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Bio Paper 2 > B13: Reproduction > Flashcards

B13: Reproduction Flashcards

1
Q

How many pairs of chromosomes do human cells have?

A

23 :>

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2
Q

In what type of cell are chromosomes not paired?

A

Gametes (egg and sperm cells in humans).

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3
Q

How do gametes divide?

A

Meiosis

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4
Q

What are the features of meiosis?

A

Meiosis produces non identical cells.
Takes place in flowering plants (gametes are pollen and egg cells)

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5
Q

What are the features of sexual reproduction?

A

Involves the fusion of male and female gametes (fertilisation). It means that in sexual reproduction, there is mixing of genetic information, meaning that offspring contains genetic material from both parents.

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6
Q

What are the features of asexual reproduction?

A

Involves only one parent and no gametes and no mixing of genetic information - so offspring are all genetically identical (Clones). No meiosis, only mitosis.
e.g. aphids, daffodils and strawberries.

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7
Q

How can a plant reproduce asexually using buds?

A

A plant can contain tiny buds on its leaf. They will then drop off and produce new plants, they are clones.

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8
Q

In what organs does meiosis take place?

A

Reproductive organs e.g. testes and ovaries.

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9
Q

What happens in meiosis?

A

1 - Chromosomes are copied, then cell divides into 2. The these 2 cells divide into 2 to form gametes, and chromosomes are now single and not paired. Meiosis has halved the number of chromosomes, producing 4 gametes from 1 original cell, and these gametes are genetically different from each other as they have different alleles?

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10
Q

Describe how gametes join during sexual reproduction

A

Male gamete joins with female gamete (fertilisation). The cell now has a normal number of chromosomes (23 pairs).

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11
Q

What happens after fertilisation?

A

New cell divides, producing a clump of identical cells, forming an embryo. As it develops its cells differentiate, forming different cell types e.g. nerve and muscle cells.

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12
Q

What are the advantages of sexual reproduction?

A

Variation in offspring - if environment changes, variation means that some of the offspring may survive, so the offspring has a survival advantage by natural selection.
Selective breeding - organisms with desirable characteristics produced

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13
Q

What are the advantages of asexual reproduction?

A

Only one parent needed - no need for mate, so more efficient (in terms of time and energy).
Faster.
Extremely useful in unfavourable conditions

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14
Q

What are the disadvantages of sexual reproduction?

A

Need a mate - lots of time and energy required.

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15
Q

What are the disadvantages of asexual reproduction?

A

No variation - organisms could die in unfavourable conditions

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16
Q

What is the life cycle of the malaria virus?

A

Part of cycle in mosquito vector, part in human.
In human, virus reproduces asexually, in mosquito, virus reproduces sexually.

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17
Q

How do fungi reproduce?

A

They produce spores - asexual.
Can also reproduce sexually.

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18
Q

How do flowering plants reproduce?

A

All flowering plants reproduce sexually to produce seeds e.g. a strawberry plant.

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19
Q

How do strawberry plants reproduce asexually?

A

Send out runners, when it touches soil, it will develop into a genetically identical plant.

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20
Q

How do daffodils reproduce asexually?

A

Through bulb division - parent has an underground bulb, which produces buds, which form new offspring plants (genetically identical).

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21
Q

What is DNA?

A

Genetic material because it determines our inherited features.

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22
Q

Describe the structure of DNA

A

Contains 2 long strands in a double helix shape (wrap around each other). Each strand is a polymer, made up of nucleotide monomers.

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23
Q

What is DNA in relation to chromosomes?

A

A gene is a small section of DNA on a chromosome.

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24
Q

What do genes do to amino acids?

A

Encodes a specific sequence of amino acids to make a specific protein.

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25
Q

What is the genome?

A

The entire genetic material of an organism e.g. human genome.

26
Q

What are the benefits of studying the human genome?

A

Helps us search for genes that are linked to a disease e.g. genes that increase the risk of cancer.
Helps us understand and treat inherited disorders e.g. cystic fibrosis.
Trace human migration patterns from the past - helps determine ancestry.

27
Q

What are the monomers that make up DNA called?

A

Nucleotides

28
Q

What are the 3 main parts of nucleotides?

A

Phosphate group - attached to…
Sugar molecule - attached to…
Base
(Phosphate and sugar never change, but there are 4 different bases)

29
Q

What are the 4 different bases?

A

A - Adenine
C - Cytosine
G - Guanine
T - Thymine

30
Q

What is the feature of DNA strands?

A

They are complimentary, means that the same bases always pair in the opposite strands.
e.g. A and T, C and G

31
Q

How many different amino acids are there in humans?

A

20

32
Q

What feature determines the shape of the protein?

