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Topic 3 : Voice of the genome > 3.6 - 3.9 : Reproduction > Flashcards

3.6 - 3.9 : Reproduction Flashcards

1
Q

What are gametes ?

A
  • Gametes are sex cells (the sperm and egg in humans).
  • Gametes are haploid which means they contain half the number of chromosomes as the rest of the cells which make up our body.
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2
Q

What is fertilisation ?

A

the nucleus of the sperm cell fuses with the nucleus of the egg cell - this fusion of nuclei is called fertilisation

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3
Q

What is a zygote ?

A

When two gametes fuse during sexual reproduction, the fertilised egg (called a zygote) contains the full number of chromosomes i.e. it is diploid.

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4
Q

Describe and ?>explain the process of fertilisation to include the acrosomal and cortical reactions.

A
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5
Q

The Acrosome Reaction

A

When a sperm reaches the egg cell,
it binds to its outer layer (the zona pellucida) through attachment to sperm-binding proteins.
Once bound, it releases the digestive enzymes that are contained in the acrosome.
These enzymes digest a tunnel through the zona pellucida so that the sperm can reach the plasma membrane of the egg cell.
The plasma membranes of the sperm cell and the egg cell fuse
and the sperm releases its nucleus into the egg cell cytoplasm.
The nuclei of the sperm and egg fuse fertilisation has taken place and a zygote is formed.

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6
Q

The Cortical Reaction

A

The fusion of the sperm cell and egg cell membranes triggers the release of calcium ions which stimulates vesicles containing cortical granules to move and fuse with the egg cell membrane.
The cortical granules are released into the zona pellucida, which continue breaking down the zona pellucida, removing the remaining sperm-binding proteins so that no further sperm can bind.
Other substances within the cortical granules produce a new outer layer which is thick and impenetrable to sperm cells.
This process prevents multiple sperm cells from fertilising the egg, which would result in the zygote having an abnormal number of chromosomes.

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7
Q

Egg cells

A

Egg cells are specialised for fertilisation in the following ways:

  • Cytoplasm contains nutrients for growth of the developing embryo.
  • There is an outer layer called the zona pellucida this changes after fertilisation so that no further sperm can penetrate.
  • Follicle cells outside the zona pellucida form a protective coating around the egg cell.
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8
Q

Sperm cells

A

Sperm cells are also specialised to carry out fertilisation:

Overall streamlined shape for faster swimming.

Tail (flagellum) enables the sperm to swim.

Contain lots of mitochondria to provide ATP for movement.

The head of the sperm contains the acrosome- this is filled with digestive enzymes which break down the egg’s zona pellucida and allow the sperm to reach the egg cell membrane.

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9
Q
A
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10
Q

Blurt everything you know about crossing over as well as drawing a diagram.

A
  • Crossing over refers to the exchange of genetic material between homologous chromosomes.
  • A Chromatids with a different combintion of alleles are produced.
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11
Q

Blurt everything you know about independent assortment.

A
  • During metaphase I. Homologous chromosomes line up at the metaphase plate independently of each other.
  • As a result, the orientation of each pair of homologous chromosomes is random, leading to different combinations of chromosomes being produced.
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12
Q

Explain how crossing over and independent assortment can produce gametes with new
combinations of the alleles shown on the diagram of the two pairs of chromosomes.
(4)

A
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13
Q

Blurt everything you know about meiosis.

A
  • Meiosis is the cell division that produces gametes for sexual reproduction.
  • It produces four genetically different daughter cells.
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14
Q

Stages of meiosis ( not required to know but good to learn )

A
  • Meiosis I :

Prophase I: chromatids condense and arrange themselves into **homologous pairs **(called bivalents). Crossing over occurs . The nuclear envelope disintegrates and spindle fibres form.

Metaphase I: homologous chromosomes line up along the equator and attach to the spindle fibre by their centromeres. (don’t confuse centromeres with centrioles. A way to remeber is that centromerse have the letter C & M meaning they are the circle structure in the middle of chromosomes.)

Anaphase I: homologous chromosomes are separated.

Telophase I: chromosomes reach opposite poles of the cell. Nuclear envelope reforms around the chromosomes. Cytokinesis results in the formation of two daughter cells.

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15
Q

What is the locus ?

A

It is the location of a genes on a chromosomes.

The plural of locus is loci.

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16
Q

What is meant by autosomally linked ?

A

Alleles that are on the same chromosome.

  • so crossing over is less likey to occcur between these two genes.
  • Think of it like automtically linked, meaning they are on the same chromosome, so they are most likely to be inheritred together as crossing over is less likely to ocure between them.
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17
Q

Blurt everything you know about linked genes.

A

If the loci of two different genes are on the same chromosome, they are likely to be inherited together and are said to be linked.

