Exam 3 Flashcards

Vocabulary flashcards covering Mendelian genetics, meiotic processes, chromosomal inheritance, and the molecular mechanisms of DNA structure and replication.

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Autosomes

Any chromosome that is not a sex chromosome.

Alternation of generations

A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte.

Crossover

The exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis.

Fertilization

The process in which haploid gametes fuse to form a diploid zygote.

Gametophyte

The multicellular haploid stage in the life cycle of plants and algae that produces gametes.

Germ cells

Specialized cells within the gonads that undergo meiosis to produce gametes.

Meiosis

A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell.

Somatic cell

Any cell of a living organism other than the reproductive cells.

Spore

A haploid cell produced by the sporophyte that can grow into a new multicellular haploid organism (gametophyte) without fusing with another cell.

Sporophyte

The multicellular diploid stage in the life cycle of plants that produces haploid spores through meiosis.

Nondisjunction

An event during cell division where homologous chromosomes or sister chromatids fail to separate properly, resulting in gametes with abnormal chromosome numbers.

Trisomy 21 (Down Syndrome)

A condition caused by a nondisjunction event where an individual inherits three copies of chromosome $21$.

Haploid

A cell or nucleus containing a single set of unpaired chromosomes, represented as $n$.

Diploid

A cell or nucleus containing two complete sets of chromosomes, one from each parent, represented as $2n$.

Zygote

The diploid cell resulting from the fusion of a male and female gamete.

Homologous Chromosomes

Pairs of chromosomes in a diploid organism that have the same length, centromere position, and gene sequence, though they may have different alleles.

Continuous variation

A type of variation in traits that shows a range of phenotypes rather than discrete categories, such as human hair color or height.

Dominant

An allele or trait that is expressed in the phenotype even if only one copy is present (heterozygous state).

Heterozygous

Having two different alleles for a particular gene.

Homozygous

Having two identical alleles for a particular gene.

Incomplete dominance

A pattern of inheritance in which the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes.

Model system

A species that is widely studied, easy to maintain and breed in a laboratory setting, and used to understand particular biological phenomena.

Phenotype

The observable physical or biochemical characteristics of an organism, determined by its genotype and environment.

Punnett square

A diagram used to predict the genotypes and phenotypes of offspring resulting from a genetic cross.

Recessive

An allele or trait that is only expressed in the phenotype when two copies are present (homozygous state).

Sex-linked

Traits or genes located on the sex chromosomes (X or Y).

Test cross

The cross of an individual with an unknown dominant genotype with a homozygous recessive individual to determine the unknown genotype.

X-linked

A specific type of sex-linked trait where the gene is located on the X chromosome.

Centimorgan

A unit of measure for genetic linkage, defined as the distance between genes for which the recombination frequency is $1 \%$. Also known as a map unit.

Electrophoresis

A laboratory technique used to separate DNA fragments or proteins based on their size and charge using an electric field.

Helicase

An enzyme that untwists the double helix of DNA at the replication fork, separating the two strands.

Lagging strand

The DNA strand that is synthesized discontinuously in the $5'$ to $3'$ direction away from the replication fork, forming Okazaki fragments.

Leading strand

The DNA strand that is synthesized continuously in the $5'$ to $3'$ direction toward the replication fork.

Single-strand binding protein

Proteins that bind to the separated DNA strands during replication to prevent them from re-annealing.

Ligase

An enzyme that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.

Mutation

A permanent change in the DNA sequence of a genome.

Okazaki fragment

Short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication.

Point mutation

A mutation that affects a single nucleotide in the DNA sequence.

Primase

An enzyme that synthesizes a short RNA primer to initiate DNA synthesis by DNA polymerase.

Primer

A short stretch of RNA or DNA that provides the free $3'-OH$ group required for DNA polymerase to start synthesis.

Proofreading

A mechanism by which DNA polymerase identifies and corrects incorrectly incorporated nucleotides during replication.

Replication fork

The Y-shaped region of a DNA molecule where the two strands separate and new strands are synthesized.

Silent mutation

A mutation that changes a codon but does not result in a change in the amino acid sequence of the protein.

Telomerase

An enzyme that adds repetitive nucleotide sequences to the ends of eukaryotic chromosomes (telomeres) to prevent shortening during replication.

Telomere

The specialized structure at the end of a eukaryotic chromosome that contains repetitive non-coding sequences.

Topoisomerase

An enzyme that prevents the over-winding (supercoiling) of the DNA double helix ahead of the replication fork.

