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AQA GCSE Biology > 6.1 Reproduction (Triple) > Flashcards

6.1 Reproduction (Triple) Flashcards

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1
Q

What is sexual reproduction?

A

A type of reproduction involving 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 (non-identical haploid cells) in reproductive organs

● Chromosome number is halved

● Involves two 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
  1. Chromosome pairs line up along the cell equator
  2. The pair of chromosomes are separated and move to opposite poles of the cell (the side to which each chromosome is pulled in random, creating variation).
  3. Chromosome number is halved
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6
Q

What happens during the second phase of meiosis?

A
  1. Chromosomes line up along the cell equator
  2. The chromatids are separated and move to opposite poles of the cell
  3. Four unique haploid gametes are produced
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7
Q

Why is meiosis important for sexual reproduction? (2)

A

● It increases genetic variation

● It 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 (which increases the number of cells).
As the embryo develops, cells differentiate.

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9
Q

What is the advantage of sexual reproduction? (Triple)

A

It creates genetic variation in offspring, increasing the probability of a species adapting to 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

Describe the disadvantages of sexual reproduction. (2) (Triple)

A

Two parents are required. This makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles.

More time and energy is required so fewer offspring are produced

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11
Q

What is asexual reproduction? (Triple)

A

● Type of reproduction

● Involves mitosis only

● Produces genetically identical offspring known as daughter cells

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12
Q

Describe the advantages of asexual reproduction. (3) (Triple)

A

● Only one parent is required

● Lots of offspring can be produced in a short period of time enabling the rapid colonisation of an area and reducing competition from other species

● Requires less energy and time as a mate is not needed

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13
Q

What is the disadvantage of asexual reproduction? (Triple)

A

No genetic variations (except from spontaneous mutations) which reduces the probability 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 reproduction occurs in the mosquito whilst asexual reproduction occurs in the human host

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15
Q

Describe the circumstances in which fungi reproduce sexually and asexually

A

Asexual reproduction is by the spores. Sexual reproduction to give variation.

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16
Q

Describe the circumstances in which plants reproduce sexually any sexually

A

Sexual reproduction to produce seeds. Asexual reproduction by runners (e.g. strawberry plants or bulb division e.g. daffodils)

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17
Q

What is DNA?

A

A double-stranded polymer of nucleotides round to form a double helix. It is the genetic material of a cell which is found in its nucleus.

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18
Q

Define genome

A

The entire genetic material of an organism

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19
Q

Why is understanding the human genome important?

A

The whole human genome has been studied and is important for the development of medicine in the future

● Searching for genes linked to different types of disease

● Understanding and treating inherited disorders

● Tracing human migration patterns from the past

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20
Q

What is a chromosome?

A

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

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21
Q

How many chromosomes do human body cells have?

A

46 chromosomes (23 pairs)

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22
Q

How many chromosomes do human gametes have?

A

23 chromosomes

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23
Q

Define gene

A

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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24
Q

What are the monomers of DNA? (Triple)

A

Nucleotides

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25
Q

What are DNA nucleotides made up of? (Triple)

A

● Simple sugar

● Phosphate group

● One of the 4 bases: A, T, C or G

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26
Q

State the full names of the four bases found in nucleotides. (Triple)

A

● Adenine
● Thymine
● Cytosine
● Guanine

27
Q

Describe how nucleotides interact to form a molecule of DNA. (Triple, Higher)

A

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

● Base connected to a sugar

● Complementary base pairs (A pairs
with T, C pairs with
G) joined by weak hydrogen bonds

28
Q

Explain how a gene codes for a protein. (Triple)

A

● A sequence of three bases in a gene forms a triplet

● Each triplet codes for an amino acid

● The order of amino acids determines the structure (i.e. how it will fold) and function of the protein formed

29
Q

Why is the ‘folding’ of amino acids important in proteins such as enzymes? (Triple, Higher)

A

The folding of amino acids determines the shape of the active site which must be highly specific to the shape of the substrate.

