cell division 3.28, 3.29, 3.30, 3.31, 3.32, 3.33, 3.34, 3.36B, 3.37B Flashcards
how many chromosomes does the human body have?
23 pair of homologous chromsomes that contain the genes
23 chromosomes from the mothers egg cell
23 chromosomes from the fathers sperm cell
what type of daughter cells does mitosis produce?
- produces genetically identical cells
- produces diploid cells (one pair of each chromosome in each nucleus)
- human diploid cells have 23 pairs of chromosomes 46 in total
what is mitosis used for?
growth, repair and asexual reproduction
what type of cells does meiosis produce?
- produces haploid gametes (sperm, egg and pollen)
- not genetically identical
- human haploid cells have 23 chromosomes in total (unpaired)
- halves the number of chromosomes
what is meiosis used for?
only used to produce gametes for sexual reproduction
what is the consequence of meiosis?
every gamete produced is genetically different and carries different alleles from every other gamete
it is random which sperm/pollen grain fertilises an egg, therefore variation in offspring is produces by:
- genetic variation in gamete cells produced by meiosis cells
- random fertillisation of ova by male gamates
how many cells does mitosis produce?
produces two cells
how many cells does meiosis produce?
produces four cells
how many cell divisions does mitosis involve?
involved one division
how many cell divisions does meiosis involve?
involves two cell divisions
what is the process of cell division with mitosis?
- the DNA replicates to form two copies of each chromosome, these copies (chromatids) are joined together at a single point (the centromere)
- the nuclear membrane breaks down and the chromosomes line up across the centre of the cell attached to spindle fibres
- the chromatids are pulled apart and move to opposite sides of the cell
- the cytoplasm and cell membrane divide to form two identical cells
what is the process of cell division with meiosis?
- the DNA replicates to form two copies of each chromosome, these copies (chromatids) are joined together at a single point (the centromere)
- the nuclear membrane breaks down, the homologous pairs of chromosomes join together
- the homologous pairs of chromosomes exchange sections of DNA and they then attach to the spindle fibres in pairs at the centre of the cell
- the homologous pairs of chromosomes are pulled apart and move to opposite ends of the cell, the cell divides
- the chromosomes line up along the centre of the cell attached to the spindle fibres, and the chromatids separate and move to opposite ends of the cell, each cell divides again
variation in a particular characteristic can be…
genetic, environmental or a combination of both
what are the two types of variation?
continuous - where there is a smooth range of measurements/data
discontinuous - where there is distinct categories with no values in between
what is a mutation?
a change in the sequence of bases in dna
- this can be due to a replacement of a single base pair with a different pair or the addition or deletion one or more base pairs
are mutations common or rare?
rare in eukaryotes as our cells can detect and correct many mistakes in our dna sequence
are chromosomal mutations harmful?
yes as they result in an over or under production of proteins
what effect does a change in the dna sequence have?
no effect, but can less often be either positive or negative
how is a mutation inherited?
if mutation occurs during meiosis in gamete formation it will affect all the cells in the individual which develops from the gamete
how is a mutation not inherited?
if the mutation occurs in a body cell it will only affect those cells produced by mitosis from the affected cell, mutations in the body cells give rise to cancers of the cells affected
what are mutagens?
chemicals which cause more frequent mutations
examples of mutagens:
- ionising radiations (gamma, X-rays and uv)
- some chemicals like tobacco
