Topic 2: Life Cycles and Eukaryotic Chromosomes

Question 1

What are eukaryotic life cycles?

Answer 1

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

Question 2

What happens to the pairs of homologs in the eukaryotic life cycles?

Answer 2

pairs separated during meiosis

paternal and maternal homologs join in fertilization (n –> 2n)

what’s the point? –> generate genetic diveristy

Question 3

What is spermatogenesis?

Answer 3

male gamete production

Question 4

What is oogenesis?

Answer 4

female gamete production

Question 5

What is the process of spermatogenesis?

Answer 5

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

Question 6

What is the process of oogenesis?

Answer 6

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

Question 7

When does the process of spermatogenesis occur in males?

Answer 7

spermatogonia are being made into sperm continuously from puberty onward

Question 8

When does the process of oogenesis occur in females?

Answer 8

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

Question 9

What are the steps of early development in humans?

Answer 9

1. ovulation: primary oocyte being released and resuming meiosis
2. fertilization: nuclei fusion, sperm penetration
3. cleavage
4. implantation, at about 6-7 days the cell hatches and digs into uterus walls

Question 10

What is the alternation of generations?

Answer 10

both the diploid and haploid stages are multicellular

Question 11

What is the life cycle of flowering plants and conifers?

Answer 11

gametophyte depends/lives inside the sporophyte

Question 12

What is the male half of the plant life cycle?

Answer 12

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

Question 13

What is the female half of the plant life cycle?

Answer 13

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

Question 14

What is double fertilization in the plant life cycle?

Answer 14

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

Question 15

Why is yeast a food eukaryotic model?

Answer 15

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

Question 16

What is the asexual haploid part of the yeast life cycle?

Answer 16

mating types: both a and alpha mating types, both contributing equal sized gametes so no male or female

mitosis of haploid cells: budding

Question 17

What is the asexual diploid part of the yeast life cycle?

Answer 17

mitosis of diploid part of life cycle

Question 18

What is the sexual part of the yeast life cycle?

Answer 18

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

Question 19

What are the advantages to the life cycle of yeast?

Answer 19

recessive allele phenotypes can be observed in the haploid stage

allele interactions can be examined in the diploid stage

Question 20

What is the ascus in the life cycle of yeast?

Answer 20

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

Question 21

What do the nucleic acid synthesis rules apply to?

Answer 21

DNA replication in a cell
RNA synthesis in a cell
DNA/RNA synthesis in the lab

Question 22

What are the nucleic acid synthesis rules?

Answer 22

1. made of NTPs –> RNA and dNTPs –> DNA
2. built in 5’–>3’, open 3’-OH is required in DNA/RNA pol
3. made using ssDNA template
4. complementary base pairing
5. anti-parallel

Question 23

What are centromeres on eukaryotic chromosomes?

Answer 23

attachment points for spindle

Question 24

What are telomeres on eukaryotic chromosomes?

Answer 24

repetitive regions at the tips of chromosomes

Question 25

What are the origins of replication on eukaryotic chromosomes?

Answer 25

where DNA synthesis begins 1000s of them

Question 26

What is the end replication problem?

Answer 26

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

Question 27

How does telomerase build telomeres?

Answer 27

protein (polymerase action) + RNA enzyme (tandem repeat that matches g-rich overhang) happens in early stages of life

Question 28

How are large amounts of DNA packed into a cell?

Answer 28

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

Question 29

What is euchromatin?

Answer 29

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

Question 30

What is heterochromatin?

Answer 30

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

Question 31

What is the structure of chromatin?

Answer 31

nucleosome: basic structure of chromatin linker DNA high-order chromatin structure: 30nm fiber, 300nm loops, 250nm wide fiber (listed from least to most dense)

Question 32

What are the steps to forming the different levels of organization in chromatin?

Answer 32

1. double helix 2. DNA wraps around histones (nucleosomes), beads on a string (basic unit chromatin) 3. coils up into 30 nm fiber 4. loops into 300 nm loop domains 5. folds up into 250 nm giber 6. finally coils into a metaphase chromosome

Question 33

What is a nucleosome?

Answer 33

the fundamental repeating unit of the chromatin

Question 34

What is a histone hetero-octamer?

Answer 34

2 each of: H2A, H2B, H3, and H4 these are the four genes involved in making the protein

Question 35

What is condensin?

Answer 35

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

Question 36

What is a karyotype?

Answer 36

physical description of an individuals or species chromosomes

Question 37

What does the human karyotype consist of?

Answer 37

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)

Question 38

What are metacentric chromosomes?

Answer 38

centromere right in middle

Question 39

What are telocentric chromosomes?

Answer 39

only lower arms

Question 40

What are acrocentric chromosomes?

Answer 40

very short arms on top

Question 41

How is a chromosome squash used to obtain images of chromosomes?

Answer 41

cheek or blood sample culture it --> put on slide --> squash it with coverslip

Question 42

How is a stain used to obtain images of chromosomes?

Answer 42

trypsin removes chromatin and allows the Giemsa stain to penetrate and show banding of chromosomes

Question 43

How do we get images of metaphase chromosomes?

Answer 43

karyotypes always describe metaphase chromosomes block metaphase checkpoint --> checks spindle block microtubes from forming spindle --> use a drug colchicine

Question 44

What is the nomenclature of karyotypes?

Answer 44

we can identify both the chromosome number and the regions of the chromosome by using standard nomenclature

Question 45

What is the nomenclature for chromosome number?

Answer 45

total number of chromosomes followed by number and type of sex chromosomes (XX or XY) humans: 46,XX or 46,XY

Question 46

What is the nomenclature for chromosomal number abnormalities?

Answer 46

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

Question 47

What are the arms on a chromosome?

Answer 47

p: petite arm q: long arm images are edited to have p arm always on top

Question 48

What is g-banding on a chromosome?

Answer 48

Giemsa dye: light and dark banding sometimes band number varies with the quality of the prep so scientists also use distinction of regions

Question 49

What is the nomenclature for g-banding?

Answer 49

gene is 18p11.2, which means chromosome 18 arm p region 1 band 1 sub-band 2