Topic 2: Life Cycles and Eukaryotic Chromosomes Flashcards
Fertilization causes a change from the __________ phase to the __________ whereas meiosis causes a change from the ___________ to the ___________ phase
Haploid –> diploid
Diploid –> haploid
What joins during fertilization
Paternal and maternal homologs
Meiosis produces what? Which undergoes _______________ to produce a _________.
Produces eggs and sperm (n)
Undergoes fertilization to produce a zygote (2n)
What happens to the zygote?
Undergoes mitosis, becomes an adult then undergoes meiosis
Male vs female production of gametes
Male = spermatogenesis
Female = oogenesis
What is endlessly undergoing mitosis in the testes of males?
Spermatogonia (2n)
Spermatogonia enter ___________ to become ___________
Prophase 1
Primary spermatocyte (2n)
The primary spermatocyte undergoes ___________ to produce _____________________
Meiosis 1
Secondary spermatocytes (n) x2
Secondary spermatocytes undergo ______________ to produce _____________
Meiosis 2
4 spermatids (immature sperm)
the spermatids develop into what
4 mature sperm
Transformations in spermatogenesis
Spermatogonia (2n) -> primary spermatocyte (2n) -> secondary spermatocytes (n) -> 4 spermatids -> 4 mature sperm
What is undergoing mitosis in women
Oogonium (2n)
Oogonium enters __________ to become _______________
Prophase 1
Primary oocyte (2n)
Primary oocytes undergo _________________ to become _______________ and __________________
Meiosis 1
Secondary oocyte (1n) and 1st polar body
Secondary oocytes undergo _____________ to become __________________ and _______________
Meiosis 2
Ovum (n) and 2nd polar body
Ovum undergoes _____________ to become a ____________
fertilization, zygote
When does sperm penetration occur
Before completion of meiosis 2 (before ovum), triggers meiosis 2
What happens in women before birth
Oogonium becomes primary oocyte, then oogenesis arrests in prophase 1
When does meiosis resume in women
After puberty, one or two primary oocytes will resume meiosis per month until they run out
Morula vs blastocyst
Morula = solid ball of cells
Blastocyst = hollow ball
Major difference in human life cycle and plant life cycle
Diploid and haploid stages are multicellular in plants
Diploid stage is called _______________ and haploid stage is called ______________ (plants)
Sporophyte (2n)
Gametophyte (1n)
What do gametophytes produce? How? Vs sporophytes?
Gametophytes produce gametes through mitosis
Sporophytes produce spores (1n) through meiosis
What happens to gametes after mitosis (plants)
fusion into zygote (2n)
Ploidy of gametes, spores, zygote
Gametes = n
Spores = n
Zygote = 2n
In most flowering plants/conifers, how large is the sporophyte and where does it live? Gametophyte?
Gametophyte = tiny, depends on/lives in the sporophyte
Sporophyte = larger, leafy part
Micro vs mega in plants
Micro = males
Mega = females
microsporocytes (2n) undergo ____________ and become _______________
meiosis
4 microspores (n)
Microspores undergo _________ and become _____________
mitosis
mature pollen grains (microgametophytes)
Where is the ovary located in plants
Inside the pistil
Megasporocytes (2n) undergo _________ and become _______________
meiosis
megaspores (n)
Megaspores undergo ______________ and become ________________
mitosis
Megagametophyte (8 nuclei)
Megasporophytes contain 8 nuclei, the three important ones are…
2 polar nuclei
1 egg nuclei
How do plant zygotes form
One sperm nuclei fuses with the egg
Two parts of double fertilization
- one sperm nuclei fuses with egg = zygote
- one sperm nuclei fuses with two polar nuclei = endosperm (3n)
What does the endosperm provide
Nutritive tissue that feeds the plant embryo in the seed
2n, genome size, # genes of yeast
2n = 32 / 10Mb / 6144 genes
Advantages of yeast
Unicellular
Short cell cycle
Easy manipulation of ploidy
All products of meiosis in a single structure
Grows easily in culture
Two mating types of yeast, what part of the life cycle do they occur in
a and alpha
Sexual and asexual haploid part of life cycle
Mitosis of haploid and diploid cells occurs through what in yeasts?
