Chromosomal Basis of Heredity Flashcards
The first cells
Prokaryotes
Cells that lack a nucleus or membrane-bound organelles: nucleus, ER, mitochondria, golgi apparatus, chloroplast
includes bacteria
Prokaryotes
What is the shape of a prokaryote chromosome
Circular
Where is the DNA found in prokaryotes
Nucleoid region
What organelle make proteins
Ribosomes
Eukaryotes contain 3 basic cell structures:
- Nucleus
- Cell membrane
- Cytoplasm with organelles
Fluid, jelly-like substance between the cell membrane and the nucleus in which organelles are suspended
Serves as matrix substance in which chemical reactions occur
Cytoplasm
Granular particles composed of protein and RNA
Synthesize proteins
Ribosomes
Cluster of flattened membranous sacs that synthesize carbohydrates and packages molecules for secretion, secretes lipids and glycoproteins
Golgi complex
Membranous sacs with folded inner partitions that release energy from food molecules and transform energy into usable ATP
Mitochondria
Membranous sacs that digest foreign molecules and worn and damaged organelles
Lysosomes
Metabolizes nonpolar compounds and stores Ca2+ in striated muscle cells
Agranular (smooth) endoplasmic reticulum
Which ER assists in protein synthesis
Granular (rough) endoplasmic reticulum
Spherical membranous vesicles that contain enzymes that detoxify harmful molecules and break down hydrogen peroxide
Peroxisomes
Nonmembranous mass of two rod-like centrioles that helps organize spindle fibers and distribute chromosomes during mitosis
Centrosome
Membranous sacs that store and release various substances within the cytoplasm
Vacuoles
Thin, hollow tubes that support cytoplasm and transport materials within the cytoplasm
Microfilaments and microtubules
Minute cytoplasmic projections that extend from the cell surface that move particles along cell surface or move the cell
Cilia and flagella
Double-layered membrane that surrounds the nucleus, composed of protein and lipid molecules
Supports nucleus and controls passage of materials between nucleus and cytoplasm
Nuclear envelope
Fibrous strands composed of protein and DNA that contains genetic code that determines which proteins (including enzymes) will be manufactures by the cell
Chromatin
theory that states that some organelles within cells were at one time free living cells themselves
Supporting evidence included organelles
with their own DNA:
Chloroplast and Mitochondria
Endosymbiotic theory
Mitochondria Come from cytoplasm in the EGG cell during fertilization
Therefore …
You inherit your mitochondria from your mother
Most eukaryotes have between __ and
___ chromosomes in their body cells
10 and 50
Human body cells have __ chromosomes or __ identical pairs
46
23
Each chromosome is composed of a single, tightly coiled DNA molecule
Chromosomes can’t be seen when cells aren’t dividing and are called chromatin
Duplicated chromosomes are called ___________ & are held together by the ___________
chromatids
centromere
The shorter arm of the chromatid is the
p arm
The longer arm of the chromatid is called the
q arm
shape of the chromosome during anaphase is determined by the position of the centromere during metaphase
centromere is located in the middle
Metacentric
centromere is located between the middle and the end (3/4)
Submetacentric
centromere is located close to the end
Acrocentric
centromere is located at the end
Telocentric
When are sister chromatids formed
Formed during the DNA replication in the S phase of the Interphase
Homologous chromosomes do not stick together whereas sister chromatids are joined by their centromere
How many DNA strands do Homologous chromosomes have
4
How many DNA strand do sister chromatids have
1
Chromosomes that have identical gene sites along their lengths : locus
identical in the traits that they influence and in their genetic potential
Homologous Chromosomes
diploid organism - biparental inheritance
* two copies of each gene as a consequence of inheritance from two parents
Homologous chromosomes exceptions
- Sex-determining chromosomes
-often not homologous in size, centromere placement, arm ratio, or genetic content
which sex chromosome is smaller and lacks most of the gene loci contained on the X
Y chromosome
X and Y chromosomes are not strictly homologous
- contain homologous regions and behave as homologs in meiosis so that gametes produced by males receive either one X or one Y chromosome
Pseudoautosomal regions
Types of cell reproduction
Asexual reproduction
ex. Mitosis and Binary Fission
Sexual reproduction
ex. Meiosis
- Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission
- Single chromosome makes a copy of itself
-Cell wall forms between the chromosomes dividing the cell
Five phases of cell cycle
- G1 - primary growth phase
- S - synthesis; DNA replicated
- G2 - secondary growth phase
* collectively these 3 stages are called interphase - M - mitosis
- C - cytokinesis
Time spent by cell to undergo Interphase and Mitosis
Interphase
G1 = 5 hrs
S = 7 hrs
G2 = 3 hrs
Mitosis = 1 hr
P = 36 mins.
