Chapter 3

Question 1

Chromosome

Answer 1

• an arrangement of DNA with genes at specific regions (loci)

some determine sex (sex chromosomes)

some don’t (autosomes)

Question 2

Ploidy

Answer 2

the number of copies of each chromosome in any given cell

diploid (2n) cells have two copies of each chromosome
(ex. somatic cells)
- two copies of genetic material

haploid (n) cells have one copy of each chromosome
(ex. germ cells)

Question 3

Homologous chromosomes

Answer 3

contain the same genes in the same order

Question 4

Diploid vs haploid lifecycles

Answer 4

humans mostly diploid
- except meiosis to fertilization

fungi and unicellular eukaryotes mostly haploid
- except nuclear fusion to meiosis
- mature, ecologically form is haploid

Question 5

Mitosis vs meiosis and ploidy

Answer 5

mitosis
- produces diploid cells
- genetically identical chromosomes
- how somatic cells reproduce

meiosis
- produces haploid cells
- not genetically identical
- how gametes are produced (sperm and eggs)

Question 6

Cell division issues

Answer 6

too much
= cancer, morphological abnormalities, and death

too little
= inappropriate development and growth

Question 7

Three stages of mitosis

Answer 7

M-phase:
- cell division

Interphase:
- 3 parts

G0:
- division arrested
- specialized cells eventually die

Question 8

3 parts of interphase

Answer 8

G1
- high gene expression to prepare for replication

S phase
- DNA replication occurs

G2
- preparation for cell division

chromosomes duplicated

Question 9

Parts of M phase

Answer 9

Prophase
- chromo condense

Prometaphase
- nuclear envelope breaks down
- microtubules attach

Metaphase
- chromo align at plate

Anaphase
- sister chromatids separate

Telophase
- new nuclear membrane forms

Cytokinesis
- daughter cells separate

Question 10

Nuclear contents of a cell during mitosis

Answer 10

End of…

G1
- 46 somes
- 46 tids

S
- 46 somes
- 92 tids

Mitosis
- 46 somes
- 46 tids

Question 11

Cell cycle checkpoints

Answer 11

• failure = death
• mutations affecting cycle controls = growth abnormalities
• loss of control = cancer

checkpoints at the end of the phase

Metaphase checkpoint
- chromos attached to mitotic spindle

G1 checkpoint
- cell size, nutrients available, growth factor signals

S phase checkpoint
- DNA replication complete

G2 checkpoint
- cell size and complete chromo replication

Question 12

Meiosis

Answer 12

• produces gametes for sexual reproduction
• produces haploid cells
• two stages = meiosis I and meiosis II
• no DNA replication between phases

Question 13

Steps of meiosis

Answer 13

diploid precursor cell
heterozygous (ex. Gg)

chromatids duplicated into homologous chromosomes during interphase

first meiosis separates homologous chromos into separate cells

second meiosis separates each sister chromatid into separate cells
= gametes

Question 14

Meiosis 1 (3 main events)

Answer 14

1. homologous chromosomes pair
2. crossing over / recombination
3. duplicated homologous chromosomes separated into two daughter cells

Question 15

Steps of meiosis 1

Answer 15

Prophase 1
- homologous chromosomes pair and recombine in tetrads

Metaphase 1
- homologous pairs align

Anaphase 1
- chromosomes separate
- sisters still attached

Telophase 1
- nuc membrane forms and cleavage furrow

Cytokinesis
- cells separate

Question 16

Meiosis 2 (1 main event)

Answer 16

separation of sister chromatids into separate daughter cells

results in 4 distinct haploid daughter cells

Question 17

Recombination

Answer 17

occurs during prophase 1 in meiosis 1

before homologs separate

mediated by the synaptonemal complex that forms between homologous chromosomes

Question 18

Nuclear contents of a cell during meiosis

Answer 18

G1 and S same as mitosis

G1
- 46 somes
- 46 tids

S
- 46 somes
- 92 tids

Meiosis 1
- 23 somes
- 46 tids

Meiosis 2
- 23 somes
- 23 tids

Question 19

Allele segregation

Idk bout this

Answer 19

during recombination (prophase 1) and when homologs separate (metaphase 1)

metaphase 1 arrangement dictates independent assortment of multiple genes

Question 20

Oogenesis and spermatogenesis

Answer 20

produced through meiosis

Oogenesis
- produces 1 egg cell per division and 1-3 polar bodies

Spermatogenesis
- produces 4 sperms per cell division

Question 21

Primary oocytes

Answer 21

established in the mother 20 weeks after conception - during embryonic development

7 million present
1-2 million by birth
60 000 - 80 000 by puberty

500 mature oocytes produced during a woman’s life

Question 22

Oogenesis

Answer 22

in utero:
2n oogonium
2n primary oocyte

after puberty:
n secondary oocyte (ovulated) + polar body

n meiosis to completion + polar body

Question 23

To determine total DNA content of daughter cells

Answer 23

compare number of chromatids

Question 24

Drosophila experiment results

Answer 24

genes are carried on chromosomes

• Thomas Hunt Morgan rediscovered Mendel’s laws
• also contributed to the understanding of the chromosomal basis of sex determination

looked at wild type (usually normal flies) compared to mutated flies

Question 25

X-linked inheritance discovery

Answer 25

- discovered by Nettie Stevens - looked at chromosomal differences in male and female beetles 2n female cells: 20 large chromos 2n male cells: 19 large, 1 small small = y chromo

Question 26

White-eyed mutant flies

Answer 26

discovered by morgan recessive to red eyes sex linked on the X chromosome

Question 27

X-linked recessive inheritance

Answer 27

traits will be more common in males inherit the condition directly from carrier mothers 3:1 dom:rec but the 1 will be the male ex. colourblindness, hemophilia A

Question 28

Hemizygous

Answer 28

having only one copy of a gene or locus in a diploid organism ex. males are hemizygous for the X chromosome

Question 29

Sex determination due to chromosomes different animals

Answer 29

Humans/mammals - Y determines male Platypus - 5 pairs of sex chromosomes 5XX = female, 5XY = male Birds/reptiles/butterflies/moths - ZW system ZW = female, ZZ = male

Question 30

Drosophila sex determination

Answer 30

- Y no effect - X:A ratio system - ratio of X to autosomes determines sex X expresses sisterless autosomes express deadpan when sisterless dimerize (high concentrations), female flies produced when deadpan dimerizes with sisterless, males produced XX = females X = male

Question 30

Y chromosome

Answer 30

contains gene called sex determining region of Y (SRY) males - XY - XXY, XYY, XYYY females - XX - XO, XXX, XXXX

Question 30

Z/W sex determination

Answer 30

opposite of humans females - ZW males - ZZ

Question 31

X-linked dominant inheritance

Answer 31

1. hetero females transmit dom to half their offspring 2. daughters of dominant males will pas the trait directly to their daughters

Question 32

Congenital hypertrichosis (CGH)

Answer 32

rare x-linked dominant condition large increase in number of hair follicles on the body

Question 33

Dosage of X-linked genes too high

Answer 33

females express double what males do undergo dosage compensation in mammals, one X randomly inactivated in each somatic cell

Question 34

X-inactivation in female placental mammals

Answer 34

occurs in early embryonic development inactivates either the maternal or paternal X in females random cells are therefore mosaics; one expresses paternal while the other expresses maternal

Question 35

Mosaicism - humans and cats

Answer 35

- visible in women with x-linked skin conditions "Lines of Blaschko" calico cats one allele black, one for orange each has unique patch patterns