Genome def.
The entire genetic material of an organism
What is a Gene
A gene is a section of DNA found on a chromosome which codes for a specific protein
Where are chromosomes located
In the nucleus of a cell
What do Chromosomes consist of?
They consist of genes strung together with associated proteins
What does DNA stand for
Deoxyribonucleic acid
How many chromosomes do we have in each cell
46 (23 pairs of two identical chromosomes)
How many chromosomes do gametes (sperm and egg cells) have?
23 single chromosomes
DNA definition
DNA is the molecule that contains the instructions for growth and development of all organisms
What does DNA consist of (structure)
It consists of two strands of DNA wound around each other in a double helix
What are the individual units of DNA called
nucleotides
What are nucleotides
Units of DNA which all contain the same phosphate and deoxyribose sugar, but differ from each other in the base attaches
Four bases
Adenine, Thymine, Cytosine, Guanine
Base pairings
Adenine-Thymine
Cytosine-Guanine
What does RNA stand for
Ribonucleic acid
How is RNA different to DNA
- It contains a single strand of nucleotides
- Has the base uracil
- Contains the sugar ribose
What are nucleotides of RNA
The nucleotides are similar to those of DNA, consisting of a phosphate, a sugar and a base, however the sugar is ribose rather than the deoxyribose found in DNA (
What are the bases found in RNA
Adenine, Uracil, Cytosine, Guanine
What is the function of RNA
The function of RNA is to transfer the code for proteins found in DNA out of the nucleus and carry it to the ribosomes in the cytoplasm which make the proteins
How many types of RNA are involved in the making of proteins
Three types
What is Transcription
TRANSCRIPTION OCCURS IN THE NUCLEUS
Proteins are made by ribosomes with the sequence of amino acids controlled by the sequence of bases contained in DNA
DNA cannot travel out of the nucleus to the ribosomes so the base code is transcribed onto an RNA molecule called messenger RNA (mRNA)
What is translation
mRNA then moves out of the nucleus and attaches to a ribosome
The ribosome ‘reads’ the code on the mRNA in groups of three (known as a codon)
There is a specific triplet of bases in mRNA known as a ‘start codon’ which indicates to the ribosome that following this, the code for amino acids for this protein will begin
Each codon following the start codon codes for a specific amino acid
In this way the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein
As each codon moves into the ribosome to be translated, a second type of RNA called transfer RNA (tRNA) moves in to match its complementary base pairs to the codon on the mRNA
The site on tRNA that matches to the mRNA codon is known as the anticodon
If the anticodon contains three complementary bases to the codon, the tRNA remains in place and the amino acid attached to it at the other end forms a bond with the next amino acid in line
In this way, the chain of amino acids that make up the protein is formed
As each tRNA molecule releases its amino acid after bonding, it exits the ribosome and moves off to pick up another amino acid
The last codon of the mRNA contains a triplet of bases in a sequence known as a ‘stop codon’
This indicates to the ribosome that the amino acid chain is now complete and can be released to fold and form the final structure of the protein
What is an allele
Alleles are variations of the same gene
What are the two types of alleles
Dominant and recessive
What is the physical characteristic of an allele called
phenotype
What is the combination of alleles that control each characteristic called
Genotype
What are homozygous alleles
Two of the same alleles
What are heterozygous alleles
Two different alleles
What is codominance
When some genes have alleles that are equally dominant so are both expressed equally in the phenotype
What does polygenic mean
When characteristics are controlled by more than one gene
What kind of phenotypes do polygenic characteristics have
Phenotypes which show a wide range of combinations
What is an example of polygenic inheritance
Eye colour
What is monohybrid inheritance
The inheritance controlled by a single gene
How do we calculate the probability in monohybrid inheritance
Using a punnett square (Genetic cross diagram)
What are family pedigree diagrams used for
Tracing the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family
Examples of genetic disorders
- Huntington’s disease
- Haemophilia
- Cystic fibrosis
How are males and females represented in a family pedigree chart
Males are represented with a square and females are represented with circles
Female sex chromosomes
XX
Male sex chromosomes
XY
When does mitosis occur
- Growth (production of new cells)
- Repair (to replace dead or damaged cells)
- Asexual reproduction (mitosis produces genetically identical offspring)
What is mitosis
Mitosis is cell devision where a diploid cell copies itself and divides into two identical diploid daughter cells
Describe the process of Mitosis
- Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x – shaped chromosomes)
- Chromosomes line up along the centre of the cell where cell fibres pull them apart
- The cell divides into two; each new cell has a copy of each of the chromosomes
