Exam 4 Flashcards
Cell Division
The basis of reproduction, growth, and regeneration/repair
Four Division Events in Organisms
- Cell Division Signals
- DNA Replication
- DNA Segregation
- Cytokinesis
Binary Fission
The way in which prokaryotes divide
What are the signals for prokaryotes to divide by binary fission
Signals to divide are usually external factors such as environmental conditions and nutrient concentration
Does cell division always occur in eukaryotes if internal/environmental conditions are suitable for cell division?
No; commitment to divide depends on integration of extracellular and intracellular information
Steps of the Cell Cycle
G1, Interphase, G2, Mitosis (M phase)
In which phase of the cell cycle do eukaryotic cells divide
Eukaryotic cells only divide in the M phase of the cell cycle
Cycline-Dependent Kinases (CDKs)
Controls progress through the cell cycle; when activated, Cdk phosphorylates targets; when phosphorylated, these targets cause DNA replication enzymes to activate which makes S phase begin
Cdks are inactive without specific
Cyclines; each CDK is activated by binding to a specific cycline through allosteric regulation
What is each phase of the cell cycle characterized by
The activity of specific combinations of cyclin/Cdk
Restriction Point (R)
A control point in the cell cycle; progress past the restriction point depends on the phosphorylation of retinoblastoma protein (RB) by CDK4
Cell Cycle Checkpoints
Regulates progress through the cell cycle through cyclin-CDKs
Pass M checkpoints if
- DNA has attached to spindle
- DNA has been properly separated
- Mitotic cyclin is absent
Pass G1 checkpoints if
- Cell size is adequate
- Nutrients are sufficient
- Social signals are present
- DNA is undamaged
Pass G2 checkpoint if
- DNA is replicated successfully
- DNA is undamaged
- Activated mitotic cyclin is present
What is a key to regulating cell division
Since progress through the cell cycle depends on CDKs, regulating CDKs is a key to regulating cell division
Where is the genome stored
In chromosomes
Ori
Site of DNA replication in prokaryotes
How many chromosomes do prokaryotes have
One circular chromosome
How do prokaryotes replicated their DNA
Through theta replication
How many chromosomes do humans have
46 linear chromosomes
True or false: eukaryotic DNA replication has multiple origins
True
Sister Chromatids
Result of DNA replication; two identical copies of cell’s genetic material; they’re identical to one another in sequence and they’re physically attached
Chromatids vs chromosomes
Chromatids share a centromere, chromosomes have their own
When does eukaryotic DNA replication occur
S phase of the cell cycle
Cohesin
Protein complex that holds together sister chromatids; in G2, sister chromatids are held together along their length by cohesin
When is cohesin removed (except at centromere)
In prophase cohesin is removed except at the centromere, where the chromatids are held together
Mitosis
Allocates chromosomes into two new genetically identical nuclei in eukaryotes
Mitotic Spindle Apparatus
Consists of microtubules, moves DNA by binding to the kinetochore at the centromere of each sister chromatid
Kinetochore
A complex of proteins attached to the centromere
What is the orientation of the spindle and the direction DNA moves in determined by
The centrosome
What is the centrosome made up of
Two centrioles, which are mostly made of tubulin
Prophase/prometaphase of mitosis
Nuclear envelope is broken down and spindle is assembled
Metaphase of mitosis
Chromosomes line up at the metaphase plate
Anaphase of mitosis
First, the cohesin that holds sister chromatids together is removed by separase, allowing the sister chromatids to separate; then, daughter chromsomes are pulled to opposite poles of the cell
What is separase controlled by
The M phase Cdk-cyclin
What are sister chromatids called after they’re separated
Daughter chromosomes
Telophase of mitosis
The spindle dissolves, DNA decondenses, and the nuclear envelope re-forms
Cytokinesis in mitosis (animal cells)
Actin-myosin interactions pull plasma membrane inward to split the cell in two
Somatic Cells
Cells of the body; they’re made from mitosis
Diploid Cells
Cells that have two version of each chromosomes; they can have up to two versions of the same gene (alleles)
Alleles
A specific sequences of genes; versions of a gene
Heterozygous Cell
Has two different alleles of the same gene
Heterozygous Cell
Has the same allele of the same gene
Homologous Chromosomes
Chromosomes that share the same features but may contain different alleles
How many homologous pairs of chromosomes do humans have
22
Gametes
Egg and sperm cells; they only have one copy of each chromosome; haploid
Haploid Cells
Only have one copy of each chromosome
What yields a diploid cell
Union of haploid gametes at fertilization
Meiosis
How we make 4 haploid gametes from diploid cells; two nuclear divisions lead to the formation of haploid gametes that are genetically distinct
Starting point of both mitosis and meiosis 1
Duplicated chromosomes from S phase
Meiosis 1
Homologous chromosomes separate
Prophase 1 of Meiosis
Homologous chromosomes pair up along their lengths (synapse) so they can align together in metaphase 1 (creates nonsister chromatids)
Chiasmata
Regions of attachment that form between nonsister chromatids
True or false: nonsister chromatids may have different alleles
True
In heterozygous individuals, do nonsister chromatids have identical alleles?