M = 3 mins.
A = 3 mins.
T = 18 mins.
Phase wherein:
1st growth stage after cell division
Cells mature by making more cytoplasm & organelles
Cell carries on its normal metabolic activities
Interphase - G1 stage
Stage wherein:
Cells remain viable and metabolically active
Not proliferative
Cancer cells avoid entering or pass it very quickly
Other cells enter and never reenter the cell cycle
Other cells can be stimulated to return to G1 and reenter the cell cycle
G0 stage
✓Synthesis stage
✓DNA is copied or replicated
Interphase - S stage
2nd Growth Stage
Occurs after DNA has been copied
All cell structures needed for division are made (e.g. centrioles)
Both organelles & proteins are synthesized
Interphase - G2 stage
✓In plant cells, ______ forms at the equator to divide cell
✓In animal cells, _____ forms to split cell
cell plate
cleavage furrow
Division of nucleus is also called
Karyokinesis
How many stages does mitosis have
4
Chromosomes are extended and uncoiled, forming chromatin
Interphase
Chromosomes coil up and condense, centrioles divide and move apart
Prophase
Chromosomes are clearly double structures; centrioles reach the opposite poles; spindle fibers form
Prometaphase
Centromeres align on metaphase plate
Metaphase
Centromeres split and daughter chromosomes migrate to opposite poles
Anaphase
Daughter chromosomes arrive at the poles; cytokinesis commenses
Telophase
What happens in prophase
-Nuclear membrane disintegrates and nucleolus disappears
-Chromosomes condense
-Mitotic spindle begins to form and is complete at the end of prophase
-Kinetochores begin to mature and attach to spindle
What happens in Metaphase
-Kinetochores attach chromosomes to mitotic spindle and align them along metaphase plate at equator of the cell
Sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers
Anaphase
multi-subunit protein complex that holds together sister chromatids
Cohesin
Once properly attached to the spindle fibers, cohesion is degraded by this enzyme
Separase
protects cohesion from being degraded by separase at the centromeric regions
Shugoshin
Anaphase disjunction:
For complete disjunction to occur:
(1) shugoshin must be degraded, reversing its protective role
(2) the cohesin complex holding the centromere region of each sister chromosome is then cleaved by separase
(3) sister chromatids of each chromosome are pulled toward the opposite poles of the cell
What happens in Anaphase
-Kinetochore microtubules shorten, separating chromosomes to opposite poles
-Polar microtubules elongate, preparing cell for cytokinesis
What happens in Telophase
-Chromosomes reach poles of each cell
-Kinetochores disappear
-Polar microtubules continue to elongate, preparing cell for cytokinesis
-Nuclear membrane reforms
-Nucleolus reappears
-Chromosomes decondense
✓Means division of the cytoplasm
✓Division of cell into two, identical halves called daughter cells
Cytokinesis
cell division cycle (cdc) mutations was first discovered in which organism
Yeasts
= normal products of many of the mutated genes are enzymes that can add phosphates to other proteins.
* serve as “master control” molecules functioning in conjunction with proteins called cyclins
Kinases
- bind to these kinases (creating cyclin-dependent kinases), activating them at appropriate times during the cell cycle.
- activated kinases then phosphorylate other target proteins that regulate the progress of the cell cycle
Cyclins
G1/S checkpoint
- monitors the size the cell has achieved since its previous mitosis and also evaluates the condition of the DNA.