A

The order of amino acids, which also determines its function.

33
Q

How is the order of amino acids in a protein determined?

A

By the sequence of bases in the gene for that protein.
The cell which makes the protein reads the DNA sequence as triplets of bases, and each triplet encodes for a specific amino acid in the protein.

34
Q

Where are the 2 stages of protein synthesis?

A

First stage in nucleus
Second stage in cytoplasm

35
Q

Describe the first stage of protein synthesis

A

Transcription - base sequence of the gene is copied into a complementary template molecule (Messenger RNA (mRNA), a single stranded molecule). It now passes out of the nucleus and into the cytoplasm.

36
Q

Describe the second stage of protein synthesis

A

Translation - the mRNA molecule attaches to a ribosome. Amino acids are now brought to the ribosome on carrier molecules (called transfer RNA (tRNA). Ribosome now reads the triplets of bases on the mRNA, and uses this to join together the correct amino acids in the correct order. Once the chain is complete, it folds into its unique shape, and enables the protein to do its job.

37
Q

What is a mutation?

A

A change to a base.

38
Q

How often do mutations happen?

A

All the time

39
Q

Why can mutations not have an effect sometimes?

A

For proteins, multiple triplets of base pairs can encode for the same amino acid, therefore no change is made to the protein, so there is no effect on the shape and function of the protein. Most mutations have no effect on the function of the protein.
(however, if a mutation changes the amino acid completely, it can have a dramatic effect on the function of the protein (e.g. collagen loses strength))

40
Q

What is the function of the non-coding part of chromosomes?

A

The regions switch genes on and off e.g. tell genes when to produce proteins. Mutations in these regions can affect how genes are switched on and off (e.g. may be turned on when its meant to be off, which could result in a significant effect such as uncontrolled mitosis, leading to cancer)

41
Q

Where do the chromosomes in our cells come from?

A

They come in pairs - in each pair, one chromosome comes from the mother and the other from the father.

42
Q

How many copies of every gene do we have?

A

Gene - a section of DNA on a chromosome.
Two copies of every gene.

43
Q

What is an allele?

A

Different versions of the same gene.

44
Q

What is the genotype of a person?

A

Tells us what alleles are present

45
Q

What is the phenotype of a person?

A

The physical characteristics of a person e.g. dry ear wax…

46
Q

What does homozygous mean?

A

A person who has the two copies of the same allele

47
Q

What does heterozygous mean?

A

A person with two different alleles e.g. heterozygous ear wax genes :]

48
Q

If an allele is heterozygous, what characteristic will the person see (phenotype)?

A

The one encoded by the dominant allele.

49
Q

What is a recessive allele?

A

Will only show up in the phenotype if there are two copies present (if no dominant allele is present).

50
Q

What are some inherited disorders?

A

Cystic fibrosis
Polydactyly

51
Q

What is a dominant allele?

A

An allele that will always be expressed, even if there is only one copy present

52
Q

What is cystic fibrosis?

A

A disorder of cell membranes.
It is controlled by a single gene which has 2 alleles - the allele for normal cell function is dominant (C). The allele for defective cell membranes is recessive (c), therefore to have cystic fibrosis, the person must have 2 copies of the defective allele (inherit a defective allele from both parents).

53
Q

What is a carrier of the cystic fibrosis allele?

A

A person who has one defective allele, and one normal allele (they do not have cystic fibrosis themselves).

54
Q

What is polydactyly?

A

People who have extra fingers or toes

55
Q

What causes polydactyly?

A

A dominant allele - a person with one or two copies of the polydactyly allele with have the disorder.
You cannot be a carrier of the polydactyly allele. true of any dominant allele.

56
Q

What are some solutions for inherited disorders?

A

Embryo screening - embryos are tested to see if they have alleles for inherited disorders. Embryos which are not affected by disorders are implanted into the woman, and can then grow into healthy offspring.

57
Q

What are the issues with embryo screening?

A

Expensive - people think money is better spent elsewhere in the health service.
A large number of embryos are created, but only a small number are implanted, meaning some healthy embryos are destroyed which is unethical.
In future, we may be able to screen embryos to produce offspring with desirable features, which is unethical.

58
Q

What is gene therapy?

A

In the future, scientists may be able to correct faulty alleles and use this to treat inherited disorders. (still experimental)

59
Q

What does the family tree show?

A

Only phenotypes - no genotypes.

60
Q

What do the 22 of the chromosome pairs determine?

A

The inherited characteristics of an individual

61
Q

What does the 23rd chromosome determine?

A

It contains the genes that determine sex.
If the two chromosomes are different, it’s a male (X and Y chromosome).
If they’re the same, it’s a female (X and X).

Bio Paper 2 (10 decks)

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