Inheritance Flashcards
What is a nucleus?
Contains all of the body’s genetic information in the form of 46 chromosomes
What is a chromosome?
Long lengths of DNA coiled up
Humans have 46 chromosomes or 23 pairs
What is a gene?
A short section of DNA.
It is a chemical instruction that codes for a particular protein
What is DNA?
Deoxyribo-Nucleic Acid
A long list of instructions on how to put an organism together and make it work
Describe the structure of a DNA molecule.
- Two strands coil together in a double helical shape
- Strands are held together by bases (special chemicals)
- The bases are paired and they will always pair up in the same way: A-T and C-G (complementary base pairing)
What are the four bases in a DNA molecule and which pair with which?
Adenosine
Thymine
Guanine
Cytosine
Adenosine + Thymine
Cytosine + Guanine
What is DNA’s role in a cell?
Controls the production of proteins (protein synthesis)
How does a gene decide which protein is made?
The order of the bases in a gene decides the order of the amino acids
What is a codon?
A sequence of three bases in a gene. Codes for one amino acid
How many amino acid combinations are possible from one gene?
64
4 x 4 x 4
How many amino acids can be made?
20
Therefore some codons form the same amino acid
How many amino acids can be made?
20
Therefore some codons form the same amino acid
What are the two stages of protein synthesis?
Transcription
Translation
Where does protein synthesis occur?
In the nucleus (transcription) and in ribosomes (translation)
What is mRNA and why is it needed?
Messenger RNA
DNA can’t leave the nucleus because it’s too big, so mRNA transfers the gene data
What are the four bases in mRNA and which pair with which?
Adenosine
Uracil
Guanine
Cytosine
Adenosine - Uracil
Guanine - Cytosine
Thymine is replaced with Uracil
What is RNA-polymerase?
The enzyme that joins together the base sequences to form mRNA
How does transcription work?
- RNA-polymerase binds to a region of non-coding DNA
- The two DNA strands unzip and the RNA polymerase moves along one of the strands of DNA
- It uses the coding DNA in the gene as a template to make the mRNA
- Once made, the mRNA moves out of the nucleus and joins with a ribosome in the cytoplasm
How does translation work?
- Amino acids are brought to the ribosome by tRNA (t = transfer)
- The order which the amino acids are brought to the ribosome matches the order of the codons in the mRNA
- The anti-codon on the tRNA is complementary to the codon on the amino acid.
- The pairing between codon and anti-codon makes sure that the amino acids are in the right order
- The amino acids are joined together by the ribosome, making a protein
What is the definition of asexual reproduction?
Reproduction involving one parent. The offspring have identical genes to the parent so there’s no variation between parent and offspring
What is mitosis?
When a cell reproduces by splitting itself in half to form two cells with identical sets of chromosomes
What are the steps of mitsosis?
- Chromosomes in nucleus are copied (one copy for each new cell -> forms X-shaped chromosome)
- Chromosomes line up at centre of cell and cell fibres pull them apart
- Membranes form around each of the new set of chromosomes (become nuclei) and cytoplasm divides
- Two genetically identical daughter cells are made
What is the definition of sexual reproduction?
The fusion of male and female gametes (haploid cells). Because there are two parents, the offspring contain a mixture of their parents’ genes
What is meiosis?
Produces four haploid cells whose chromosomes are not identical.
Two divisions occur. The first is like mitosis, the second is different
What are the steps of meiosis?
- Chromosomes in nucleus are copied (one copy for each new cell -> forms X-shaped chromosome)
- The chromosomes line up in pairs in the centre of the cell. Each pair will have a chromosome each from the mother and father
- 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
- In the second division, the chromosomes line up in the centre of the cell and the arms are pulled apart
- Four haploid gametes that are all genetically different. Each gamete only have a single set of chromosomes
What are alleles?
Different variations of the same gene
What is your genotype?
The alleles that you have
What is your phenotype?
The physical characteristics the alleles produce
What alleles can you have if you’re homozygous?
Two alleles of the same type for that gene e.g. AA or aa
What alleles can you have if you’re heterozygous?
Two different alleles for that gene e.g. Aa
What is a codominant allele?
When neither allele is recessive, so you show characteristics from both alleles.
E.g. blood group AB
What is a mutation?
A rare, random change in an organism’s DNA that can be inherited
What can increase the chance of a mutation?
Ionising radiation e.g. X-rays, gamma rays, UV rays
Chemicals called mutagens (e.g. tobacco smoke)
How can bacteria evolve to become antibiotic resistant?
- Bacteria develop random mutations in their DNA which mean they’re less affected by that antibiotic
- This newly-resistant bacteria lives for longer and reproduces many times
- This leads to the allele for resistance being passed on to most of its offspring
