing the zygote's original volume.

cleavage

Cleavage ends with the formation of a _____, which is a hollow ball of cells with a fluid-filled center.

blastula

What is the developmental process where a blastula undergoes structural rearrangement to form a three-layered gastrula?

Gastrulation.

What are the three primary tissue layers of a gastrula?

Ectoderm (outer), mesoderm (middle), and endoderm (inner)

From which primary tissue layer do the epidermis and nervous tissue develop?

Ectoderm.

From which primary tissue layer do muscles, blood vessels, and most bones develop?

Mesoderm.

What is a larva, as seen in the life cycle of a frog?

An immature animal that differs in form from the adult.

In humans, where do sperm form?

Inside the male gonads, called testes.

What are the primary female sex hormones secreted by the ovaries?

Estrogens and progesterone.

What is the function of the oviduct (fallopian tube) in the female reproductive system?

It connects the ovary to the uterus and is the site where an egg is usually fertilized.

The uterine lining, which consists of glandular epithelium, connective tissues, and blood vessels, is called the _____.

endometrium

What is an oocyte?

An immature egg.

In the ovarian cycle, what event is triggered by a mid-cycle surge of Luteinizing Hormone (LH)?

Ovulation.

After ovulation, the ruptured follicle cells develop into a hormone-secreting structure called the _____.

corpus luteum

What is the primary function of the hormones estrogen and progesterone secreted by the corpus luteum?

To cause the uterine lining to thicken and grow more blood vessels in preparation for pregnancy.

What process begins the menstrual cycle if pregnancy does not occur?

Menstruation, the shedding of the uterine lining.

What is the function of the scrotum in the male reproductive system?

It holds the testes and adjusts their position to maintain a temperature optimal for sperm production.

In what coiled duct do sperm mature and become motile after forming in the testes?

The epididymis.

What is semen?

A thick, white fluid containing sperm and secretions from accessory glands like the seminal vesicles and prostate gland.

The _____ gland secretes a fructose-rich fluid that sperm use as an energy source.

seminal vesicle

Where does sperm production occur within the testes?

In coiled, sperm-making seminiferous tubules.

What is the function of the enzyme-containing cap on the head of a mature sperm?

It helps the sperm penetrate the egg during fertilization.

In _____, one allele is not fully dominant over the other, so the heterozygous phenotype is an intermediate blend.

incomplete dominance

What is the inheritance pattern where traits associated with two alleles are fully and equally apparent in heterozygous individuals, such as in ABO blood types?

Codominance.

In the ABO blood group system, which allele(s) are codominant, and which is recessive?

Alleles A and B are codominant; allele O is recessive.

A person with which ABO blood type is considered a universal donor?

Type O.

What is pleiotropy?

An inheritance pattern where a single gene influences multiple traits.

Marfan syndrome, which affects elastic tissues in the heart, skin, and blood vessels, is caused by mutations in the gene for what protein?

Fibrillin.

In _____, alleles of two or more genes collectively affect a single trait, such as human skin color.

polygenic inheritance

How can environmental factors affect an organism's phenotype?

By influencing the expression of genes.

What is the term for a permanent change in the DNA sequence of a chromosome?

Mutation.

A _____ is a mutation where one base pair is changed to another.

base-pair substitution

Sickle-cell anemia results from a base-pair substitution in the gene for what protein?

v\Beta globin, a component of hemoglobin.

What type of mutation, involving the loss or addition of nucleotides, often causes a frameshift in the mRNA reading frame?

Deletion or insertion.

What are proteins that affect whether and how fast a gene is transcribed by binding to regulatory sites in DNA?

Transcription factors.

In embryonic development, _____ are genes whose expression begins a cascade that results in the formation of specific body parts.

master regulators (or homeotic genes)

What is X chromosome inactivation?

A process in female mammals where one of the two X chromosomes in each cell is condensed and transcriptionally silenced, forming a Barr body.

