Topic 2: Life Cycles and Eukaryotic Chromosomes Flashcards
What are eukaryotic life cycles?
the vast majority of eukaryotes are diploid, which means they have 2 copies of every chromosome
diploid (2n) phase –> meiosis –> haploid (n) phase –> fertilization –> diploid (2n) phase
What happens to the pairs of homologs in the eukaryotic life cycles?
pairs separated during meiosis
paternal and maternal homologs join in fertilization (n –> 2n)
what’s the point? –> generate genetic diveristy
What is spermatogenesis?
male gamete production
What is oogenesis?
female gamete production
What is the process of spermatogenesis?
spermatogonia (2n) in the testes, undergoes mitosis endlessly until entering prophase I
after prophase I it becomes a primary spermatocyte (2n)
after meiosis I is complete there are now two secondary spermatocytes (n)x2
after meiosis II is complete there are 4 spermatids (immature sperm)
they then mature into sperm
What is the process of oogenesis?
oogonium (2n) in the ovaries, undergoes mitosis endlessly until entering prophase I
after prophase I it becomes a primary oocyte (2n)
in meiosis I the cytoplasm is divided unequally, resulting in a secondary oocyte (n) and the first polar body
the secondary oocyte undergoes meiosis II where it divides into the ovum and the second polar body
once this ovum is in contact with sperm fertilization occurs and a zygote is (2n) formed
more energy is put into each gamete than in spermatogenesis
sperm penetration happens before meiosis II
When does the process of spermatogenesis occur in males?
spermatogonia are being made into sperm continuously from puberty onward
When does the process of oogenesis occur in females?
the process of oogonium being made into primary oocytes happens before birth, so all of a females primary oocytes are present at her birth
these primary oocytes are arrested in prophase I until puberty
after puberty one or two primary oocytes a month will resume mitosis until they run out
What are the steps of early development in humans?
- ovulation: primary oocyte being released and resuming meiosis
- fertilization: nuclei fusion, sperm penetration
- cleavage
- implantation, at about 6-7 days the cell hatches and digs into uterus walls
What is the alternation of generations?
both the diploid and haploid stages are multicellular
What is the life cycle of flowering plants and conifers?
gametophyte depends/lives inside the sporophyte
What is the male half of the plant life cycle?
the stamen contains microsporocytes (2n)
through meiosis the microsporocytes (2n) become four microspores (n)
through mitosis the microspores become mature pollen grains called microgametophytes (n)
they contain 2 sperm nuclei and 1 tube nuclei
What is the female half of the plant life cycle?
the female pistil contain the megasporocytes (2n)
through meiosis the megasporocytes (2n) become four megaspores (n)
through mitosis the megaspores become eight nuclei megasporocyte
they contain 2 polar nuclei and 1 egg nuclei
What is double fertilization in the plant life cycle?
one sperm nuclei fuses with egg –> zygote (2n)
one sperm nuclei fuses with 2 polar nuclei –> endosperm (3n), this is the sterile, nutritive tissue that feeds plant embryo in seed
Why is yeast a food eukaryotic model?
unicellular
short life cycle (~90 min)
exists in both haploid and diploid form
easy to manipulate ploidy
all products of meiosis are in a single structure
grows easily in culture
What is the asexual haploid part of the yeast life cycle?
mating types: both a and alpha mating types, both contributing equal sized gametes so no male or female
mitosis of haploid cells: budding
What is the asexual diploid part of the yeast life cycle?
mitosis of diploid part of life cycle
What is the sexual part of the yeast life cycle?
nuclear fusion (not fertilization): two equal sized gametes, one from a and alpha
starvation induces meiosis –> haploid cultures
nutritive medium induces nuclear fusion –> diploid culture
What are the advantages to the life cycle of yeast?
recessive allele phenotypes can be observed in the haploid stage
allele interactions can be examined in the diploid stage
What is the ascus in the life cycle of yeast?
all products of individual meiotic divisions are kept together in the ascus
direct observation of products of single mitotic division
direct tracking of independent segregation of chromosomes and recombinarion
What do the nucleic acid synthesis rules apply to?
DNA replication in a cell
RNA synthesis in a cell
DNA/RNA synthesis in the lab
What are the nucleic acid synthesis rules?
