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Edexcel iGCSE Biology > Inheritance > Flashcards

Inheritance Flashcards

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1
Q

What is a nucleus?

A

Contains all of the body’s genetic information in the form of 46 chromosomes

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2
Q

What is a chromosome?

A

Long lengths of DNA coiled up

Humans have 46 chromosomes or 23 pairs

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3
Q

What is a gene?

A

A short section of DNA.

It is a chemical instruction that codes for a particular protein

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4
Q

What is DNA?

Deoxyribo-Nucleic Acid

A

A long list of instructions on how to put an organism together and make it work

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5
Q

Describe the structure of a DNA molecule.

A
  1. Two strands coil together in a double helical shape
  2. Strands are held together by bases (special chemicals)
  3. The bases are paired and they will always pair up in the same way: A-T and C-G (complementary base pairing)
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6
Q

What are the four bases in a DNA molecule and which pair with which?

A

Adenosine
Thymine
Guanine
Cytosine

Adenosine + Thymine
Cytosine + Guanine

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7
Q

What is DNA’s role in a cell?

A

Controls the production of proteins (protein synthesis)

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8
Q

How does a gene decide which protein is made?

A

The order of the bases in a gene decides the order of the amino acids

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9
Q

What is a codon?

A

A sequence of three bases in a gene. Codes for one amino acid

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10
Q

How many amino acid combinations are possible from one gene?

A

64

4 x 4 x 4

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11
Q

How many amino acids can be made?

A

20

Therefore some codons form the same amino acid

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12
Q

How many amino acids can be made?

A

20

Therefore some codons form the same amino acid

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13
Q

What are the two stages of protein synthesis?

A

Transcription
Translation

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14
Q

Where does protein synthesis occur?

A

In the nucleus (transcription) and in ribosomes (translation)

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15
Q

What is mRNA and why is it needed?

A

Messenger RNA

DNA can’t leave the nucleus because it’s too big, so mRNA transfers the gene data

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16
Q

What are the four bases in mRNA and which pair with which?

A

Adenosine
Uracil
Guanine
Cytosine

Adenosine - Uracil
Guanine - Cytosine

Thymine is replaced with Uracil

17
Q

What is RNA-polymerase?

A

The enzyme that joins together the base sequences to form mRNA

18
Q

How does transcription work?

A
  1. RNA-polymerase binds to a region of non-coding DNA
  2. The two DNA strands unzip and the RNA polymerase moves along one of the strands of DNA
  3. It uses the coding DNA in the gene as a template to make the mRNA
  4. Once made, the mRNA moves out of the nucleus and joins with a ribosome in the cytoplasm
19
Q

How does translation work?

A
  1. Amino acids are brought to the ribosome by tRNA (t = transfer)
  2. The order which the amino acids are brought to the ribosome matches the order of the codons in the mRNA
  3. The anti-codon on the tRNA is complementary to the codon on the amino acid.
  4. The pairing between codon and anti-codon makes sure that the amino acids are in the right order
  5. The amino acids are joined together by the ribosome, making a protein
20
Q

What is the definition of asexual reproduction?

A

Reproduction involving one parent. The offspring have identical genes to the parent so there’s no variation between parent and offspring

21
Q

What is mitosis?

A

When a cell reproduces by splitting itself in half to form two cells with identical sets of chromosomes

22
Q

What are the steps of mitsosis?

A
  1. Chromosomes in nucleus are copied (one copy for each new cell -> forms X-shaped chromosome)
  2. Chromosomes line up at centre of cell and cell fibres pull them apart
  3. Membranes form around each of the new set of chromosomes (become nuclei) and cytoplasm divides
  4. Two genetically identical daughter cells are made
23
Q

What is the definition of sexual reproduction?

A

The fusion of male and female gametes (haploid cells). Because there are two parents, the offspring contain a mixture of their parents’ genes

24
Q

What is meiosis?

A

Produces four haploid cells whose chromosomes are not identical.

Two divisions occur. The first is like mitosis, the second is different

25
Q

What are the steps of meiosis?

A
  1. Chromosomes in nucleus are copied (one copy for each new cell -> forms X-shaped chromosome)
  2. The chromosomes line up in pairs in the centre of the cell. Each pair will have a chromosome each from the mother and father
  3. The pairs are pulled apart so each cell will have both the father’s and mother’s chromosomes in each cell. This creates genetic variation
  4. In the second division, the chromosomes line up in the centre of the cell and the arms are pulled apart
  5. Four haploid gametes that are all genetically different. Each gamete only have a single set of chromosomes
26
Q

What are alleles?

A

Different variations of the same gene

27
Q

What is your genotype?

A

The alleles that you have

28
Q

What is your phenotype?

A

The physical characteristics the alleles produce

29
Q

What alleles can you have if you’re homozygous?

A

Two alleles of the same type for that gene e.g. AA or aa

30
Q

What alleles can you have if you’re heterozygous?

A

Two different alleles for that gene e.g. Aa

31
Q

What is a codominant allele?

A

When neither allele is recessive, so you show characteristics from both alleles.

E.g. blood group AB

32
Q

What is a mutation?

A

A rare, random change in an organism’s DNA that can be inherited

33
Q

What can increase the chance of a mutation?

A

Ionising radiation e.g. X-rays, gamma rays, UV rays

Chemicals called mutagens (e.g. tobacco smoke)

34
Q

How can bacteria evolve to become antibiotic resistant?

A
  1. Bacteria develop random mutations in their DNA which mean they’re less affected by that antibiotic
  2. This newly-resistant bacteria lives for longer and reproduces many times
  3. This leads to the allele for resistance being passed on to most of its offspring

Edexcel iGCSE Biology (10 decks)

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