Inheritance, Variation and Evolution Flashcards
Describe the stages in meiosis
Only takes place in the testes and ovaries.
All the chromosomes are copied.
The cell divides into two.
Both of these cells divide one more time forming gametes.
In the gametes, the chromosomes are now single, not paired.
Meiosis has halved the number of chromosomes, and produces four gametes from one cell.
Each of the gametes are genetically different from each other.
Describe the stages in meiosis
Only takes place in the testes and ovaries.
All the chromosomes are copied.
The cell divides into two.
Both of these cells divide one more time forming gametes.
In the gametes, the chromosomes are now single, not paired.
Meiosis has halved the number of chromosomes, and produces four gametes from one cell.
Each of the gametes are genetically different from each other.
What happens to the gametes produced from meiosis?
Gamete from the male and from the female join together- fertilisation.
The cell now has the normal number of chromosomes.
23 chromosome pairs.
After this, the new cell divides by mitosis, producing a clump of identical cells called an embryo.
As embryo develops, the cells differentiate forming different cell types.
Describe the structure of DNA
Consists of two strands. Each strand is a polymer.
The strands wrap around each other to form a double helix.
What is a gene?
A small section of DNA on a chromosome.
Each gene encodes for a specific sequence of amino acids to make a specific protein.
What is the genome?
The entire genetic material of an organism.
Human genome is the entire genetic material that makes a human.
What are the benefits of scientists studying the human genome?
Helps us search for genes that are linked to disease.
It will help us to understand and treat inherited disorders eg cystic fibrosis.
We can trace human migration patterns in the past- so you can discover your ancestry.
What is DNA? (triple)
A polymer of molecules called nucleotides.
Nucleotides are made up of a phosphate group, attached to a sugar molecule. The sugar is attached to a base.
The phosphate group and sugar molecule never change.
4 different bases:
A, C, G, and T.
The DNA strands are complementary.
C-G
A-T.
How many different amino acids are there in humans?
20
What determines the shape of the protein?
The specific order of the amino acids.
The shape of the protein determines its function.
What determines the order of amino acids in a protein?
It is determined by the sequence of bases in the gene for that protein.
How does the cell read the DNA sequence?
Reads the DNA sequence as triplets of bases.
Each triplet encodes for a specific amino acid in the protein.
Explain protein synthesis:
First stage: Transcription (in the nucleus)
- The base sequence of the gene is copied into a complementary template molecule (mRNA).
- mRNA is a single-stranded molecule.
- The mRNA now passes out of the nucleus and into the cytoplasm.
Second stage: Translation (in the cytoplasm)
- The mRNA attaches to a ribosome.
- Amino acids are now brought to the ribosome on carrier molecules (tRNA).
- The ribosome now reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order.
- Once the protein chain is complete, it now folds into its unique shape.
How do changes in the base sequence of DNA (mutations) affect the structure of proteins?
Most of the time:
It does not change the amino acid sequence. This is because different base triplets can sometime encode for the same amino acid. So the mutation had no effect on the protein’s shape or function.
However:
Sometimes the protein has a different amino acid.
This change has altered the shape of the protein. This could have a dramatic effect on the function of the protein e.g. the active site of an enzyme may change shape so it can no longer attach to the substrate.
What is a mutation?
A change to a base.
