Genetics Exam 1

What is DNA?

The genetic material of a cell.

What is gene expression?

DNA is transcribed into RNA, which is then translated into a polypeptide composed of amino acids.

What are sources of genetic variability?

Variations in gene sequence or gene expression (usually caused by variation in noncoding DNA) cause trait variation. Mutation in genes, and variation in chromosome number or structure can cause genetic variability.

What is meant by: Transmission genetics?

The study of the traits that are passed from parent to offspring.

What is meant by: Molecular genetics?

The study of the differences in the structures or expression of DNA molecules that result in variation among organisms.

What is meant by: Population and Evolutionary genetics?

The study of allelic frequency in a population and how it evolves (changes) with time.

Understand what is meant by P generation, F1 generation, F2 generation, etc.

The P generation are two true-breeding strains of a single gene that are crossed to produce an F1 generation. The F1 generation is the offspring of the P generation and usually only shows the dominant genotype, but is heterozygous. The F2 generation is the offspring of the F1 generation and shows a 3:1 ratio of dominant to recessive traits.

What is an allele?

Different versions of genes

What does it mean for an allele to be dominant? Recessive?

A dominant allele is a variation of a gene that will produce a certain phenotype, even in the presence of other alleles. A dominant allele typically encodes for a functioning protein. A recessive allele is a variety of genetic code that does not create a phenotype if a dominant allele is present. A recessive allele typically encodes for a non-functioning protein.

What is the molecular basis for dominance?

Having at least one dominant allele produces enough of the product (most likely an enzyme) to express the trait.

What is a homozygote?

An individual with two same versions of an allele.

What is a heterozygote?

An individual with two different versions of an allele.

What is a phenotype? A genotype?

A phenotype is a physical trait. A genotype is the underlying genetic makeup responsible for the trait. CANNOT OBSERVE GENOTYPE

What is Mendel's Law of Segregation?

The two copies of a gene segregate (or separate) from each other during transmission from parent to offspring.

What is Mendel's Law of Independent assortment?

Two different genes will randomly assort their alleles during the formation of haploid cells.

Sum Rule

The probability that one of two or more mutually exclusive events will occur is the sum of their respective probabilities. "OR"

Product Rule

The probability that two or more independent events will occur is equal to the product of their respective probabilities. "AND"

Binomial expansion equation

Represents all of the possibilities for a given set of unordered events.

What are homologous chromosomes?

The singular of each pair of chromosomes, same genes, different alleles.

Describe the phases of the cell cycle.

Interphase (G1, S, and G2) and Mitosis (Prophase, Prometaphase, Metaphase, Anaphase, Telophase, and Cytokinesis)

Describe the phases of mitosis.

Prophase (Chromosomes condense, nuclear envelope dissociates, centromeres migrate to poles), Prometaphase (sister chromatids interact with spindle fibers, kinetochore microtubules capture sister chromatids), Metaphase (sister chromatids are aligned along the metaphase plate), Anaphase (sister chromatids are separated, kinetochore microtubules shorted, polar microtubules lengthen, each chromatid is now a chromosome), and Telophase (Chromosomes relax, nuclear envelope reforms, cytokinesis results in cell division)

What are the products of mitosis and cytokinesis?

Two genetically identical daughter cells with the same chromosome number.

Describe the phases of meiosis

Meiosis begins after interphase but consists of two rounds of cell division, meiosis 1 and 2.

Prophase 1 can be further divided into

Leptotena (replicated chromosomes condense), Zygotena (bivalent forming, synapsis begins), Pachytena (crossing over occurs), Diplotena (Synaptonemal complex dissociates), and Diakinesis (nuclear membrane fragmenting)

What are the products of meiosis?

4 haploid daughter cells, each with half the chromosome number as the parent.

What is a bivalent?

One pair of chromosomes in a tetrad.

What is crossing over? Why is it important?

Crossing over is a physical exchange of chromosome pieces. It generates genetic variability of offspring.