- made of NTPs –> RNA and dNTPs –> DNA
- built in 5’–>3’, open 3’-OH is required in DNA/RNA pol
- made using ssDNA template
- complementary base pairing
- anti-parallel
What are centromeres on eukaryotic chromosomes?
attachment points for spindle
What are telomeres on eukaryotic chromosomes?
repetitive regions at the tips of chromosomes
What are the origins of replication on eukaryotic chromosomes?
where DNA synthesis begins
1000s of them
What is the end replication problem?
telomeres are required to prevent chromosome instability and loss of important genetic information at each round of replication
telomerase is active only in germ cells, early embryo cells, and proliferative somatic cells (i.e. bone marrow)
losing telomeres contributes to aging
How does telomerase build telomeres?
protein (polymerase action) + RNA enzyme (tandem repeat that matches g-rich overhang)
happens in early stages of life
How are large amounts of DNA packed into a cell?
DNA must remain accessible during interphase (DNA replication, RNA transcription, repair)
tightly packed and mobile M-phase (organized and separated)
chromatin = DNA complexed with protein
What is euchromatin?
chromatin condensation: less
location: chromosomes arms
types of sequences: unique sequence
presence of genes: many
when replicated: throughout S-phase
transcription: often, transcription is allowed
crossing over: common
What is heterochromatin?
chromatin condensation: more
location: centromeres and telomeres
types of sequences: repetitive sequence
presence of genes: few
when replicated: late S-phase
transcription: rarely, too compact for transcription
crossing over: uncommon
What is the structure of chromatin?
nucleosome: basic structure of chromatin
linker DNA
high-order chromatin structure: 30nm fiber, 300nm loops, 250nm wide fiber (listed from least to most dense)
What are the steps to forming the different levels of organization in chromatin?
- double helix
- DNA wraps around histones (nucleosomes), beads on a string (basic unit chromatin)
- coils up into 30 nm fiber
- loops into 300 nm loop domains
- folds up into 250 nm giber
- finally coils into a metaphase chromosome
What is a nucleosome?
the fundamental repeating unit of the chromatin
What is a histone hetero-octamer?
2 each of: H2A, H2B, H3, and H4
these are the four genes involved in making the protein
What is condensin?
work at the highest level of condensation
required to achieve metaphase chromosomes
work with a chromatid to compact them, required for max density seen at metaphase
What is a karyotype?
physical description of an individuals or species chromosomes
What does the human karyotype consist of?
22 pairs of autosomes, 1 pair of sex chromosomes (X and Y), written as [46, XY]
chromosomes are numbered largest to smallest (chr 1: 485 Mb, chr 22: 48 Mb)
What are metacentric chromosomes?
centromere right in middle
What are telocentric chromosomes?
only lower arms
What are acrocentric chromosomes?
very short arms on top
How is a chromosome squash used to obtain images of chromosomes?
cheek or blood sample
culture it –> put on slide –> squash it with coverslip
How is a stain used to obtain images of chromosomes?
trypsin removes chromatin and allows the Giemsa stain to penetrate and show banding of chromosomes
How do we get images of metaphase chromosomes?
karyotypes always describe metaphase chromosomes
block metaphase checkpoint –> checks spindle
block microtubes from forming spindle –> use a drug colchicine
What is the nomenclature of karyotypes?
we can identify both the chromosome number and the regions of the chromosome by using standard nomenclature
What is the nomenclature for chromosome number?
total number of chromosomes followed by number and type of sex chromosomes (XX or XY)
humans: 46,XX or 46,XY
What is the nomenclature for chromosomal number abnormalities?
sometimes you can have too many or too few chromosomes that can cause disease states
Down’s syndrome: 47,XX,+21
Turner’s syndrome: 45,X or 45,XO
Cri-du-chat: 46,XX,-5p
What are the arms on a chromosome?
p: petite arm
q: long arm
images are edited to have p arm always on top
What is g-banding on a chromosome?
Giemsa dye: light and dark banding
sometimes band number varies with the quality of the prep so scientists also use distinction of regions
What is the nomenclature for g-banding?
gene is 18p11.2, which means
chromosome 18
arm p
region 1
band 1
sub-band 2
