Meiosis and sexual reproduction Flashcards
(93 cards)
1
Q
What does asexual reproduction leave population vulnerable to
A
changes in the environment
2
Q
Whats the difference between mitosis and meiosis in term of daughter cells
A
mitosis:
daughter cells re identical to parent cells
meiosis:
daughter cells are not identical to parent cells
3
Q
Give examples of organisms in which sexual reproduction is the main type of reprodution
A
animals and flowering plants
4
Q
What is sexual production
A
The production of a new individual resulting from the joining of two specialised cells known as gametes
5
Q
Whats a great advantage if sexual reproduction
A
Increases genetic variations
6
Q
What is a diploid cells (2n)
A
A cell containing two full sets of chromosomes
7
Q
What are haploid cells
A
A cell containing one complete set of chromosomes
8
Q
When does sexual reproduction occur
What is this process called
A
When two haploid nuclei fuse to form a new diploid cell known as a zygote
Fertilisation
9
Q
Where are gametes formed
A
In special sex organs
10
Q
What are gonads
A
sex organs in animals
11
Q
What is polypidy
A
When a cell or organism has more than two sets of chromosomes
12
Q
In plants what is the following:
1) anthers
2) Ovaries
A
a) Anthers-male sex organs
b) Ovaries-female sex organs
13
Q
Where are the male gametes in plants formed
A
In pollen
14
Q
Where are the female gametes in plants formed
A
Ovules
15
Q
What is the male gonad in animals
what does it produce
A
Testes
sperm
16
Q
What is the female gonad in animals
what does it produce
A
Ovaries
Ova/eggs
17
Q
Why does the number of chromosomes in both daughter cells need to be halved in meiosis
A
To give the necessary haploid nuclei
18
Q
What is meiosis
A
A reduction division and occurs only in sex organs
19
Q
What special cells does meiosis in flowering plants form for:
Males
Females
A
Microspores
Megaspores
20
Q
In meiosis what does the two nuclear divisions cause
A
It gives rise to four haploid daughter cells, each with its own unique combination of genetic material
21
Q
What are the differences between the stages of meiosis and mitosis
A
1) The two chromosomes of each pair (homologous chromosomes) stay close together
2) Crossing over or recombination takes place
3) Centromere does not split in the first division, so pairs of chromatid move to opposite sides of pole
4) Cytokinesis takes place giving 4 haploid daughter cells
5) Daughter cells later develop into gametes
22
Q
What are chromosome mutations
A
When during meiosis, parts of the chromosomes break off and become reattached to the wrong place
23
Q
Whats one of the most common forms of chromosome mutations
When does this type of chromosomal mutation take place
A
Translocation
When one pair of homologous chromosome breaks off and reattaches to one of a completely different pair of chromosomes
24
Q
Are all translocations bad/unhealthy
A
No if its balanced its healthy but if its unbalanced it causes huge changes within the phenotype of an individual
25
In humans what should each gamete carry
Contain 23 chromosomes, including ONE SEX CELL
26
What is non-disjunction
The process that occurs when members of a pair of chromosomes fail to seperate during the reduction division of meiosis, resulting in one gamete with two copies of a chromosome and one gamete with no copies if that chromosome
27
What happens if one of these abnormal gametes joins with a normal gamete and is fertilised
The individual who results will either have monosomy with only one member of the homologous pairs present from the normal gamete or polysomy with three or more rather than two chromosome of a particular type
28
What is meant by Aneuploidy
When a cell contains too few or too many chromosomes
29
What is an example of:
a) Polysomy disease
b) monosomy disease
a) down syndrome
| b) Turners syndrome
30
What are people that have down syndrome born with
They are born with trisomy of chromosome 21
31
What does the extra chromosome in down syndrome affect
It affects both mental and physical developement
32
What problems do kids born with down syndrome suffer from
Heart abnormalities, learning difficulties , lack of muscle tone and visual problems
33
What genotype does turners syndrome suffers have
XO
| The affected person is female but does not have any sex cells and is infertile. They also cannot undergo puberty
34
What is Kleinfelter's syndrome
When you have the genotype XXY
| small testes and can develope breast. May also be infertile
35
What are primordial germ cells
Special cells in the gonads that divide, grow, divide again and then differentiate