- If cell has not reached an adequate size or if the DNA has been damaged, further progress through the cycle is arrested until these conditions are “corrected”
- If both conditions are “normal” at G1/S, then the cell is allowed to proceed from G1 to the S phase of the cycle
G2/M checkpoint
- where DNA is monitored prior to the start of mitosis
- If DNA replication is incomplete or any DNA damage is detected and has not been repaired, the cell cycle is arrested
M checkpoint
- final checkpoint sometimes referred to as the _________
- the successful formation of the spindle fiber system and the attachment of spindle fibers to the kinetochores associated with the centromeres are monitored
- If spindle fibers are not properly formed or if attachment is inadequate, mitosis is arrested
Spindle Assembly Checkpoint
are special proteins that increase the chance that a normal cell develops into a tumor cell
Oncogenes
✓Original cell is diploid (2n)
✓Four daughter cells produced that are monoploid
(1n)
✓Occurs in the testes in males (Spermatogenesis)
✓Occurs in the ovaries in females (Oogenesis)
✓Occurs in our germ cells that produce gametes
Meiosis
2 meiotic divisions
Reductional division
Equational division
is the process of duplicating a chromosome
Replication
Replicated copies are called
sister chromatids (same genes, same allele)
Same genes, different alleles are calles
Homologs
Substages of Meiotic Prophase I
- Leptonema
= Interphase chromatin material begins to condense
= Chromosomes still extended, become visible w/ chromomeres, localized condensations that resemble beads on a string
= homology search: precedes and is essential to the initial pairing of homologs, begins - Zygonema
= chromosomes continue to shorten and thicken
= rough pairing of homologous chromosomes
= synaptonemal complex begins to form between the homologs - Pachynema
= synapsis, a more intimate pairing
= each homolog now evident as a double structure
= each bivalent contains four member chromatids
= tetrad, contains two pairs of sister chromatids - Diplonema
= within each tetrad, each pair of sister chromatids begins to separate. - Diakinesis
= chromosomes pull farther apart
= nonsister chromatids remain loosely associated at the chiasmata
= separation proceeds, chiasmata move toward the ends of the tetrad
= nucleolus and nuclear envelope break down
a point where nonsister chromatids have undergone genetic exchange through crossing over
Chiasma
Homologous pairs of chromosomes align along the equator of the cell
Metaphase I
Homologs separate and move to opposite poles
Sister chromatids remain attached at their centromeres.
Anaphase I
Nuclear envelopes reassemble.
Spindle disappears
Cytokinesis divides cell into two.
Telophase I
Only one homolog of each chromosome is present in the cell.
Meiosis II
Meiosis II produces gametes with one copy of
each chromosome and thus one copy of each
gene.
Nuclear envelope fragments.
Spindle forms.
Prophase II
Chromosomes align along equator of cell
Metaphase II
Sister chromatids separate and move to opposite poles
Anaphase II
Nuclear envelope assembles
Chromosomes decondense.
Spindle disappears.
Cytokinesis divides cell into two.
Telophase II
Reductional division results in dyads
Equational division results in monads
order of substages in Meiotic prophase I
Leptonema
Zygonema
Pachynema
Diplonema
Diakinesis
are the germ cells that will eventually
develop into the mature sperm or egg
Spermatogonia and oogonia
Primary spermatocyte or oocyte:
*the first step in this development is the
duplication of homologous chromosomes
to get ready for meiosis
Secondary spermatocyte or oocyte:
* the first meiotic division separates the homologous chromosomes from each parent
Spermatids or eggs:
* the second meiotic division separates the 2 chromatids and creates 4 haploid cells
In males, this eventually produces _ sperm cells by the process of spermiogenesis
4
In females, it produces _ egg and _ polar
bodies. This allows the egg to retain
more cytoplasm to support early stages
of development
1
3
Meiosis generates tremendous genetic diversity. How many different types of gametes can be generated by an individual (male or female) with 23 different chromosomes?
More than 2^23 or 8,000,000 different gametes
In males, the spermatogonia enter meiosis and produce sperm from puberty until death.
The process of sperm production takes only a few weeks.
