Final Exam Flashcards
(54 cards)
Mendel’s Law of Segregation
Mendel’s Law of Segregation states that during the formation of gametes (sperm and egg cells), the two alleles for a given trait separate, so that each gamete carries only one allele for that trait. This means that each parent contributes only one of their two copies of a gene to their offspring.
Mendel’s Law of Independent Assortment
Mendel’s Law of Independent Assortment states that the inheritance of one trait does not influence the inheritance of another trait. In simpler terms, this means that different genes and their corresponding alleles (variants of a gene) separate independently of one another during the formation of gametes (sex cells).
Recombinant Mapping
The # of recombinant offspring / total # of offspring x 100% = recombination frequency
Recombination frequency = map units = centiMorgan (cM).
Aneuploidy
a condition where a cell or organism has an abnormal number of chromosomes. This can be due to having extra chromosomes (trisomy) or missing chromosomes (monosomy). A normal human cell has 46 chromosomes
Crossing over
outcome
a crucial process in genetics where homologous chromosomes exchange genetic material during meiosis, leading to increased genetic variation in offspring
1 normal, one duplicated, one inversion and one deletion
Cytosine deamination into uracil and permanent mutation
can lead to permanent mutations because uracil, which has a different base-pairing behavior than cytosine, can be incorporated into DNA during replication, resulting in a C:G to T:A transition
This occurs when uracil, formed from the deaminated cytosine, pairs with adenine instead of guanine during DNA replication, leading to a change in the original DNA sequence.
Double stranded break and issue repairing
Double-stranded breaks are breaks where both strands of a DNA molecule are damaged.
This pathway uses a homologous DNA sequence (like a sister chromatid) as a template to repair the broken DNA strand. It’s considered the most accurate repair method.
This pathway rejoins the broken DNA ends directly, without needing a homologous template. It’s often used when HR is not available, but it can introduce small insertions or deletions at the repair site.
Base Excision Repair (BER)
- Base Removal:
A DNA glycosylase enzyme recognizes and removes the damaged or incorrect base, creating an apurinic/apyrimidinic (AP) site. - AP Site Processing:
An AP endonuclease cleaves the sugar-phosphate backbone at the AP site, creating a single-strand break. - Gap Filling and Ligation:
DNA polymerase (Pol β) fills the gap with the correct nucleotide, and DNA ligase seals the nick, restoring the original DNA sequence.
One repair mechanism for DBS
This pathway uses an undamaged sister chromatid or homologous chromosome as a template to repair the break. This ensures a precise repair without introducing mutations. HR is initiated by the recognition of the DSB by proteins like the MRN complex (Mre11, Rad50, and Nbs1), which then facilitates the use of the homologous template for repair.
Compare genetic outcomes of meiosis and mitosis
Mitosis produces two genetically identical daughter cells from a single parent cell, while meiosis results in four genetically unique daughter cells, each with half the number of chromosomes of the parent.
Incomplete dominance
a heterozygous individual’s phenotype is a blend of the two homozygous phenotypes, rather than one being completely dominant over the other. This results in an intermediate trait where both alleles are expressed to some degree.
Codominance
In codominance, both alleles for a trait are expressed equally in a heterozygote, meaning the offspring exhibits both traits.
(EG: AB blood type)
Degrees of dominance
refers to how one allele’s expression masks or influences the expression of another allele in a heterozygote.
This can range from complete dominance, where the dominant allele completely hides the recessive allele, to incomplete dominance, where the heterozygote shows a blended phenotype, and co-dominance, where both alleles are expressed simultaneously.
Dihybrid cross
a breeding experiment where two organisms, each heterozygous for two traits, are crossed. This results in a characteristic 9:3:3:1
Epistasis in regards to dihybrid cross and genes
a type of gene interaction where one gene’s allele masks or modifies the phenotypic expression of another gene at a different locus.
This interaction can alter the expected phenotypic ratios in a dihybrid cross, which typically predicts a 9:3:3:1 ratio when two genes are independently segregating.
sex-limited
a characteristic that is expressed in only one sex of a species, even though both males and females carry the gene for that trait
sex-influenced
a genetic trait where the expression of a gene differs between males and females, despite the gene not being on the sex chromosomes
X-linked inheritance
the passing down of genetic traits or disorders located on the X chromosome
In X-linked recessive inheritance, a single copy of a mutated gene on the X chromosome is enough to cause a condition
Lyon hypothesis in females and why is it necessary
The Lyon hypothesis, also known as X-inactivation, explains how females, having two X chromosomes, compensate for the potential “double dose” of X-linked genes compared to males who have only one.
One of the two X chromosomes in females is randomly inactivated in each cell during early embryonic development, preventing a double expression of X-linked genes.
This inactivation is essential for maintaining a balanced expression of X-linked genes in both sexes.
MELAS syndrome in children and mtDNA
MELAS syndrome, caused by mutations in mitochondrial DNA (mtDNA), is a mitochondrial disorder that typically manifests in childhood, often with symptoms appearing between ages 2 and 10.
MELAS is inherited maternally, meaning it is passed down from the mother to her children.
Mitochondrial DNA inheritance
primarily inherited from the mother, meaning that most of the mtDNA in a child’s cells is derived from their mother’s egg.
Template strand is 3’-5’
Yes, the template strand of DNA is read in the 3’ to 5’ direction. This direction is necessary for the enzyme DNA polymerase to synthesize a new DNA strand in the 5’ to 3’ direction, ensuring the new strand is complementary to the template.
Formation of the DNA polymerase initiation complex at core promotor in eukaryotes
- TFIID and the TATA box:
TFIID, a complex of proteins including TATA-binding protein (TBP), is the first to bind to the TATA box, a sequence-rich region in the core promoter. This interaction acts as the initial anchor for the assembly of the transcription machinery. - Recruitment of GTFs:
The binding of TFIID facilitates the recruitment of other general transcription factors, such as TFIIB, TFIIF, TFIIE, and TFIIH, to the promoter. These factors play various roles in unwinding the DNA, preparing it for transcription initiation, and recruiting RNA polymerase II. - Pol II recruitment:
Once the GTFs are assembled, RNA polymerase II (Pol II) is recruited to the promoter, forming the pre-initiation complex (PIC). - PIC and initiation:
The PIC is initially in a closed state, meaning the DNA around the transcription start site is still tightly bound. Before transcription can begin, the DNA must be unwound and the template strand loaded into the active site of Pol II, forming an open complex. This process requires the activity of some GTFs and other factors. - Initiation and elongation:
Once the open complex is formed, Pol II can initiate RNA synthesis, marking the beginning of the transcription elongation phase.
Enhancer (transcription)
a DNA sequence that increases the rate of gene expression. They are cis-acting elements, meaning they act on the same DNA molecule as the gene they regulate.