36
What is Gametogenesis
The formation of the ganetes by meiosis in the swx organs
37
What is spermatogenesis
Formation of spermatozoa
38
What does each primordial germ cell in the testes result in
Large number of spermatozoa
39
What are the number of primordial germ cells in the testes producing millions of spermatozoa on regular basis
1) diploid primodal germ divides by mitosis several times to form diploid spermatogonia
2) spermatogonia then grow without further division until they're big enough to be called primary spermatocytes
3) spermatocytes undergoes meiosis.First meiotic division forms two haploid cells known as secondary spermatocytes
4) Second meiotic division results in 4 haploid cells called spermatids
5) Spermatids then differentiate in the tubules of the testes to form spermatozoa, the active gametes capable of fertilising an ovum
40
What is oogenesis
The formation of ova
41
Describe the process of oogenesis
1) The diploid primodial germ cell divides several times by mitosis to form diploid oogonia
2) Most oogonia degenerate but only one continues to grow
3) The large cell is known as the primary oocyte
4) The oocyte undergoes meiosis
5) The first meiotic division results in un equal size and the larger size one is known as the secondary oocyte
6) The smaller sized one is known as the first polar body
7) oocytes at this stage do not divide until after ovulation
42
What do we call ova in the ovaries
secondary oocytes
43
When is the second meiotic division completed
After fertilisation occurs
44
What does the secondary oocytes divide to form
The haploid ovum and another polar body
45
What does the first polar body divide to form
Two more polar bodies
46
Whats the one function of the polar bodies
To receive the chromosomes in the meiotic divisions
47
Charecteritics of male gametes (spermozoa)
.50um long
.must remain in suspension in the semen so they can be transported through the female reproductive tract
.penetrate the protective barrier around the ovum and deliever the male haploid genome safely
48
Charecteritics of female gametes (Ova)
.0.1nm across
.Contaoin food for development if embryo
.large food stores
49
why is the formation of gametes in flowering plants more complex
Because plants have two phases to their life cycle
50
What are the two phases to the plant's life cycle
| Explain what each one means
The sporophyte generation
.diploid
.produces spores by meiosis
The gametophyte generation
.Haploid
.gives rise to the gametes in mitosis
51
What is the main body of the plant that we see
the diploid sporophyte
52
What are the haploid gametophytes reduced to
Parts of the contents of the anther and the ovary
53
What does each anther contain
Four pollen sacs where pollen grain develops
54
What is there in each pollen sac
| How do they divide
Large numbers of microspore mother cells
| They're diploid and divide via meiosis to form haploid microspores
55
What are the gametes formed from in plants
| What do they contain
From the microspores by mitosis
| Two haploid nuclei, tube nucleus, and the generative nucleus
56
What's the function of the tube nucleus
Producing a pollen tube that penetrates through stigma, style, and ovary and into the ovule
57
How are new individuals formed in plants
the generative nucleus fuses with the nucleus of the ovule
58
What does meiosis result in plants
The formation of a relatively small number of ova contained within ovules inside the ovary
59
Where is the ovule attached
To the wall of the ovary by a pad of a special tissue called the placenta
60
What is the nucellus
A complex structure of integuments that form around tissues
61
Why do diploid megaspores mother cells divide by meiosis
To give rise to four haploid megaspores
62
Wat di the megaspore undergo
| What does this result in
Three mitotic divisions
| Results in an embryo sac containing an egg cell, two polar nuclei, and various other small cells
63
What is pollination
The transfer of pollen from the anther to the stigma, often from one flower to another
64
What are the two main categories in which animals make sure gametes meet
1) External fertilisation
| 2) Internal fertilisation
65
What is External fertilisation
What species is this common in
The process of fertilisation in which the female and male gametes are released outside of the parental bodies to meet and fuse in the environment
aquatic species
66
What is internal fertilisation
The fertilisation of the female gamete by he makes gamete takes place inside the body of the mother
67
Which lasts longer the:
| sperm or ovum
Sperm lasts much longer