What is independent assortment? Why is it important?

The variation of tetrads on the metaphase plate. Can result in a variability of haploid products.

How are Anaphase I and independent assortment related to Mendel's Law of Independent assortment?

The tetrads are separated independently and can happen in a variety of ways, making them have independent assortment.

What are some differences between Oogenesis and Spermatogenesis?

In spermatogenesis, 4 haploid spermatids result compared to oogenesis and the result of 1 haploid egg cell. In oogenesis, the divisions are asymmetric and in spermatogenesis, they are symmetrical.

What is "alternation of generations" in plants?

Generations alternate from haploid to diploid.

How is gender determined genetically?

The male's sperm, which could have the X or Y chromosome. A female's contribution can only be X.

What is an X-linked trait? How is their inheritance pattern different from an autosomal trait?

A trait that is only linked to the X chromosome. Males only have one X chromosome, so if their x chromosome is affected, they do not have another working X chromosome to "cover" the nonfunctional X.

Describe the molecular basis for dominance.

A dominant trait codes for a functional protein. Recessive means non-functional.

Describe incomplete dominance? What is its molecular basis?

When only 50% of the trait is functional (ex. red and white 4-o'clocks producing a pink flower). Only 50 percent of the functional protein is there to create the pigment, protein, etc.

Describe incomplete penetrance. What might be happening on the molecular level? How does one calculate penetrance?

Incomplete penetrance is when an individual has a dominant allele molecularly, but does not show it phenotypically. Penetrance is calculated by how many heterozygotes show the trait.

How do genotype and environment interact to determine phenotype?

Phenotypic plasticity, meaning an individuals response to a unique environment. Genes determine traits, but also interact with the environment the individual is in.

What is overdominance? Describe some different molecular mechanisms to explain overdominance.

Overdominance is when the heterozygote has an advantage homozygotes do not achieve (most fit). With sickle cell disease, the heterozygote has enough normal blood cells to be unaffected by the disease, but also are malaria resistant.

What is codominace? Be able to track the inheritance of codominant alleles.

Blood type-A and B are both co-dominant to O, and can be dominant with one another (blood type AB).

What is pseudoautosomal inheritance?

A trait that looks autosomal, but is sex-linked due to the same alleles on the X and Y chromosomes (ex. Mic2 gene).

What is sex-influenced inheritance? What is its molecular basis?

Hormone influenced traits, mainly interacts with testosterone. An allele is dominant in one sex, but recessive in the other. Ex. Male pattern baldness in humans (D in males, R in females).

How might lethal alleles affect phenotype ratios resulting from crosses?

The individuals that have the lethal alleles are not accounted for because they die before being counted.

What is pleiotrophy? What is its molecular basis?

Pleiotrophy describes the condition of one gene having many effects. Ex. Cystic Fibrosis impacts the chloride channels of the body, which then impacts the lungs.

What is epistasis? Complementation? Be able to work epistasis crosses.

Epistasis is an inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene (Looks like dihybrid, but is monohybrid with 2 genes contributing to 1 trait. Ex. comb types, 9:7). Complementation is a phenomenon in which two different parents that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype (Two white flowers, CCpp x ccPP, can produce purple flowers, CcPp, because having at least 1 dominant C and P produce the wild-type).

Be able to determine outcomes of crosses involving the following: Gene modifiers, Gene redundancy, Intergenic suppressors.

Gene modification is a phenomenon in which the allele of one gene modifies the phenotypic outcome of the alleles of a different gene (coat color in rodents, if cc - A is irrelevant, if aa - C is irrelevant). Gene redundancy is a pattern in which the loss of function in a single gene has no phenotypic effect, but the loss of function of two genes has an effect (knockout effect in paralogs). Intergenic suppressors is an inheritance pattern in which the phenotypic effects of one mutation are reversed by a suppressor mutation in another gene (Ex. hairless-suppressor of hairless heterodimer).