30
Q

What is protein synthesis? (Triple, Higher)

A

The formation of a protein from a gene

31
Q

What are the two stages of protein synthesis? (Triple, Higher)

A
  1. Transcription
  2. Translation
32
Q

What does transcription involve? (Triple, Higher)

A

The formation of mRNA from a DNA template

33
Q

Outline transcription. (Triple, Higher)

A
  1. DNA double helix unwinds
  2. RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
  3. RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
  4. mRNA formation complete. mRNA detaches and leaves the nucleus
34
Q

What does translation involve? (Triple, Higher)

A

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

35
Q

Outline translation. (Triple, Higher)

A
  1. mRNA attaches to a ribosome
  2. Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome with a tRNA molecule (carrier molecule)
  3. A polypetide chain is formed in the sequence of amino acids when joined together
36
Q

What is a mutation? (Triple, Higher)

A

A random change in the base sequence of DNA which results mostly in no change for the protein coded for, or genetic variants of the protein (slight alteration but appearance and function remain).
Mutations occur continuously.

37
Q

Describe the effect of a gene mutation in coding DNA. (Triple, Higher)

A

● If a mutation changes the amino acid sequence, protein structure and function may change (an enzyme may no longer fit its substrate binding site or a structural protein may lose its strength).

● If a mutation does not change amino acid sequence, there is no effect on protein structure and function.

38
Q

What is non-coding DNA? (Triple, Higher)

A

DNA which does not code for a protein but instead controls gene expression.

39
Q

Describe the effect of a gene mutation in non-coding DNA. (Triple, Higher)

A

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

40
Q

What are alleles?

A

Alleles are different versions of the same gene

41
Q

What is a dominant allele?

A

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

42
Q

What is a recessive allele?

A

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

42
Q

What is meant when an organism is homozygous?

A

When an organism has two copies of the same allele (two recessive or two dominant).

43
Q

What is meant when an organism is heterozygous?

A

When an organism has two different versions of the same gene (one dominant and one recessive).

44
Q

What is the phenotype?

A

The visible characteristic

45
Q

What is a genotype?

A

The genes present for a trait

46
Q

How are dominant alleles represented in a punnett square?

A

They are represented using uppercase letters

47
Q

How are recessive alleles represented in a punnett square?

A

They use the lowercase version of the same letter as the dominant allele

48
Q

PKU is a recessive condition. Two heterozygous parents (Pp) have offspring. Predict the proportion of offspring that will have PKU.

A

75% chance of normal phenotype

25% chance of PKU phenotype

49
Q

What is the problem with single gene crosses?

A

Most characteristics are controlled by multiple alleles rather than just one

50
Q

What is an inherited disorder?

A

A disorder caused by the inheritance of certain alleles

51
Q

Give two examples of inherited disorders

A

● Polydactyly (having extra fingers and toes), caused by a dominant allele

● Cystic Fibrosis (a disorder of cell membrane), caused by a recessive allele

52
Q

How are embryos screened for inherited disorders?

A

During IVF, one cell is removed (from an 8 cell embryo) and tested for disorder-causing alleles. If the cell doesn’t have any indicator alleles, then the originating embryo is implanted into the uterus.

52
Q

What are the ethical issues concerning embryo screening?

A

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

● The destruction of embryos with inherited disorders is seen by some as murder as these would go on to become human beings.

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

53
Q

What are the economic issues concerning embryonic 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.

54
Q

What are the social issues concerning embryonic screening?

A

● Social care for children with inherited disorders may need to be considered if parents are unable to provide care.

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

55
Q

What is gene therapy?

A

The insertion of a normal allele into the cells of a person with an inherited disorder to functionally replace the faulty allele.

56
Q

What are the ethical issues concerning gene therapy?

A

● Some people believe it goes against God as people are ‘playing God’

● The introduced genes could enter sex cells and be transferred to future generations

57
Q

What are sex chromosomes?

A

A pair of chromosomes that determine sex:

● Males have an X and Y chromosome

● Females have two X chromosomes

58
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

59
Q

A couple have a child. What is the probability that the child is female?

A

50%

60
Q

What is a sex-linked characteristic?

A

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

61
Q

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

A

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

62
Q

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

A

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

● Women (XX) have two alleles for each sex-linked gene whereas men (XY) often only have one allele therefore only one recessive allele is required to produce the recessive phenotype in males.

AQA GCSE Biology (31 decks)

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