How are chromosomes normally found in the body cells?
In pairs
How do body cells divide?
By mitosis
What do chromosomes contain?
Genetic information
What happens when body cells divide by mitosis?
Copies of the genetic material are made then the cell divides once to form two genetically identical body cells
When does mitosis occur?
In growth or to produce replacement cells
How many chromosomes does a sex cell contain?
Only one
What do cells in reproductive organs (testes and ovaries) divide to form?
Gametes
What is the type of cell division in which a cell divides to from gametes?
Meiosis
What happens when a cell divides to form gametes (meiosis)?
Copies of the genetic material are made then the cell divides twice to form four gametes, each with a single set of chromosomes
What happens when gametes join at fertilisation?
A single body cell with new pairs of chromosomes is formed. A new individual then develops by this cell repeatedly dividing my mitosis
When do animal cells differentiate?
At an early stage
When do plant cells differentiate?
Throughout their life
In animals what is cell division restricted to?
Repair and replacement
Where are stem cells found?
Human embryos and adult bone marrow
What can stem cells do?
Differentiate into many different types of cells, e.g. nerve cells
What do human stem cells have the ability to do?
Develop into any kind of human cell
What could treatment with stem cells be used to help?
Conditions such as paralysis
What are the cells produced by asexual reproduction produced by?
Mitosis from the parent cells
What do cells from asexual reproduction contain?
The same alleles as the parents
Why does sexual reproduction give rise to variation?
Because when gametes fuse, one of each pair of alleles comes from each parent
What are the sex chromosomes for females?
XX
What are the sex chromosomes for males?
XY
How many of the chromosomes in the human body cells contain the genes that determines the sex?
One
Some characteristics are determined by…
A single gene
What are the different forms of genes called?
Alleles
What is a dominant allele?
An allele that controls the development of a characteristic when it is present on only one of the chromosomes
What is the recessive allele?
An allele that controls the development of a characteristic only if the dominant allele is not present
What are chromosomes made up of?
Large molecules of DNA which has a double helix structure
What is a gene?
A small piece of DNA
What does each gene code for?
A particular combination of amino acids which make a specific protein
What does each person have?
Unique DNA (apart from twins)
What can individual DNA be used to do?
Identify individuals in the process of DNA fingerprinting
Some disorders are…
Inherited
What is polydactyly?
Having extra fingers or toes
What is polydactyly caused by>
A dominant allele of a gene and can therefore be passed on by only one parent who has the disorder
What is cystic fibrosis?
A disorder of cell membranes
Cystic fibrosis must be inherited from…
Both parents
Can parents be carriers of the disorder without actually having it themselves?
Yes
What is cystic fibrosis caused by?
A recessive allele of a gene and can therefore be passed on by parents, neither of whom have the disorder
What can embryos be to test for these and other genetic disorders?
Screened
