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GCSE AQA Biology 9-1 > B13 Reproduction > Flashcards

B13 Reproduction Flashcards

1
Q

what are gametes?

A

a cell where the chromosomes are not paired

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2
Q

how are gametes made?

A

by a type of cell division called meiosis

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3
Q

what does sexual reproduction involve?

A

the fusion of male and female gametes (fertilisation)
this means there is mixing of genetic information

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4
Q

what does asexual reproduction involve?

A

there is only one parent so it does not involve gametes
the offspring are genetically identical clones
it only involves mitosis

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5
Q

how many chromosomes are there in gametes?

A

23 single chromosomes

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6
Q

where does meiosis take place?

A

reproductive organs

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7
Q

what are the stages of meiosis?

A
  • all of the chromosomes are copied
  • the cell now divides into two
  • both of the cells now divide one more time forming the gametes
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8
Q

how many gametes does meiosis form?

A

4 gametes from the original cell

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9
Q

how may chromosomes does a cell have after fertilisation?

A

the normal number (23 pairs in humans)

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10
Q

what happens after the gametes have fused?

A

the cell divides by mitosis to form a ball of cells called an embryo

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11
Q

what are the advantages of sexual reproduction?

A

survival advantage by natural selection - offspring receive a mixture of genetic info. this produces variation which means some of the offspring may survive if the environment changes

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12
Q

what is the advantage of asexual reproduction?

A

only one parent is needed so it is more efficient in both time and energy. this means it is faster than sexual reproduction

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13
Q

what is the disadvantage to asexual reproduction?

A

it is very risky - all the offspring are genetically identical so could all die if the conditions are not favourable

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14
Q

how does the malaria parasite reproduce?

A

it reproduces asexually inside the human host
it uses sexual reproduction in the mosquito vector

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15
Q

how do fungi reproduce?

A

they reproduce asexually using spores
they can also reproduce sexually to produce variation in their offspring

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16
Q

how can flowering plants reproduce?

A

they can reproduce sexually to produce seeds
some can also reproduce asexually by sending out runners or by bulb division

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17
Q

why is DNA genetic material?

A

because DNA determines inherited features

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18
Q

what are DNA strands made from? (their structure)

A

they are a polymer
this means they are made by joining lots of smaller molecules together

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19
Q

what is the name of the structure of DNA?

A

the two strands wrap around each other in a double helix

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20
Q

what is a gene?

A

a small section of DNA on a chromosome

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21
Q

what does each gene encode for?

A

a specific sequence of amino acids to make a specific protein

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22
Q

what is the genome?

A

the entire genetic material for an organism

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23
Q

what are the advantages to investigating the whole of a genome?

A

it will help us to search for genes that are linked to diseases
it will help us to understand and treat inherited disorders
we can use the human genome to trace human migration patterns from the past

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24
Q

what molecules are DNA polymers made from?

A

nucleotides

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25
Q

what is the structure of a nucleotide?

A

a phosphate group is attached to a sugar molecule
the sugar molecule is then attached to a base

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26
Q

what changes and what does not change in DNA?

A

the phosphate group and the sugar molecule never change
there are four different bases (A, C, G and T)

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27
Q

what does it mean by the DNA strands are complementary?

A

the same bases pair on the opposite strands

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28
Q

which bases pair to each other?

A

A always links to T
G always links to C

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29
Q

what is a protein?

A

a polymer (chain) of amino acids

30
Q

how many different amino acids are there?

A

20 in humans

31
Q

what does the order of amino acids affect in a protein?

A

the shape of the protein which determines its function

32
Q

what is the sequence of amino acids in a protein controlled by?

A

the sequence of bases in a gene

33
Q

what encodes for an amino acid?

A

a triplet of bases encodes for a specific amino acid

34
Q

where does transcription take place?

A

the nucleus

35
Q

where does translation take place?

A

the cytoplasm

36
Q

what is transcription?

A
  • the base sequence of the gene is copied into a complementary template molecule (mRNA)
  • the mRNA then passes out of the nucleus through tiny pores into the cytoplasm
37
Q

what are the key features of mRNA?