Transformation

The process by which a cell takes up foreign DNA from its environment and incorporates it into its own genome.

Sanger sequencing

A method of DNA sequencing based on the selective incorporation of chain-terminating dideoxynucleotides by DNA polymerase during in vitro DNA replication.

Explain why sexual reproduction is beneficial to a population but can be detrimental to an individual offspring.

Sexual reproduction increases genetic diversity within a population, enhancing adaptability to changing environments. However, it can be detrimental to individual offspring due to the higher likelihood of inheriting deleterious alleles or being less fit in specific environmental contexts.

List and briefly describe the three processes that lead to variation in offspring with the same parents.

The three processes are: 1) Crossing over - the exchange of genetic material between homologous chromosomes during meiosis. 2) Independent assortment - the random distribution of maternal and paternal chromosomes into gametes. 3) Random fertilization - the unpredictability of which sperm will fertilize which egg, creating unique genetic combinations.

How do organisms with haploid-dominant life cycles ensure continued genetic diversification in offspring without using a meiotic process to make gametes?

random fertilization of different mating types and post-fertilization recombination

Why is it more efficient to perform a test cross with a homozygous recessive donor than a homozygous dominant donor? How could the same information still be found with a

homozygous dominant donor? Illustrate with punnet squares.

Gotta work this out for yourself

Are all traits mendelian? If not, what are some traits in humans that don't follow the pattern.

Not all traits are mendelian, some traits in humans exhibit complex inheritance patterns, such as polygenic traits (like height and skin color) and traits influenced by environmental factors (like susceptibility to certain diseases).

Draw an autosomal recessive pedigree for 3 generations, include genotypes. You must include homozygous dominant, homozygous recessive, and heterozygous genotypes.

I would recommend practice

Can a human male be a carrier of red-green color blindness?

No because males are hemizygous for x chromosome, meaning they have only one X chromosome. A single recessive allele on the X chromosome will express the trait.

Be able to draw out Meisosis I and Meisosis II, how do the daughter cells inherit chromosomes. Draw non-disjunction events in meiosis 1 vs 2. Annotate the ploidy of the daughter cells.

The circle diagram with 4n etc in it.

Describe how two genes can be linked together, what process can split them apart.

Two genes are linked if they are close together on the chromosome. They can be separated by crossing over.

How does knowing what chromosomes are affect the modern understanding of genetics?

Knowing that chromosomes are DNA tightly wound around proteins allows us to study both the base pairs of the DNA as well as things like DNA methylation and histone modifications

What are Okazaki fragments and how are they formed?

Okazaki fragments are short segments of DNA synthesized on the lagging strand during DNA replication. They are formed discontinuously as RNA primers are laid down, allowing for DNA polymerase to synthesize the new strand in a 5' to 3' direction.

Describe the structure and complementary base pairing of DNA.

The structure of DNA is a double helix formed by two strands of nucleotides, which are composed of a sugar, phosphate group, and a nitrogenous base. Complementary base pairing occurs when adenine pairs with thymine, and cytosine pairs with guanine, held together by hydrogen bonds.

Provide a brief summary of the Sanger sequencing method.

The Sanger sequencing method, also known as chain termination sequencing, is a technique used to determine the nucleotide sequence of DNA. It involves using labeled dideoxynucleotides to terminate DNA strand elongation, allowing for the selective amplification and subsequent identification of specific DNA fragments.

What is the role of a primer in DNA replication? What would happen if you forgot to add a primer in a tube containing the reaction mix for a DNA sequencing reaction

A primer in DNA replication serves as a short segment of RNA or DNA that provides a starting point for DNA synthesis. If a primer is not added, DNA polymerase cannot initiate the synthesis of new DNA strands, preventing replication from occurring.

What is the consequence of mutation of a mismatch repair enzyme? How will this affect the function of a gene?

A mutation in a mismatch repair enzyme can lead to an inability to correct base-pairing errors during DNA replication. This can result in an accumulation of mutations in the gene, potentially disrupting its normal function and leading to conditions such as cancer.

How do the linear chromosomes in eukaryotes ensure that its ends are replicated completely?

Eukaryotic linear chromosomes have specialized structures called telomeres at their ends, which protect the chromosome from degradation and prevent the loss of essential genetic information during replication. The enzyme telomerase extends the telomeres, ensuring complete replication and maintenance of chromosome stability. Telomerase essentially exhibits a copy and paste functionality to the end of the chromosome.