Cell Division Flashcards
How many chromosomes are there in human cells
Diploid number is 46
Haploid number is 23
When does mitosis occur
During growth, repair, cloning and asexual reproduction
Describe the stages of mitosis
Division of a diploid cell
Prophase: The DNA in chromosomes and their copies condenses to become more visible. The nuclear membrane breaks
Metaphase: Chromosomes and their copies line up in the middle of the cell
Anaphase: Chromosomes and their copies are pulled to different ends of the cell.
Telophase: New membranes form around the chromosomes at each end of the cell.
Cytokinesis: The cell membrane pinches in and eventually divides into two daughter cells.
How plants reproduce asexually
Runners- naturally: stems growing sideways with plantlets on them
Cuttings- artificial: A branch from the parent plant is cut off and the stem is planted in damp compost. Plant hormones are often used to encourage new roots to develop. New roots develop and a new plant is produced
What does mitosis produce
s two cells which contain identical sets of chromosomes
What does meiosis produce
Produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes
Describe the stages of meiosis
Parent cells Chromosomes make identical copies of themselves Similar chromosomes pair up Sections of DNA get swapped Pairs of chromosomes divide Chromosomes divide
Random fertilisation
The four gametes produced in meiosis are genetically different.
Genetic variation of offspring
Independent assortment and the random nature of fertilisation lead to variation in living organisms – no two organisms are the same (apart from identical twins).
What is cell differentiation
Process by which undifferentiated cells become specialised to carry out a specific function
What is a stem cell
A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.
Advantages of stem cells in medicine
Stem cells from the embryo aren’t rejected by the patient’s body so they are perfect for medical treatment- the cells are genetically identical to the parent.
These transplants also do not require the death of another person, whilst customary transplants do today.
Stem cells can be taken from embryos that have stopped developing
Disadvantages of stem cells in medicine
Transfer of viral infections
Embryonic stem cells are capable of continued division and may develop into cancerous cells, causing tumors Involves the creation and destruction of human embryos
