Cell Division and sex determination Flashcards
(11 cards)
When does the stage Interphase take place as part of the cell cycle? What happens to the cell at this stage?
- Interphase is the first stage before mitosis and meiosis
- This is the stage the cell is in for most of the time
- The cell grows; subcellular structures divide
- DNA replicates(chromosomes duplicate)
- Cell respires to provide energy for mitosis
How does a chromosome change when it is replicated?
BEFORE REPLICATION:
- 1 chromosome
- the chromosome contains 1 DNA molecule
- Centromere attach to the middle of this chromosome
AFTER REPLICATION:
- Chromosome appears in it’s “X shape”
- The chromosome now consists of 2 identical sister chromatids attached at the centre by the centromere
Describe what happens during mitosis
AFTER THE CHROMOSOMES DUPLICATE AS A RESULT OF INTERPHASE:
- Nucleus disappears
- Chromosomes line up at the equator
- Spindle fibres pull the 2 identical arms of each chromosome apart and towards opposite poles of the cell
- A new nucleus forms around each set of chromosomes
- Cytoplasm divides forming 2 IDENTICAL daughter cells
What are the roles of mitosis?
- Allows organisms to grow in size by increasing their total number of cells
- Allows worn-out dead cells in a tissue to be repaired and replaced
- Allows some species to reproduce by asexual reproduction
How can mitosis lead to the development of cancer?
- As a cell prepares for mitosis during interphase the cell cycle pauses temporarily to check the cell is healthy- if the DNA has copied correctly
- If errors are detected like a mutation in the DNA that cannot be repaired, the cell is destroyed
- However if the cell is not destroyed, the cell cycle will continue- the cell will divide by mitosis
- This may lead to a group of cells are defective and divide uncontrollably, which can form a tumour
- Thus developing cancer
Describe what happens during meiosis
AFTER THE CHROMOSOMES DUPLICATE AS A RESULT OF INTERPHASE:
- Homologous chromosomes pair up and each pair lines up at the equator
- Each chromosome pair is separated during the first division
- Now there are 2 cells with either the maternally or paternally inherited chromosome
- Again, all chromosomes line up at the equator
- Now the 2 arms of the chromosomes are pulled apart during the second division
- In total 4 new daughter cells are formed, each of which have half the number of chromosomes as the original AND they are all genetically different
What are the roles of meiosis?
- Reduces (halves) the chromosome number- this is very important; prevents the chromosome number doubling when fertilisation takes place
- Produces gametes that are genetically different; helps to produce genetic variation in offspring; aids survival
What is meant by Sexual reproduction?
What are the characteristics of a cell undergoing sexual reproduction?
Reproduction that uses the process MEIOSIS:
- Requires 2 parents
- Parent cell undergoes 2 divisions
- 4 cells made
- At the end the cells are haploid (contain half the no. of chromosomes as the parent cell) [23 chromosomes]
- There is variation in the cells
- The new cells are NOT CLONES
- Increases survival; allows nature to “select” advantageous characteristics- evolution
- Slow process
- PURPOSE: produce gametes
- Occurs in the sex organs
What is meant by Asexual reproduction?
What are the characteristics of a cell undergoing asexual reproduction?
Reproduction that uses the process MITOSIS:
- Only 1 parent cell
- Parent cell undergoes division only once
- 2 cells made
- At the end the cells are diploid (contain the same no. of chromosomes as the parent cell) [46 chromosomes]
- There is no variation in the new cells
- The new cells are CLONES
- Does NOT increase/ aid survival; if a new disease/ environmental change affects 1 individual- it will affected the whole population
- Fast process
- PURPOSE: Growth + repair
- Occurs in every cell for humans, except sex organs & occurs in bacterial cells
What is fertilisation
The process by which the gametes from 2 parent cells fuse together after meiosis
How is the sex of an individual determined in humans (most animal species)?
- Of the 23 chromosomes in human cells, or pair are referred to as sex chromosomes
- The sex of an individual is determined by the combination of these sex chromosomes
- Each human SPERM contains 23 chromosomes, one of which is a sex chromosomes: X OR Y
- Each human OVUM contains 23 chromosomes, one of which is ALWAYS AN X
- At fertilisation, it is the sperm that determines the sex of the resulting zygote
- When a Y chromosome is delivered to the egg by the sperm the zygote will develop into a male
- When an X chromosome is delivered to the egg by the sperm the zygote will develop into a female