Budding
Two components of the sexual cycle of yeast
- nuclear fusion (two equal sized gametes from a and alpha)
- meiosis
What is the ascus
Container found in yeasts containing ascospores (undergo budding, meiosis, fusion)
How do induce haploid culture in yeasts? Diploid?
n = induce meiosis via starvation
2n = induce nuclear fusion via nutritive medium
Advantages of the sexual life cycle of yeasts
Can induce meiosis to observe the recessive allele phenotype
Where are products of individual meiotic division kept in yeast
Ascus
Five rules of nucleic acid synthesis
- DNA made of dNTPS, RNA made of NTPS
- Built in 5’ to 3’ direction
- Made using ssDNA template
- Complementary base pairing
- Run anti-parallel
What is required by DNA/RNA polymerase on the DNA strand
Open 3’ OH
Which bases are purines? Pyrimidines? Which ones pair
Purines = AG
Pyrimidines = CT
A-T
C-G
What are the parts of the eukaryotic chromosome
Centromere (attachment points for spindle microtubules)
Telomeres (repetitive regions at tips of chromosomes)
Origins of replication (where DNA synthesis begins)
How many origins of replication on eukaryotic chromosomes
Thousands
Why are telomeres required on chromosomes
Prevent chromosomes instability and loss of important genetic information at each round of replication
- are repetitive, encode no genes so can be lost
What enzyme builds telomeres
Telomerase
Two parts of telomerase, their functions
- Protein = polymerase action
- RNA enzyme = tandem repeat that matches g-rich overhang
Difference in packing in interphase vs M-phase. Why?
Interphase = loosely packed to allow for DNA replication, RNA transcription, repair processes
M-phase = tightly packed and mobile to keep organized/separated
Characteristics of euchromatin vs heterochromatin (condensation, location, type of seq, presence of genes)
E = less compact, chromosome arm, unique seq, many genes, transcription occurs
H = more compact, centromeres/telomeres/other, moderately/highly repetitive, few genes
Aspects of chromatin structure
Nucleosome, linker DNA, 30nm fiber, 300nm loops, 250nm wide fiber
Most dense area of chromatin
250 nm wide fiber
What is a nucleosome
DNA wrapped around histones, many joined = basic repeating unit of chromatin
Sequence of 30nm fiber, 250nm wide fiber and 300nm loop
30->300->250
Slide 32**
chromatin structure
What are the four genes involved in making histones
H2A, H2B, H3, H4
What is condensin
Protein that work at the highest level of compaction (compacts chromatid), required to achieve metaphase chromosome (max density)
Cohesin vs condensin
cohesin = work btw sister chromatids to keep them together
condensin = work within a chromatid to compact it (max density for metaphase)
What is a karyotype
Physical description of an individual or a species’ chromosomes
Human karyotype consists of…
22 pairs of autosomes
1 pair of sex chromosomes (XX/XY)
Is X the large or small chromosome? Male or female
X is large, female
What are metacentric, telocentric and acrocentric chromosomes
Metacentric = centromere in the middle
Telocentric = only bottom half of chromosome (?)
Acrocentric = centromere very close to top of chromosome
What does the giemsa stain show us
Banding of chromosomes
How do we arrest a chromosome at metaphase
Block metaphase checkpoint (which checks the spindle apparatus). Prevents microtubules from forming spindle. Use drug (colchicine)
Karyotype nomenclature for humans? Chimps?
46, XX or 46, XY
48, XX or 48, XY
List three chromosomal abnormalities, their nomenclature
Down syndrome: 47, XX +21 (3 copies of chr 21)
Turner’s syndrome: 45, X (whole/partial missing X chr)
Cri-du-chat: 46, XX, -5p (part of chromosome 5 missing)
Parts of the chromosome
Arms (p and q)
G-banding
Subbands
regions
P vs q arms
P = petite arm (top)
Q = long arm