68
What happens as the sperm moves through the female reproductive tract
The acrosome region matures so it is able to release enzymes and penetrate the ovum
69
What is the ovum released at ovulation
| What is it surrounded by
secondary oocyte with one polar body
| The protective gel-like layer known as zona pellucida
70
when is the acrosome reaction triggered
As soon as the sperm goes head to head with the ovum
71
what do the enzymes release from the acrosomes digest
it digests the follicle cell and the zona pellucida
72
What happens when the protective layer is weakened by many sperm cells
Eventually, one sperm cell will wiggle its way through and touch the surface membrane of the oocyte
73
What happens when the sperm touches the surface membrane of the oocyte
The oocytes complete its second meiotic division providing a haploid egg nucleus to fuse with the haploid male nucleus
74
What would happen if more than one sperm enters the egg
It will be fertilised bu too many sperms (polyspermy)and would produce a nucleus containing too many sets of chromosomes
75
What prevents more than one sperm entering the egg
How long does this last
The ion channels in the cell membrane of the ovum open and close so that the inside of the cell, instead of being electrically negative with respect to the outside, becomes positive
Until the tough fertilisation membrane forms around the fertilised ovum
76
What part of the sperm fertilises with the egg
The head
77
What happens once the head of the sperm is inside the ovum
It absorbs water and swells, releasing its chromosomes to fuse with those of the ovum and forms a diploid zygote
78
Where is the male gamete contained within plants
The pollen grain
79
where is the female gamete embedded
Deep in the tissue of the ovary
80
How does the fertilisation in plants take place
.The pollen grain lands on the surface of the stigma of the flower during pollination.
.The molecule on the surface of the pollen grain and the stigma interact
.If they recognize each other as being from the same species the pollen grain begins to grow or germinate.
.Germination will take place if they are the same species but from different plants
.A pollen tube begins to grow out from the tube cell of the pollen grain through the stigma into the style
.Tip of the pollen produces a hydrolytic enzyme to digest the tissue of the style, so pollen tube can make its way down between the cells
.Digestive tissue =nutient source of the pollen tube as it grows
.As the pollen tube grows down towards the ovary, the generative cell containing the generative nucleus travels down it
.The nucleus of this cell divide via mitosis as it moves down the tube to form two male nuclei
.Pollen tube grows through the ovary to reach an ovule and eventually the tip of the pollen tube passes through the micropyle of the ovule
.Two male nuclei are passed into the ovule so that fermentation can occur
81
What is Double fermentation
The process that occurs in plants in which one male nucleus fuses with the nuclei of the two polar nuclei to form the endosperm nucleus and the other fuses with the egg cell to form the diploid zygote
82
What is totipotent
| Give an example
A cell is able to develop into all different cell types
| A fertilised egg cell or zygote
83
What is the first step following fertilisation
| Explain this process
Cleavage
A process involving a special type of mitosis with no interphase that results in a mass of a small, undifferentiated cell
84
When does cleavage happen
As the embryo travels down the oviduct
85
What is a result of the cleavage
A mass of small, identical and undifferentiated cells forming a hollow sphere known as he blastocyte
86
What is a blastocyte
How long does this process take
A hollow ball of cells formed around five days of fertilisation
In humans, it takes 5-6 days
87
What is an embryonic stem cell
Cells in the early embryo that have the potential to form many other types of cells
88
What is meant by pluripotent
A cell is able to develop into most different cell types
89
What are pluripotent embryonic stem cells
Embryonic stem cells that can form many other types of cells
90
What is meant by cell determination
The predestination of cells to become particular types of tissues from early in the development of the embryo
91
What is meant by differentiate
Develop into significant types of cells
92
What is cell determination closely linked to
The position of the cells in the embryo
93
What happens as cell differentiation takes place
Different types of cells produce more and more protein specific to their cell type