A

it is complementary to the base DNA strand
it is only one strand
it is small enough to leave the nucleus

38
Q

what happens during translation?

A
  • the mRNA molecule attaches to a ribosome
  • amino acids are then brought to the ribosome on tRNA (carrier molecules)
  • the ribosome then reads the triplets of bases on the mRNA and joins the amino acids in the correct order
39
Q

what happens once a chain of amino acids is complete?

A

it folds into its unique shape

40
Q

what are the bonds which hold the two strands of DNA together?

A

peptide bonds

41
Q

what is a mutation?

A

a change of a base in the DNA strand

42
Q

what do many mutations not do?

A

change the amino acid in the chain
this is because different base triplets can often encode for the same amino acid

43
Q

what can some mutations do?

A

alter an amino acid in the chain.
this causes the shape and function of the protein to be changed

44
Q

what can happen if the mutation changes the shape of an enzyme?

A

it can change the shape of the active site so the enzyme no longer binds to the substrate
or
it can cause the enzyme to improve its function or catalyse a different reaction

45
Q

what can happen if a mutation changes the shape of a structural protein?

A

it can cause the protein to lose its strength
or
have improved strength

46
Q

what do non-coding parts of DNA do?

A

they switch genes on and off

47
Q

what happens when mutations in non-coding parts of DNA occur?

A

it can affect which parts of genes are switched on and off
this can have a significant effect on the function of a protein or the cell

48
Q

where do the chromosomes come from?

A

one from mother
one from father

49
Q

what are alleles?

A

versions of the same gene

50
Q

what is a genotype?

A

the alleles present on a person’s chromosomes

51
Q

what does homozygous mean?

A

a person has two copies of the same allele

52
Q

what is a phenotype?

A

a characteristic caused by a person’s alleles

53
Q

what does heterozygous mean?

A

when a person has two different alleles for a gene

54
Q

what phenotype does a heterozygous person have?

A

the dominant allele will be expressed in the phenotype even if there is only one dominant allele present

55
Q

what is a recessive allele?

A

an allele which will only show in the phenotype if there are two copies present

56
Q

what is cystic fibrosis?

A

a disorder of cell membranes which is controlled by a single gene which has two alleles.

57
Q

which allele of cystic fibrosis causes defective cell membranes?

A

the recessive one

58
Q

what is a carrier of cystic fibrosis?

A

a person with a heterozygous genotype (Cc)

59
Q

what is the genotype for a person with cystic fibrosis?

A

homozygous with the recessive c allele (cc)

60
Q

what is polydactyly?

A

when someone has extra phalanges (fingers or toes)

61
Q

what is polydactyly caused by (in terms of alleles)?

A

a dominant allele

62
Q

why can you not be a carrier of polydactyly?

A

polydactyly is caused by a dominant allele so even if there is only one present in the genotype, it will be expressed in the phenotype

63
Q

what is embryo screening?

A

when embryos are tested to see if they have the alleles for genetic disorders

64
Q

what are some issues with embryo screening?

A
  • expensive, money should be spent elsewhere
  • unethical (when pre-implantation screening is done), large numbers of embryos are created but not all are used. this means healthy embryos are destroyed
  • increases the risk of a miscarriage
  • designer babies
65
Q

what is gene therapy?

A

when scientists correct faulty alleles
STILL EXPERIMENTAL

66
Q

what does a family tree show?

A

phenotypes, not genotypes

67
Q

how do you know cystic fibrosis is caused by a recessive allele from a family tree?

A

if neither parent has cystic fibrosis but a child does, it shows that it must be a recessive allele and the parents are carriers. if cystic fibrosis was dominant, then at least one parent would have to have the disease to pass it on to the child.

68
Q

what are the sex chromosomes for a male?

A

XY (different)

69
Q

what are the sex chromosomes for a female?

A

XX (the same)

70
Q

what chromosomes do female gametes have?

A

all have X chromosomes

71
Q

what chromosomes do male gametes have?

A

half have X
half have Y

72
Q

what is the ratio/percentage of male and female offspring?

A

50% are female
50% are male
1:1

GCSE AQA Biology 9-1 (20 decks)

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