Studied by 3 people
What are gametes?
Sex cells → sperm/eggs in humans or pollen/eggs in plants
Why does asexual reproduction produce genetically identical clones?
There is no fusion of gametes so genetic material dosen't mix
What process is involved in asexual reproduction?
Mitosis
What is fertilisation
The fusion of the nucleus of male and female gametes to form a zygote
What process is involved in sexual reproduction?
Mitosis AND meiosis
How are gametes formed?
During meiosis
What are the stages of meiosis?
DNA duplicate
The chromosomes line up at the equator in pairs
The cell undergoes meiosis 1 → the pairs of chromosomes are pulled apart
Some of the mother's and some of the father's chromosomes go into new cells → genetic variation
Chromosomes line up at the equator in both cells
The cell undergoes meiosis 2 → chromosomes are pulled apart
4 gametes are formed → each have 23 chromosomes
Where does meiosis occur?
In the testes and ovaries
How many chromosomes do we have?
46 → 23 pairs
Define zygote
A fertilised egg cell
What are the advantages of sexual reproduction?
Variation in offspring
Species can adapt to new environments
Disease is less likely to affect all individuals in a population
What are the advantages of asexual reproduction?
Population can increase rapidly when the conditions are favourable
Only one parent is needed
More time /energy efficient as you don't need a mate
Faster than sexual reproduction
What are the disadvantages to sexual reproduction?
Time and energy are needed to find a mate
Not possible for an isolated individual (incells)
What are the disadvantages of asexual reproduction
no variation in a population
Species may only be suited to one habitat
Disease may affect all the individuals in a population
What is the structure of DNA?
A polymer made from 4 different nucleotides, shaped like a double helix
What does a nucleotide consist of?
Sugar
Phosphate group
1/4 bases
How does each base complimentary pair with eachother?
C and G
ConGregATe
A and T
Define genetic code
The code formed by the order of the bases in DNA that determines an organism's characteristics
What are chromosomes?
Long threads of DNA made up of many genes
Define gene
A small section of DNA in a chromosome
What do genes do?
They code for a particular sequence of amino acids to make a specific protein
How do malarial parasites reproduce?
Asexually in a human host but sexually in the mosquito
How do fungi reproduce?
Asexually by spores but also sexually to give variation
Define genome
The entire genetic material of an organism
How has the study of the human genome improved medicine?
We can:
Search for genes linked to different types of diseases
Understand inherited disorders and their treatments
Trace human migration patterns
What is a triplet code?
A sequence of 3 bases which codes for a particular amino acid
Define protein synthesis
The production of proteins from amino acids
What is mRNA?
The short section of DNA needed to form a protein
Define mutation
A change in a gene or chromosome
name the different types of mutations
Insertion
Deletion
Substitution
Inversion
What happens during substitution?
One base takes the place of another → different amino acid will be synthesised
What happens during insertion?
An extra base will be added
What happens during deletion?
A base is removed
What happens during inversion?
The order of the bases change
What can mutations of DNA do?
Change the activity of a protein
Change the phenotype → genetic diseases
Define alleles
Different versions of the same gene
What is the difference between genotypes and phenotypes?
Phenotypes → physical characteristics
Genotypes → The allele which gives an organism their characteristics
What are the sex chromosmes for males?
XY chromosome
What are the sex chromosomes for females?
XX chromosomes
What does cystic fibrosis affecr?
Lungs
Digestive system
What happens to the lungs of a patient with cystic fibrosis?
They become clogged with thick, sticky mucus because too much is produced which causes respiratory problems as they become very damaged
What causes cystic fibrosis?
2 faulty recessive alleles → inherited disorder
What is the condition called which causes a person to have extra fingers or toes?
Polydactyly
What causes polydactyly?
A dominant allele → inherited disease
What is the difference between a recessive and dominant allele?
Recessive → both alleles must be present to express the trait → weaker
Dominant → Only one allele is needed to show the trait → stronger
How can genetic disorders be screened?
PGD → used when genetic disorders are linked to the baby's sex
CVS → A sample taken out of the placenta 10-12 weeks into the pregnancy
Amniocentesis → testing amniotic fluid
What are the problems with genetic testing?
Not available for every inherited disorder
Unreliable → false positive/negatives
