Genetics - Week 2 Flashcards
What are alleles?
different versions of the same gene
How might homologous chromosomes differ?
they may carry the same gene, but different alleles
What happens to the alleles after replication?
sister chromatids have identical alleles
What are genotypes?
combination of alleles in a single cell or single individual that relate to specific traits we are interested in
- alleles belonging to same gene are separated by a ‘/’
- alleles belonging to different genes are separated by a ‘;’
The Cell Cycle
What is interphase?
G1/S/G2
The Cell Cycle
When does DNA replication occur?
interphase
What is the goal of mitosis?
- to produce daughter cells that are genetically identical to parent cell
- asexual reproduction (no gametes are produced)
Mitosis
Describe the process.
prophase
metaphase
anaphase
telophase
Mitosis
What occurs in metaphase?
allows splitting of sister chromatids to be shared between two daughter cells
What happens go chromosomes after DNA replication?
the number of chromosomes do not change, but results in the formation of sister chromatids (which share one centromere)
Mitosis
What happens in anaphase?
kinetochore microtubules pull the sister chromatids away from each other, breaking them into two individual chromosomes
number of chromosomes has doubled
Mitosis
What happens in early telophase?
- chromosomes are still contained within ONE cell
How is a cell replicated?
by undergoing several cell phases in the cell cycle
What is the process of the cell cycle?
- Gap 1 (G1): phase for growth
- G0: resting phase - cell division ceases
- Synthesis (S): phase for DNA replication
- Gap 2 (G2): phase for more growth
- Mitosis and Cytokinesis
The Cell Cycle
What are checkpoints?
ensure that everything is progressing normally before entering the next stage
The Cell Cycle
Where are the checkpoints?
- one between G1/S
- one in G2
- one in mitosis
The Cell Cycle
What happens if any mistakes are found in DNA?
it’s important to fix them before the cell divides in mitosis so that the errors aren’t present in the daughter cells
The Cell Cycle
When will the cell still undergo mitosis even though there is some sort of defect?
in some cases, mutations occur that will allow the cell to undergo mitosis, despite such defects
When can cancer occur?
when checkpoints fails to function properly, allowing the cell to divide uncontrollably
What is a tumour (neoplasm)?
cluster of cells growing abnormally, but have not yet spread to other tissues
What is metastasis?
occurs when abnormal cells break off and travel through the bloodstream, spreading to other tissues throughout the body
Describe cancer cells.
- grow/divide when they aren’t supposed to
- don’t die when they are supposed to
- invade parts of the body they aren’t supposed to
What can cancer be caused by?
an accumulation of mutations and/or nondisjunction events
What are mutations?
permanent change in nucleotide sequence
What are mutations caused by?
errors in:
- DNA replication: incorrect bases are added to new DNA strand
- DNA repair: ironically, sometimes when the DNA repair machinery is trying to fix a problem, it can make mistakes - if unchecked and isn’t corrected, it can lead to mutations as well
When does nondisjunction occur?
when chromosomes don’t separate properly during mitosis or meiosis in anaphase, resulting in daughter cells with either too many (or missing) chromosomes
What consequences does nondisjunction have on the genomes of the daughter cells?
one daughter cell is going to have more than the usual number of copies of a gene, while the other daughter cell is missing a copy
- parent cell is diploid (2n=2)
- one daughter cell is haploid (n=1)
- one daughter cell is triploid (3n=3)
this can have detrimental results on an organism
What can nondisjunction cause in humans?
- down syndrome: experience physical growth and cognitive delay
- turner syndrome: affects development in females and a common feature is short stature in affected individuals, some experience loss of ovarian function
What are tumour suppressor genes?
act to slow down cell division, repair DNA replication errors, or start apoptosis (programmed cell death)
if both tumor suppressor genes are affected by mutation or lost via nondisjunction, this results in an inability to prevent tumor growth
Mitosis vs. Meiosis
How many cell divisions are there?
MITOSIS: only one cell division (PMAT)
MEIOSIS: two cell divisions (at end of meiosis I and meiosis II)
Mitosis vs. Meiosis
What are the ploidy levels of parent and daughter cells?
MITOSIS: ploidy level is the same between parent and daughter cells (ie. parents were diploid, so are the daughter cells)
MEIOSIS: daughter cells have half of the chromosomes compared to the parents (ie. parents were diploid, daughter cells are haploid)
Mitosis vs. Meiosis
Describe the pairing of homologs.
MITOSIS: no pairing of homologs
MEIOSIS: homologs pair up during prophase I (genetic recombination takes place)
Mitosis vs. Meiosis
Describe genetic recombination.
MITOSIS: no crossing over or genetic recombination occurs (parent and daughter genotypes are the same)
MEIOSIS: homologs line up across one another during metaphase I, resulting in independent assortment of chromosomes, crossing over of homologs may occur in prophase I
What is the result of meiosis?
daughter cells are not identical to parent cell, and allows for production of genetically variable offspring
What is the process of meiosis?
chromosomes align and are split up in such a way that each daughter cell receives only half of all the genetic material in the parent cell
What is the function of meiosis?
for the purposes of sexual reproduction, the diploid genome has to be split into two haploid genomes
- if the gametes are not haploid with all genes properly represented, then when two gametes fuse the zygote will have an incorrect number of chromosomes/gene copies
What are the two processes that allow for genetic variation?
independent assortment
crossing over
When does crossing over occur?
prophase I (in meiosis I)
How does crossing over occur?
- specialized proteins cause deliberate breakage of chromatids
- during chromatid repair, non-sister chromatids from homologous chromosomes can cross over: if this occurs, then genetic recombination of chromosomes can result
- if sister chromatids cross over, there is no genetic recombination as sister chromatids are replicates of one another
What is a locus?
specific location of a gene on chromosome