Potentially heritable modifications to DNA that affect gene expression without changing the DNA sequence are said to be _____.

epigenetic

What is the central flow of information during gene expression, often called the central dogma?

from DNA to RNA to protein

The process of copying a gene into RNA form is called _____.

transcription

What are the four nucleotide bases found in RNA?

Adenine (A), guanine (G), cytosine (C), and uracil (U).

What is the function of messenger RNA (mRNA)?

It carries a protein-building message from the DNA to the ribosome for translation.

What is the function of transfer RNA (tRNA)

It delivers amino acids to ribosomes in the order specified by an mRNA.

What enzyme carries out transcription?

RNA polymerase.

In eukaryotic genes, what are the non-coding regions that are removed from a newly transcribed RNA called?

Introns.

What is alternative splicing?

A process where exons of a gene are rearranged and spliced together in different combinations, allowing one gene to encode multiple versions of a protein.

The protein-building information in an mRNA is encoded in three-nucleotide units called _____.

codons

What is the typical 'start' codon in an mRNA, and what amino acid does it specify?

AUG, which specifies methionine.

What is an anticodon?

A triplet of nucleotides on a tRNA molecule that base-pairs with a specific mRNA codon.

What cellular organelle, composed of rRNA and proteins, is responsible for protein synthesis?

Ribosome

In what part of the cell does translation occur?

cytoplasm

Translation ends when the ribosome reaches a _____ in the mRNA.

stop codon

What is a one-nucleotide DNA sequence variation carried by a measurable percentage of a population called?

A single-nucleotide polymorphism (SNP).

What enzymes are used to cut DNA at specific nucleotide sequences, enabling the creation of recombinant DNA?

Restriction enzymes.

What is recombinant DNA?

A hybrid molecule consisting of genetic material from two or more organisms, created by joining DNA fragments.

What is the purpose of the polymerase chain reaction (PCR)?

To mass-produce (amplify) copies of a particular section of DNA.

What is the name of the heat-tolerant DNA polymerase used in PCR, isolated from bacteria living in hot springs?

Taq polymerase.

What technique uses an electric field to separate DNA fragments by length through a semisolid gel?

Electrophoresis.

What is DNA profiling?

The process of identifying an individual by their unique DNA patterns, such as SNPs or short tandem repeats.

Regions of DNA where a series of two to six nucleotides is repeated many times in a row are called _____.

short tandem repeats (or microsatellites)

What is a genetically modified organism (GMO)?

An organism whose genome has been deliberately engineered to modify its phenotype.

A _____ organism is a GMO that carries a gene from a different species.

transgenic

What is gene therapy?

The transfer of a gene into an individual's body cells with the intent to correct a genetic disorder or treat a disease.

What is CRISPR-Cas9?

A gene editing system where an enzyme (Cas9) is guided by an RNA molecule to cut a specific DNA sequence in a living cell.

What is a pedigree in the context of human genetics?

A chart that marks the appearance of a trait among generations of family members.

What is the difference between a genetic disorder and a genetic abnormality?

A genetic disorder causes medical problems, while a genetic abnormality is a rare but harmless version of a trait.

A trait associated with a dominant allele on an autosome (an _____ trait) appears in every generation of a family.

autosomal dominant

Individuals who are heterozygous for an autosomal recessive trait are called _____, because they have the allele but not the trait.

carriers

Why do X-linked recessive disorders appear more often in males than in females?

A male has only one X chromosome, so he only needs to inherit one recessive allele to be affected, whereas a female must inherit two.

What is aneuploidy?

A condition of having too many or too few copies of a particular chromosome.

What is the most common cause of aneuploidy?

Nondisjunction, the failure of chromosomes to separate properly during meiosis.

Down syndrome is caused by an aneuploid condition called _____, where an individual has three copies of chromosome 21.

trisomy 21

What is the chromosomal makeup of an individual with Turner syndrome?

One X chromosome and no corresponding X or Y chromosome (XO).

What is the chromosomal makeup of an individual with Klinefelter syndrome?

Two or more X chromosomes in a male (e.g., XXY).

What is the purpose of prenatal diagnosis?

To check a fetus for physical abnormalities and genetic disorders before birth.