ch11 cell cycle and division

Question 1

chromatin fibres

Answer 1

-exist when cell is not dividing
-coil up tightly when cell division begins

Question 2

chromosome

Answer 2

-in duplicated stage when cell division begins (DNA molecules are replicated to make an extra copy)
-consists of two chromatids joined by centromere
-homologous chromosomes exist in pairs (e.g. humans have 23 pairs)
-each homologous pair are usually of same size and shape
-the paternal chromosome is from the father
-the maternal chromosome is from the mother

Question 3

chromatids

Answer 3

-chromatids are identical sister chromatids
-each chromatid contains one DNA molecule

Question 4

how to identify female and male through pairings of chromosomes?

Answer 4

• look at the 23rd pair of homologous chromosomes
  -male has an X and Y chromosome
  -female has two X chromosomes

Question 5

diploid cells

Answer 5

-contains two sets of homologous chromosomes (2n)
-most body cells (somatic cells) are diploids
-undergoes mitotic division

Question 6

haploid cells

Answer 6

-contains one set of homologous chromosomes (n)
-are present in sex cells (gametes)
-undergoes meiotic cell division
-haploid gametes fuse to form a zygote

Question 7

interphase (cell growth)

Answer 7

G1 stage
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S phase
-synthesis or replication of DNA
-synthesis of centromere

G2 phase
-cell growth to maximum size
-synthesis of organelles and proteins

Question 8

mitotic cell division

Answer 8

interphase
-DNA is replicated
-chromosomes are not visible

nuclear division (mitosis)
1. prophase
-chromosomes shorten and thicken, become visible, thread-like structures
-nuclear membrane breaks down
2. metaphase
-chromosomes line up at the equator
-spindle fibres attach to the chromosomes
3. anaphase
-spindle fibres contract
-sister chromatids separate and move to opposite poles
-cytoplasm divide
4. telophase
-new nuclear membrane forms around each group of chromosomes
-chromosomes uncoil to become chromatin again

cytoplasmic division (cytokinesis)
1. animal cells
-cell membrane constricts inwards until cell splits into two
2. plant cells
-cell plate made up of new cell membranes and cell walls is formed between two daughter nuclei
-cell plate grows outwards and divides the cell into two

Question 9

importance for mitotic cell division

Answer 9

growth
-provides new cells for growth of unicellular organisms

repair
-provides new cells for replacing worn-out cells or repairing damaged tissues

asexual reproduction
-produce offspring by mitotic division (e.g. amoeba, potato)

Question 10

meiotic cell division

Answer 10

interphase
-replication of DNA
-chromosomes are not visible

first nuclear division (meiosis I)
1. prophase I
-chromosomes shorten and thickens, become visible, thread-like structures
-homologous chromosomes pair up
-crossing over may occur

2.metaphase I
-homologous pairs line up at the equator
-spindle fibres attach to the chromosomes

3.anaphase I
-spindle fibres contract
-two members of each homologous pair separate and move to opposite poles
-cytoplasm starts to divide

4.telophase I
-new nuclear membranes form around each group of chromosomes

cytoplasmic division (cytokinesis)
-two haploid daughter cells with chromosomes in duplicated stage

second nuclear division (meiosis II)
1.prophase II
-nuclear membrane is broken down again

2. metaphase II
   -chromosomes line up at the equator
   -new spindle fibres attach to chromosomes

3.anaphase II
-spindle fibres contract
-sister chromatids separate and move to opposite poles
-cytoplasm starts to divide

4.telophase II
-new nuclear membrane form around each group of chromosomes
-chromosomes uncoil and become chromatin

cytoplasmic division (cytokinesis)
-four haploid daughter cells that are genetically different from each other

Question 11

down syndrome

Answer 11

-extra chromosome 21, 47 chromosomes in total in each somatic cell
-physical signs: flattened face, short neck, small ears
-caused by nondisjunction

Question 12

importance of meiotic cell division

Answer 12

producing haploid gametes
-meiosis produces haploid gametes for sexual reproduction
-diploid number of chromosomes is restored
-allows species to preserve a constant number of chromosomes to the next generation

genetic variations in gametes
-genetic variations are caused by independent assortment of chromosomes and crossing over
-increase the chance for the species to survive when environmental conditions change

Question 13

independent assortment (random segregation)

Answer 13

-homologous pairs line up randomly (metaphase I)
-each homologous pair separate independently
-produces various genetic combinations

Question 14

crossing over

Answer 14

-exchange of corresponding segments of a maternal chromatid and paternal chromatid
-produces new genetic combinations