The only way that the genes will not be inherited together is if crossing over separates them during meiosis (the chiasmata would have to form between the two genes.
The closer the loci of the two genes, the less likely this is to happen and the higher the probability that the genes will be inherited together.

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18
Q

Blurt everything you know about sex linkage.

A
  • Genes that are located on one of the sex chromosomes ( X or Y ) are said to be sex linked.
  • If the recessive allele (which causes disease) for a gene is found on the X-Chromosome, men will be more likely to inherit the disease as they only need 1 not 2 of that allele for the disease to be present in contrast to women where they need two as they have two X-chromosomes if they have one allele they will just be considered as a carrier of that disease.

e.g hemophilia and red-green colorblindness.

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19
Q
A
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20
Q

At the start of fertilisation, many sperm cells will surround the ovum.
Describe the events of fertilisation that occur after the acrosome reaction.
(3)

A
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21
Q
A
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22
Q

During fertilisation, only one sperm cell can fertilise an egg cell.
Explain why a second sperm cell cannot fertilise the egg cell.
(3)

A
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23
Q

Duchenne muscular dystrophy (DMD) is a sex-linked disorder.
(i) Explain what is meant by the term sex-linked disorder.
(2)

A
24
Q

Teratozoospermia is a condition that causes sperm cells to have an abnormal
structure. This condition reduces fertility.

A
25
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26
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27
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28
Q

Explain how crossing over may differ in sex chromosomes. (2)

A
29
Q
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30
Q

Explain why DNA is replicated before mitosis begins. (2)

A
31
Q

Explain how large numbers of cells with the same phenotype can be produced in a
tissue. (2)

A
32
Q

Name the part of a chromosome that is occupied by a gene. (1)

A

Locus.

33
Q

Explain which chromosome shows the weakest linkage between genes 1 and 2. (3)

A
34
Q
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34
Q

Sperm cells have adaptations for their function as male gametes.
Describe how the acrosome is involved in the digestion of the zona pellucida. (2)

A
35
Q

*(iii) During IVF treatment, egg cells are extracted from the ovaries.
Large numbers of sperm cells can be added to these egg cells in a Petri dish to
increase the chances of successful fertilisation.
In a study of 200 extracted egg cells, there was damage to the zona pellucida
of 13 of these egg cells.
Comment on the frequency of polyspermy due to IVF procedures.
(6)

A
36
Q

Give a reason for the high density of mitochondria found in the midpiece of a sperm cell.
(1)

A
37
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A
38
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38
Q

A sperm cell contains a specialised lysosome called the acrosome.
Describe the role of the acrosome in fertilisation. (3).

A
39
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40
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41
Q

chromosome vs homologus pair of chromosomes

A
  • Chromosome : A chromosome is a package of DNA with part or all of the genetic material of an organism.
  • A pair of chromosome with approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci.
42
Q

What is mitosis ?

A

Mitosis is a type of cell division where cells produce 2 genetically identical daughter cells.

  • It is used for growth and repair as well as asexual reproduction.
43
Q

Name the stages of th cell cycle ( Cell cycle ≠ Mitosis)

A
  1. **Interphase :
    • This consists of 3
      Growth phases       ( G1
      phase, S phase and
      G2 phase). This is where
      DNA replication takes
      place.
  2. Mitosis :
    • This is where the cells
      divide       and produce 2
      daughter cells each.
44
Q

Explain prophase

A

Prophase - the chromosomes condense into individual chromosomes (they become more visible) and the nuclear envelope(membrane) breakdown. The centrioles move to opposite poles of the cell and form spindle fibres.

45
Q

Explain metaphase

A

Metaphase - the chromosomes line up along the middle of the cell. They attach to the spindle fibre by their centromere.

46
Q

Explain anaphase

A

Anaphase - the centromere splits and the chromatids are pulled to opposite poles of the cell

47
Q

Explain telophase

A

Telophase - The two groups of chromsomes decondense (they become long and thin) and a nuclear envelope reforms around them, This results in two separate nuclei within a single cell.

48
Q

Explain cytokinesis

A

Cytokinesis - The cytoplasm divides and the plasma membrane pinches off to form two new, genetically-identical cells.Each with its own nucleus and cytoplasm.

49
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50
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51
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52
Q

(iii) Describe how a slide can be prepared from a root tip sample to produce this image.(3)

(iv) The mitotic index gives the percentage of cells in a sample undergoing mitosis.
Calculate the mitotic index for the 30 cells in this image. (2)

A
53
Q

What is asexual reproduction ?

A

The production of genetically identical offspring from one parent through the process of mitosis.

54
Q

Describe how meiosis leads to genetic variation in the gametes produced

A
55
Q

Explain why some genes show linkage and other genes shoe sex-linkage

A

There are many genes on each chromosome

Topic 3 : Voice of the genome (4 decks)

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