Download B2.3 Fact Sheet – Cell division, inheritance and speciation

B2.3 Fact Sheet – Cell division, inheritance and speciation
Cell division
1. What do chromosomes contain?
2. How many sets of chromosomes do body
cells contain?
3. How many sets of chromosomes do
gametes contain?
4. How many pairs of chromosomes are in
a human body cell?
5. Give the sex chromosomes of a female
6. Give the sex chromosomes of a male
7. Which type of cell division is used to
make new body cells?
8. Which type of cell division is used to
make gametes/ sex cells?
9. Which type of cell division produces
clones?
10. Which type of cell division produces
gametes?
11. Which type of cell division produces
offspring during asexual reproduction?
12. How many times does the cell divide in
Mitosis?
13. How many times does the cell divide in
Meiosis?
14. HT - Which two events occur when a
body cell divides by mitosis? (2)
15. When does mitosis occur? (2)
16. Cells in which human reproductive
organs divide to form gametes? (2)
17. HT - Which two events occur when a cell
divides by meiosis? (2)
18. Define ‘fertilisation’
19. How are babies formed from the single
body cell produced by fertilisation?
20. How does sexual reproduction lead to
variation in offspring?
Inheritance and genetic disorders
21. Define ‘gene’ (2)
22. Define ‘allele’
23. Define ‘dominant allele’
24. Define ‘recessive allele’
25. What is the genetic disorder polydactyly?
26. What is the genetic disorder cystic
fibrosis?
Genes/ genetic information
Two
One
23
XX
XY
Mitosis
Meiosis
Mitosis
Meiosis
Mitosis
Once
Twice




Copies of the genetic material are made
The cell divides once to form two genetically
identical body cells
During growth
To replace cells that are damaged or lost
Testes and Ovaries
 Copies of the genetic material are made
 The cell divides twice to form four gametes
When two gametes (sex cells) fuse
The body cell repeatedly divides by mitosis
When the gametes fuse, one of each pair of alleles
comes from each parent
 Small sections of chromosomes/ made of DNA
 They are instructions for characteristics
Different versions of the same gene
A person only needs one copy of this in order to
have the characteristic
A person needs two copies of this in order to have
the characteristic
Having extra fingers or toes
Disorder of cell membranes
27. Is the gene for polydactyly dominant or
recessive?
28. Is the gene for cystic fibrosis dominant or
recessive?
29. Which genetic disorder must be inherited
from both parents?
30. Which genetic disorder can be passed on
by only one parent?
31. What is the name for a person who has a
copy of an allele but doesn’t have the
associated characteristic?
32. How could a person develop cystic fibrosis
if neither of their parents have the
disorder?
33. SKILL – HT – draw a genetic diagram to
show how 2 carriers of a recessive disorder
could have a child with the disorder
(Alleles are A and a). Calculate the
probability of them having a child with the
disorder.(4)
Dominant
Recessive
Cystic fibrosis
Polydactyly
A carrier
If both parents are carriers (have just 1 cystic fibrosis
allele each)
1. Gametes in diagram correct
2. Genotypes of offspring correct
3. Child with disorder
CLEARLY identified
4. Correct probability
(here 25% or 0.25)
Gametes
Gametes
34. HT - Define ‘phenotype’
35. HT – Define ‘genotype’
36. Skill – HT – Describe this genotype (A,a)
37. Skill – HT – Describe this genotype (a,a)
38. Define ‘embryo screening’
39. 2 arguments FOR embryo screening (2)
40. 2 arguments AGAINST embryo screening
(2)
Mendel
41. Name the scientist who proposed how
characteristics are inherited
42. Why did this scientist propose the idea of
separately inherited factors? (4)
Describes the observable, physical characteristics an
organism has
Describes the combination of alleles an organism has
Heterozygous
Homozygous recessive
Is a process used to detect genetic disorders before
a baby is born
 Increase chances of having healthy child without
disorder (abort embryos with disorder)
 Prepare to provide better care after birth
 Healthy embryo may be miscarried as a result of
the procedure
 Chance of false positive and aborting healthy
embryo
Mendel

Noticed that parents characteristics were NOT
blended in the offspring
 Crossed smooth + wrinkly peas all smooth peas
 Crossed these  3:1 Smooth to wrinkly peas
 Realised that they can contain factors that code
for DIFFERENT characteristics to the ones that
they themselves have
43. Why was the importance of Mendel’s idea Other scientists then linked Mendel’s ‘inherited
(of separately inherited factors) not
factors’ with chromosomes and the actual
recognised until after his death?
mechanism for inheritance
Fossils and extinction
44. Define the term fossil
45. Describe four ways fossils can be made
46. List six things that can cause extinction
47. Why can’t scientists be certain about how
life began on Earth? (2)
48. Why are there few traces of early life on
Earth? (2)
49. What can we learn from fossils?
Speciation
50. Define ‘speciation’
51. What causes speciation to occur? (2)
52. HT – Describe all stages of speciation (5)
SKILL – you will need to be able to adapt
your description to the examples given in
exam questions
The remains of an organism from many years ago
 Hard parts which don’t decay e.g. bones and
shells
 Preserved parts from lack of decay e.g.
frozen
 Imprints such as footprints
 When parts of organism turn to stone
(petrification)
 Environmental change
 New predators
 New disease
 More successful competitors
 Catastrophic event e.g. volcanoes, asteroids
 The cyclical nature of speciation
There is a lack of…
 Valid and
 Reliable
…evidence
 Many early life forms were soft bodied and
so few traces remain
 Any traces there were have mainly been
destroyed by geological activity
How much or how little different organisms have
changed as life developed on Earth
How new species arise
 Isolation - 2 populations of a species become
separated
 Speciation - the populations become so different
that they can’t interbreed to produce fertile
offspring
 Isolation - 2 populations of a species become
separated
 There is genetic variation in each population
(each has a wide range of alleles)
 The conditions in each place are different
 Natural selection affects the populations
differently (in each population, advantageous
alleles are selected)
 Speciation – eventually populations become so
different that they can no longer interbreed to
produce fertile offspring