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Biology - Inheritance, variation and evolution > Reproduction > Flashcards

Reproduction Flashcards

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1
Q

What is sexual reproduction?

A
  • Type of reproduction.
  • 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 such as 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) 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

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

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6
Q

What happens during the second stage 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 asexual reproduction?

A
  • Type of reproduction.
  • Involves mitosis.
  • Produces genetically identical offspring known as daughter cells.
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10
Q

What is DNA?

A

A double stranded polymer of nucleotides, which form a double helix.
The genetic material of the cell found in its nucleus.

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11
Q

Define genome

A

The entire genetic material of an organism.

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12
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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13
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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14
Q

How many chromosomes do human body cells have?

A

46 chromosomes (23 pairs).

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15
Q

How many chromosomes do human gametes have?

A

23 chromosomes.

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16
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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17
Q

What are monomers of DNA?

A

Nucleotides.

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18
Q

What are DNA nucleotides made up of?

A
  • Common sugar.
  • Phosphate group.
  • One of the four bases: A, T, C or G.
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19
Q

State the full names of the four bases found in nucleotides

A
  • Adenine.
  • Thymine.
  • Cytosine.
  • Guanine.
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20
Q

Describe how nucleotides interact to form a molecule of DNA

A
  • Sugar and phosphate molecules to form a sugar-phosphate backbone in each DNA stand.
  • Base connected to each sugar.
  • Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds.
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21
Q

Explain how a gene codes for a protein

A
  • A sequence of three bases in a gene forms a triplet code.
  • Each triplet codes for an amino acid.
  • The order of amino acids determines the structure (such as how it will fold) and function of the protein formed.
22
Q

Why is the ‘folding” of amino acids important in proteins such as enzymes?

A

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

23
Q

What is protein synthesis?

A

The formation of a protein from a gene.

24
Q

What are the 2 stages of protein synthesis?

A

1) Transcription.

2) Translation.

25
Q

What does transcription involve?

A

The formation of mRNA from a DNA template.

26
Q

Outline transcription

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 strands.
4) mRNA formation complete. mRNA detaches and leaves the nucleus.

27
Q

What does translation involve?

A

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

28
Q

Outline translation

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 by a tRNA molecule (carrier molecule).
3) A polypeptide chain is formed from the sequence of amino acids which join together.

29
Q

What is a mutation?

A

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 (slight alteration but appearance and function remains).
Mutations occur continuously.

30
Q

Describe the effect of a gene mutation in DNA

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 the amino acid sequence, there is no effect on protein structure or function.
31
Q

What is non-coding DNA?

A

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

32
Q

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

A

Gene expression may be altered, affecting protein production (switch genes on or off) and the resulting phenotype.

33
Q

What are alleles?

A

Different versions of the same gene.

34
Q

What is a dominant allele?

A

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

35
Q

What is a recessive allele?

A

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

36
Q

What is meant when an organism is homozygous?

A

When an organism has 2 copies of the same allele (2 recessive or 2 dominant).

37
Q

What is meant when an organism is heterozygous?

A

When an organism has 2 different versions of the same gene (one dominant and one recessive).

38
Q

What is the genotype?

A

The genes present for a trait.

39
Q

What is the phenotype?

A

The visible characteristic.

40
Q

How are dominant alleles represented in a punnett square?

A

They are represented using uppercase letters.

41
Q

How are recessive alleles represented in a punnett square?

A

The use lowercase version of the same letter as the dominant allele.

42
Q

What is the problem with single gene crosses?

A

Most characteristics are controlled by multiple alleles rather than just one.

43
Q

What is an inherited disorder?

A

A disorder causes by the inheritance of certain alleles.

44
Q

Give 2 examples of inherited disorders

A
  • Polydactyly (having extra fingers or toes) - caused by a dominant allele.
  • Cystic fibrosis (a disorder of cell membranes) - caused by a recessive allele.
45
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.

46
Q

What are 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 parents convenience or wishes rather than the child’s wellbeing.
47
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.
48
Q

What are the social issues concerning embryo screening?

A
  • Social care for children with inherited disorders may need to be considered if parents cannot provide care.
  • If an embryo is found to have an inherited disorder and is terminated, they can prevent a child and its parents from potential suffering in the future due to the disorder.
49
Q

What is gene therapy?

A

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

50
Q

What are the ethical issues concerning gene therapy?

A
  • Some people believe it is going against and ‘playing God’.

- Introduced genes could enter sex cells and be passed to future generations.

Biology - Inheritance, variation and evolution (4 decks)

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