What is linkage? Why does it occur?

Linkage is the phenomenon when genes that are found on the same chromosome violate Mendel's law of independent assortment. Genes that are found close together on the same unit are linked and tend to be transmitted as a unit.

What is a recombinant? A nonrecombinant?

Recombinant (parental) are the products of crossing over that result in the same alleles segregating together, resulting in the same makeup as the parent cells. Nonrecombinant (nonparentals) result from the crossing over and reassortment during meiosis, and the products do not look like the parent cells.

What is the relationship between recombination and crossing-over?

If there is no crossing over present, parental offspring will result.

What is a testcross?

A genetic cross between a homozygous recessive individual and a corresponding suspected heterozygote to determine the genotype of the offspring.

What is the relationship between map distance and crossing-over?

The physical distance of the genes from one another on the chromosome (in map units) is related to the frequency of crossing-over between them.

Why is the calculation of map distance using testcrosses more accurate for genes that are closer together? How does one overcome this problem for genes that are further apart?

With closer genes, we can be more accurate due to the fact that very few recombinant offspring will result, meaning fewer double crossovers would be possible. Taking into account double crossovers overcomes the underestimation. (SCOI + SCOII + 2(DCO) / total x 100)

What is interference? Be able to calculate values for positive interference.

Interference is calculated by finding the probability of a double crossover by the product rule, and then comparing it to the observed. A lower-than-expected value is due to a common genetic phenomenon, termed positive interference. I = 1 - C, where C is the coefficient of coincidence (Obs/exp)

How are maternal effect genes inherited? What is the molecular basis for this?

The mother's genotype determines the offspring's phenotype (delayed by one generation) due to the gene products that the mother provides to her egg.

What is epigenetic inheritance?

When a nuclear gene or chromosome is modified, thus affecting gene expression. A way for an individual to respond to the environment. Ex. ladybug armoring shell.

What is X-inactivation? Why must is occur?

A way of dosage compensation that offsets differences in the number of sex chromosomes between genders. A compacted X chromosome, known as a Barr body, can prevent unwanted information to be passed down.

What are some of the interesting phenotypic ramifications of X inactivation?

Patches of black and white fur on a mouse due to random X chromosome inactivation.

What is the molecular basis for x-inactivation?

X Inactivation Depends on Xic, Xist, TsiX and Xce. Xist RNA promotes compaction while Tsix RNA prevents compaction. Tsix prevents Xist on the other chromosome, you can only have one or the other.

What is genomic imprinting? What is its molecular basis Be able to predict the outcome of crosses involving imprinted genes.

Either the maternal or paternal allele is expressed in the offspring, but not both. In mice, the Igf-2 gene (Insulin-like growth factor) is necessary for normal size. The paternal allele is transcribed. The maternal is not.

What is DNA Methylation?

The ability to silence genes by using transcription factors binding sites that promote or inhibit genes being read. If the sequence is methylated, the gene is usually not expressed because transcription is prevented.

What is extranuclear inheritance?

Inheritance that involves genes from outside the nucleus. This can include mitochondria (semi-autonomous) or plastids (prokaryotes, bacteria).

What is the endosymbiotic theory?

This theory states that mitochondria originated from gram-negative nonsulfur purple bacteria and chloroplasts originate from cyanobacteria.

What are some of the problems that may occur with chromosome structure? When do these problems arise?

What is polyploidy? Why is it sometimes important in plants?

Polyploidy is when an entire extra set of chromosomes are present (triploid, tetraploid). If a copy is broken in a plant, it can be okay because multiple copies are available.

What is aneuploidy?

Aneuploidy is when there is an addition or subtraction of only one chromosome (Trisomy, monosomy)

What is nondisjunction?

Nondisjunction is when chromosomes do not split in either meiosis 1 or 2.

A first division segregation (FDS) has what arrangement?

4:4, anything else is SDS