No
Crossing Over
Allowed by synapsis; contributes to genetically diverse products in meiosis; results in recombinant chromatids that aren’t found in parents
What does meiosis 1 being a reductive division mean
One diploid parent cell becomes two haploid cells in meiosis 1
Meiosis 2
Sister chromatids separate; phases are like mitosis but with recombinant chromatids
Blending Inheritance
One of the two hypotheses for inheritance that emerged; in 1800s people thought that inheritance involved blending of parental traits; all future off spring would be the result of that blend
Particulate Inheritance
One of the two hypotheses for inheritance that emerged; proved by Gregor Mendel in 1860s; showed genes don’t change from offspring
Genotype
The combinations of alleles in a cell
Phenotype
The physical manifestation of alleles in a cell
Trait
Specific form of a characteristic (character: pea color, trait: yellow)
What is the molecular basis of dominance
Many possible reasons; one is that genes determine phenotype through the proteins that they encode
What yields a diploid cell
Union of haploid gametes at fertilization
DNA makeup
Exactly 50% of our DNA is from our egg parent and 50% is from our sperm parent
Monohybrid Cross
Two homozygous (true-breeding) parents with different traits are bred to produce all heterozygous F1s, which are crossed to each other
When does segregation/separation of alleles occur
the two alleles of a gene in any diploid individual separate during meiosis; each gamete receives 1 allele of each gene
Monohybrid cross F2 ratios
3:1 phenotypic ratio and 1:2:1 genotypic ratio (YY: Yy: yy)
True or false: dominance of an allele does not mean that it is more fit or more common in population
True
Mendel’s Law of Segregation
The two alleles of a gene in any diploid individual separate during meiosis; each gamete receives only allele of each gene
Punnett Square
Used to predict genotypes and phenotypes in a cross
Progeny
Offspring
Dihybrid cross
Looks at 2 genes with differing traits at same time
Dihybrid cross phenotypic ratio
9:3:3:1 (Both dominant traits:one dominant trait:other dominant trait: both recessive traits)
Mendel’s Law of Independent Assortment
Alleles of genes on different chromosomes don’t travel together during anaphase
Pedigrees
Used by geneticists to infer genotypes
True or false: for rare dominant traits, every affected person has an affected parent
True
True or false: for recessive traits, an affected individual may have unaffected parents
True
How do mutations arise
Through mistakes in DNA replication/repair (insertion, subsitution, deletion)
How do new alleles arise
Through mutations: stable, inherited changes in the genetic material
Consanginous Mating
Mating between relatives
Wild Type Allele
Most abundant allele in the population
Mutant Allele
AKA variants; alleles that aren’t most abundant in the population
True or false: Any one individual has two alleles at a locus, but there may be many alleles in the population
True
True or false: multiple alleles often show a hierarchy of dominance
True
Complete dominance
One of the types of dominance relationships; hybrid resembles one of the two parents
Incomplete dominance
Alleles are neither dominant or recessive- heterozygotes have intermediate phenotypes
Example of incomplete dominance
Purple and white fruit (p) makes heterozygote violet fruit (F1) and when those fruit breed, the original phenotypes reappear, along with violet heterozygotes (f2)
Codominance
Alleles produce phenotypes that are both present in the heterozygote
What defines the dominance in the relationship of two alleles
The phenotype of the heterozygote
Phenylketonuria
Results from a mutation in the gene that encodes PAH, an enzyme thats required to convert phenylalanine to tyrosine
Pleiotropy
When one allele has multiple phenotypic effects
Discrete Traits
Aka qualitative traits; have definable forms (ex: color)
Continuous Traits
Aka quantitative traits; have variable forms (ex: human height)
Quantitative Trait Loci (QTL)
The chromosomal regions that together determine complex characters; can contain one or more genes
Locus
A specific position on a chromosome
What does identifying loci do
Helps to improve crop yields, and understand disease susceptibility and behavior
How does environment affect phenotype
Light, temperature, nutrition, etc can affect expression of the genotype
True or false: Genes produce a phenotype through the proteins they encode
True
Melanocyte
Some of the genes that control coat color encode proteins that function in pigment-producing skin cells called melanocytes
Epistasis
In epistasis, the phenotypic expression of one gene is influenced by another gene; it occurs when one gene alters the phenotypic effect of another gene
Important F2 ratio (2 genes, recessive epistasis)
9:3:4 (dom:het:rec)
Dioecious
Only produces male/female gametes (most animals are dioecious)
In mammals and birds, what determines which gamete is produced
Sex chromosomes
Autosome
Chromosomes that aren’t sex chromosomes
SRY
A gene on the Y chromosome that determines male-ness
Sex-linked traits like colorblindness are caused by a mutation on which chromsomes
X chromosomes
Pedigrees of x-linked recessive traits
- Phenotype appears more often in males
- Heterozygous daughters are carriers
- A male with the mutation can only pass it to his daughters
- Mutant phenotype can skip a generation if it passes from a male to his daughter
Thomas Hunt
Demonstrated that genes are present on chromosomes (~1915)
Translocation
Occurs when a piece of one chromosome is moved onto another chromosome
What causes shuffling of alleles of genes on the same chromosome
Crossing over during meiosis 1 causes shuffling of alleles of genes on the same chromosome that is obvious in a heterozygote
How do recombinant genotypes form
When homologous chromosomes line up in metaphase 1, crossing over occurs as a result of homologous recombination
Recombination does not occur often between
Linked genes
How do we calculate the genetic distance between two genes
By calculating the frequency in which they recombine
Recombination Frequency (RF) Formula
RF = number of recombinants/total number of offspring
Relationship between closeness of genes and frequency of genes
The closer two genes are on the chromosome, the frequency that they will recombine is lower
What do linked genes not obey
The law of independent assortment
What is the maximum RF and what does it mean
50cM (50%); means genes are unlinked and will segregate independently
Where do you get the data to calculate an RF
From a test cross
Properties of linked genes
-Parentals>Recombinants (RF<50%)
- Linked genes must be syntenic and close together on the same chromosome so that they don’t assort independently
Properties of unlinked genes
- Parentals = recombinants (RF=50%)
- Occurs either when two genes are on different chromosomes or when they are sufficiently far apart on the same chromosome that at least one crossover occurs between them in every meiosis
Haplotype
A group of genes whose alleles are often inherited together; most commonly refers to a group of linked genes
