B3: Cell division + sex determination Flashcards
what happens during interphase
cell grows
chromosomes in nucleus replicated
cell respires to provide energy for respiration
why is replication important
allows for full set of chromosomes
identical to parent cell
what does a chromosome look like after replicaiton
two sister chromatids
held together by centromere
roles of mitosis
allows organisms to increase in size by increasing total no. of cells
allows worn out + dead cells to be repaired + replaced
allows reproduction by asexual reproduction
what does the cell do when preparing for interphase
cell cycle pauses
to check cell is healthy + DNA has been copied correctly
what happens if errors detected in cell
cell destroyed
what happens if errors not detected
cell cycle contines + divided by mitosis
may lead to defective cells
how does cancer develop
group of defective cells that divide uncontrollably
forming a tumour
in fertilisation, the gametes fuse to form…
a zygote
where and how are sperm cells produced
testes
meiosis
where and how are ova produced
ovaries
meiosis
importance of meiosis
- meisosis halves no. of chromosomes
- gametes produced are genetically different from each other + parent cell
= produces genetic variation
use of meisosis
gamete production during sexual reproduction
what takes place during asexual reporduction
one parent needed
no production / fusion of gametes
offspring genetically identical to parent
binary fission
- bacterial cell reproduces by binary fission- produces copy of loop of chromosomal DNA in cytoplasm
- cell divided into two, each daughter cell gets copy of loop
- not always identical as DNA can be mutated= daughter cells get diff chromosomal DNA
what happens in sexual reporducion
- two parents involved
- each parent produces specialised cells - gametes
- gametes produced by meiosis
- gametes fuse at fertilisation
- offspring genetically different
why are offspring genetically different in sexual reproduction`
- to their parents : receive half of their genetic information
from each parent in the gametes
-to each other : the gametes produced by meiosis are genetically different from each other
it is completely random which of the gametes from each parent will then fuse at fertilisation to form the zygote.
Importance of producing genetically different offspring
- so genetic variation is maintained within a species.
- Genetic variation is essential for natural selection.
- Natural selection enables populations of organisms to adapt to changes in the environment. It ensures the successful continuation of a species over time.
- Genetic variation within a species also helps to reduce the frequency with which recessive inherited conditions occur.
females have… chromosomes
XX
males have….chromosomes
XY
why cant a male be produced with the x chromosome
Y chromosome contains key genes
needed to intiate male secual development