Each ejaculation has 100 to 500 million sperm.
In females, the first meiotic division starts before birth but fails to proceed.
It is eventually completed about one month before ovulation in humans.
In humans, the second meiotic division occurs just before the actual process of fertilization occurs.
all meiosis is ended in females at menopause.
Each pair of chromatids is connected by __________.
axial proteins
The 2 homologous chromosomes are held
together closely by ________.
central element proteins (synaptonemal complex)
Trisomy 21
Failure of 2 chromatids to separate during meiosis II -> results in one oocyte receiving 2 instead of 1 chromatid
It results in short stature, round face and mild to severe mental retardation
Down syndrome
Immature egg called
oocyte
matured oocyte is called
ovum (egg)
OOCYTES HAVE A VERY SMALL NUCLEUS / CYTOPLASM RATIO
Ribosomal RNA genes are often amplified in oocytes. This allows more templates to
transcribe more rRNA.
Dense nonmembranous mass composed of protein and RNA molecules
Produces rRNA for ribosomes
Nucleolus
Surrounded by cell membrane & cell wall
peptidoglycan
Many mutations that exert an effect at one or another stage of the cell cycle
Cell Division Cycle (cdc) Mutations
A __________ forms that contains enzymes for cutting and splicing DNA.
recombination nodule
Chromosomes are cut and joined crosswise at points called _______, seen when they separate.
chiasmata
Chromosomal aberrations can be caused by..
nondisjunction
translocation
- Chromosomes fail to separate during oogenesis or spermatogenesis
- Inherit too many or too few X or Y chromosomes
Nondisjunction
-> 45,X or 45,X0
-> loss of 2nd sex chromosome
-> affects females
-> short stature, reduced functioning of ovaries
Turner syndrome
-> 47,XXY
-> male has an extra X chromosome
-> affects testicular growth, resulting in smaller than normal testicles = lower production of testosterone
-> reduced muscle mass, body and facial hair, enlarged breast tissue
Klinefelter syndrome
Trisomy 13
-> severe intellectual disability and physical abnormalities in many parts of the body
-> heart defects, brain/spina cord abnormalities, microphthalmia, extra fingers/toes, cleft lip with or without palate, and hypotonia
-> deafness and cardiac anomalies
Patau syndrome
cause of chromosomal aberration:
- bits of chromosomes that are re-attached to other chromosomes
translocation
- Extra complete sets of chromosomes
- 3N, 4N, 5N, etc.
Polyploidy
- Extra or missing single chromosomes
- 2N + 1, 2N -1, etc
aneuploidy
Changes in the location of genes
- inversions: 180o rotation
- translocations: exchange
- transpositions: gene “hopping”
- Robertsonian changes: fissions or fusions
prenatal test that involves extracting a small amount of amniotic fluid from the uterus to assess the health of the fetus
performed during 2nd trimester = week 14-17
Amniocentesis
*Genotype is XXX (47 chromosomes, extra X, trisomy)
Super Female or Triple X Syndrome
▪Genotype is XYY (47 chromosomes, extra Y, trisomy)
▪Males only (1 in a 1000)
▪Usually tall (above 6 feet), slender and generally appear and act normal.
▪Produce high levels of testosterone. During adolescence they usually have severe facial acne and are poorly coordinated. They are usually fertile.
▪May be: antisocial and/or aggressive and may have below average intelligence/learning difficulties.
Super Male or XYY Syndrome
Trisomy 18
Multiple congenital malformation of many organs, malformed ears, small mouth and nose with general elfin appearance.
90% die in the first 6 months.
Edward’s syndrome
provides biochemical identity at the
surface of cells
glycocalyx or cell coat
The portions of DNA that encode rRNA are collectively referred to as the
nucleolus organizer region, or the NOR
In the cytoplasm, a nonparticulate, colloidal material referred to as the ______ surrounds and encompasses the cellular organelles
cytosol
what proteins are microfilaments derived from
actin
Collectively, the genetic information contained in a haploid set of chromosomes constitutes the ________ of the species
genome
the shortest stage of mitosis
anaphase
