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aqa gcse biology free > T6 reproduction > Flashcards

T6 reproduction Flashcards

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1
Q

what is sexual reproduction

A

involves the production of gametes by meiosis

a gamete from each parent fuses to form a zygote

genetic information from each gamete is mixed so the resulting zygote is unique

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2
Q

what are gametes

A

sex cells (sperm and egg cells in animals, pollen and egg cells in flowering plants)

haploid (half the number of chromosomes)

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3
Q

what is meiosis

A

form of cell division involved in the formation of gametes in reproductive organs

chromosome number is halved

involves 2 divisions

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4
Q

what must occur prior to meiosis

A

interphase - copies of genetic information are made during this process

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5
Q

what happens during the first stage of meiosis

A

chromosome pairs line up along the cell equator

pair of chromosomes are separated and move to opposite poles of the cell

chromosome number is halved

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6
Q

what happens during the second stage of meiosis

A

chromosomes line up along the cell equator

chromatids are separated and move to opposite poles of the cell

four unique haploid gametes are produced

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7
Q

why is meiosis important for sexual reproduction

A

increases genetic variation

ensures that the zygote formed at fertilisation is diploid

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8
Q

describe fertilisation and its resulting outcome

A

gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis

as the embryo develops, cells differentiate

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9
Q

advantage of sexual reproduction

A

creates genetic variation in offspring, increasing chances of species adapting and surviving environmental changes

natural selection can be speeded up by humans in selective breeding to increase food production

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10
Q

disadvantages of sexual reproduction

A

two parents required making reproduction difficult in endangered populations or in species which have solitary lifestyles

more time and energy is required so fewer offspring are produced

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11
Q

what is asexual reproduction

A

involves mitosis only

produces genetically identical offspring known as daughter cells

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12
Q

advantages of asexual reproduction

A

1 parent required

lots of offspring produced quickly, enabling rapid colonisation of an area and reducing competition from other species

requires less energy and time as don’t need mate

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13
Q

disadvantage of asexual reproduction

A

no genetic variation reducing the chances of a species being able to adapt to environmental change

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14
Q

describe the circumstances in which malarial parasites reproduce sexually and asexually

A

sexual in mosquito

asexual in human host

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15
Q

describe the circumstances in which fungi and plants reproduce sexually and asexually

A

a - spores, seeds

s - to give variation, runner or bulb division

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16
Q

what is DNA

A

double-stranded polymer of nucleotides would to form a double helix

genetic material of the cell found in its nucleus

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17
Q

define genome

A

entire genetic material of an organism

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18
Q

why is understanding the human genome important

A

important for development of medicine

searching for genes linked to disease

understanding and treating inherited disorders

tracing human migration patterns from the past

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19
Q

what is a chromosome

A

long, coiled molecule of DNA that carries genetic information in the form of genes

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20
Q

define gene

A

small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein

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21
Q

what are the monomers of DNA

A

nucleotides

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22
Q

what are DNA nucleotides made of

A

common sugar
phosphate group
A T C G

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23
Q

full names of the four bases in nucleotides

A

adenine
thymine
cytosine
guanine

24
Q

describe how nucleotides interact to form a molecule of DNA

A

sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand

base connected to each sugar

complementary base pairs joined by weak hydrogen bonds

25
Q

explain how a gene codes for a protein

A

sequence of three bases in a gene forms a triplet

each triplet codes for an amino acid

order of amino acids determines the structure and function of protein formed

26
Q

why is the folding of amino acids important in proteins such as enzymes

A

determines the shape of the active site which must be highly specific to the shape of its substrate

27
Q

what is protein synthesis

A

formation of a protein from a gene

28
Q

two stages of protein synthesis

A

transcription

translation

29
Q

what does transcription involve

A

formation of mRNA from a DNA template

30
Q

outline transcription

A

DNA double helix unwinds

RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand

RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand

mRNA formation complete, mRNA detaches and leaves the nucleus

31
Q

what does translation involve

A

ribosome joins amino acids in a specific order dictated by mRNA to form a protein

32
Q

outline translation

A

mRNA attaches to a ribosome

ribosome reads the mRNA bases in triplets

Each triplet codes for 1 amino acid which is brought to the ribosome by a tRNA molecule (carrier molecule)

polypeptide chain is formed from the sequence of amino acids which join together

33
Q

what is a mutation

A

random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variants of the protein

occur continuously

34
Q

describe the effect of a gene mutation in coding DNA

A

if a mutation changes the amino acid sequence, protein structure and function may change (enzyme may no longer fits its substrate binding site or a structural protein may lost its strength)

if a mutation doesn’t change amino acid sequence, there is no effect on protein structure or function

35
Q

what is non-coding DNA

A

DNA which doesn’t code for a protein but instead controls gene expression

36
Q

describe the effect of a gene mutation in non-coding DNA

A

gene expression may be altered, affecting protein production and the resulting phenotype

37
Q

what are alleles

A

different versions of the same gene

38
Q

what is a dominant allele

A

version of a gene where only 1 copy is needed for it to be expressed

39
Q

what is a recessive allele

A

version of a gene where 2 copies are needed for it to be expressed

40
Q

what is meant when an organism is homozygous

A

when an organism has 2 copies of the same allele

41
Q

what is meant when an organism is heterozygous

A

when an organism has 2 different versions of the same gene

42
Q

what is the genotype

A

gene present for a trait

43
Q

what is the phenotype

A

visible characteristic

44
Q

problem with single gene crosses

A

most characteristics are controlled by multiple alleles rather than just one

45
Q

what is an inherited disorder

A

disorder caused by the inheritance of certain alleles

46
Q

how are embryos screened for inherited disorders

A

During IVF, one cell is removed and tested for disorder-causing alleles

if the cell doesn’t have any indicator alleles, then the originating embryo is implanted into the uterus

47
Q

what are the ethical issues concerning embryo screening

A

could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority

destruction of embryos with inherited disorders is seen by some as murder as these would go on to become humans

could be viewed as part of concept of designer babies as it may be for the parents convenience or wishes rather than child’s wellbeing

48
Q

what are the economic issues concerning embryo screening

A

costs of hospital treatment and medication will need to be considered if it is known that a child will have an inherited disorder and financial support explored if necessary

49
Q

social issues concerning embryo screening

A

social care for children with IH may need to be considered if parents are unable to provide care

if an embryo is found to have an IH and is terminated, this can prevent a child and its parents from potential suffering in the future due to the disorder

50
Q

what is gene therapy

A

insertion of a normal allele into the cells of a person with an IH to functionally replace the faulty allele

51
Q

ethical concerns surrounding gene therapy

A

going against and playing God

introduced genes could enter sex cells and so be passed to future generations

52
Q

sex chromosomes

A

M: XY
F: XX

53
Q

why does the inheritance of a Y chromosome mean that an embryo develops into a male

A

testes development in an embryo is stimulated by a gene present on the Y chromosome

54
Q

what is a sex-linked characteristic

A

characteristic that is coded for by an allele found on a sex chromosome

55
Q

why are men more likely to show the phenotype for a recessive sex-linked trait than women

A

many genes are found on X chromosome that have no counterpart on the Y chromosome

women (XX) have 2 alleles for each sex-linked gene whereas men (XY) often only have 1 allele

only 1 recessive allele is required to produce the recessive phenotype in males

56
Q

why are the majority of genes found on the X chromosome rather than the Y chromosome

A

X chromosome is bigger than Y so more genes are carried on it

aqa gcse biology free (25 decks)

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