3.2 Mitosis And Meiosis Flashcards
Describe the cell cycle.
- INTERPHASE (G1, S, G2)
- G1 - all cell components except chromosomes replicate
- S all chromosomes (23 pairs) replicate
- G2 cell double checks for errors making any repairs - DIVISION (M)
- mitosis
What is G0?
Cell exists here in a quiescent state (not dividing nor preparing)
What is a telomere and its function?
- Repeated sequences (TTAGGG) at ends of chromatids
- Protect from degradation and fusion with other chromosomes
- Shorted with replication and causes senescence
Complete the sentence:
One chromosome is made of _______________________
A. One DNA molecule
B. Two DNA molecules
C. One or Two DNA molecules
C. One or Two DNA molecules
What are sister chromatids? (2)
- Limbs of X shaped chromosomes
2. 2 identical DNA molecules with same alleles
How would you identify the p and q arms?
P arm is short (usually top one diagrammatically), q arm is longer (usually lower one diagrammatically)
How are chromosomes grouped?
- According to shape and size
- A-G
- X is a C group and Y is a G group
What are homologous chromosomes?
Pair of chromosomes
Have same genes
May have different alleles
Define diploid and haploid.
Diploid - full 46 chromosomes
Haploid - 23 chromosomes
What is mitosis and its stages?
- Cell division for somatic cells producing two identical daughter cells
- Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis
What happens during prophase?
- Nuclear membrane and nucleolus disappear
2. Chromosomes condense and become visible
What happens during Prometaphase?
- Microtubule spindle fibres move to opposite ends of the cell
- Kinetophores connect to chromosomes, spindle to kinetophores
What happens during metaphase?
- 46 chromosomes randomly line up in middle forming metaphase plate
What happens during anaphase?
- Centromeres divide and spindles pull each chromosome apart
- Chromatids (now called chromosomes) go to each pole of the cell
What happens during telophase?
- Spindles disappear, nuclear membranes reappear
2. Cleavage furrow forms
What happens during cytokinesis?
- Cytoplasm divides
2. Birth of two daughter cells
Why cant we see the chromosomes during interphase?
- Not condensed
2. In chromatin - hetero and eu - form
What is the function of meiosis? (4)
- One germ line diploid cell (46 chromosomes replicated (X shaped)) to 4 haploid cells (23 chromosomes (I shaped))
- Maintain constant chromosome number from generation to generation
- Genetic diversity by random assortment of chromosomes
- Genetic diversity by crossing over of genetic material (chiasma)
How does meiosis I happen?
- Prophase I
- nuclear membrane and nucleolus disappear
- chromosomes condense and become visible
- homologous pairs find each other and Chiasmas occur (crossing over) - Metaphase I
- homologous pairs lines up on metaphase plate
- random assortment - Anaphase I
- microtubule spindle fibres pull one chromosomes from each pair to each pole (23 chromosomes replicated (X shaped) ) - Telophase I
- spindles disappear, nuclear membrane reappears
- cleavage furrow
- 2 daughter cells with 23 X shaped chromosomes
What happens during meiosis II?
We start with 2 daughter cells with 23 X shaped chromosomes from meiosis I
- Prophase II
- nuclear membrane and nucleolus disappear - Metaphase II
- 23 chromosomes (X shaped) line up on metaphase plate - Anaphase II
- centromeres divide and spindles pull each chromosome apart
- go to each pole of cell - Telophase II
- spindles disappear, nuclear membrane reappears
- cleavage furrow
- 4 haploid daughter cells :)
How does a sperm cell develop?
Spermatogenesis
- Spermatogonium, mitosis, more spermatogonium. OR
Spermatogonium, mitosis, 1 spermatogonium, diploid primary spermatocyte - Meiosis I forms secondary spermatocyte
- Meiosis II forms 4 spermatids
- Maturation forms 4 mature sperm cells
How does an egg cell develop?
Oogenesis - 1 big egg produced from one diploid cell!
- Oogonium goes through mitosis and forms more oogonium (before birth) but after birth forms primary oocyte
- Primary oocyte goes through meiosis I and pauses at prophase I
- Monthly, 1 primary oocyte finishes meiosis I becoming a secondary oocyte (other one from oogonium becomes a polar body)
- Release from ovary and fertilisation
- Meiosis II produces one big egg cell and one small polar body which stays attached to egg cell
- One daughter cell gets all of cytoplasm , containing all nutrients forming zygote
What is a polar body?
Formed from oogenesis and acts as a garbage can from chromosomes that we dont want (as one oogonium diploid 2n only forms one haploid egg cell!)
What are the effects is meiosis doesn’t occur properly?
- A third of all identified miscarriages are due to this
- Infertility
- Leading cause of mental retardation
What is missegregation/non-disjunction?
- In metaphase, all chromosomes line up correctly
- In anaphase, both copies of X shaped DNA that usually splits into two I shaped, go to one pole
- Results in one pole having one copy too many and other pole having one copy too less
Name two ways chromosome analysis can occur and explain briefly
- Metaphase spread - chromosomes spread on glass plate. Different stains can be used to see every chromosome.
- Karyotyping - number and visual appearance of chromosomes can be seen and chromosome number, sex, structural changes can all be identified
How would you write the karyotype of i) a normal female and ii) a male with trisomy 21
46,XX
47,XY+21
What are the two types of non-disjunction you can have?
Mitotic and meiotic
What is aneuploidy?
Presence of abnormal number of chromosomes in a cell resulting from mitotic nondisjunction
What is mosaicism and how does it happen?
Presence of 2 or more cell lines in an individual (throughout body or throughout a tissue)
Depends on when non-disjunction occurs (first post-zygotic division (non-mosaic!) or through later mitotic divisions (mosaic!)
What is anaphase lag?
Different to non-disjunction
May lose one chromatid due to delayed movement/not attaching to spindle
What stage does crossing over occur?
Prophase I
What stage does random assortment occur?
Metaphase I
What is i) monosomy and ii) trisomy?
Monosomy is presence of only one chromosome
Trisomy is presence of three chromosomes (Extra one appeared from non-disjunction)
What are the four chromosome structures due to centromere placement?
Metacentric, submetacentric, Acrocentric and telocentric
What happens at a cell cycle checkpoint to allow the cycle to continue?
Checkpoint proteins phosphorylated
