Genes, chromosomes, cell division and variation Flashcards
What shape is DNA?
Double helix
How many bases are there in DNA?
4
Name the bases in DNA
Adenine, Cytosine, Guanine and Thymine
Which bases pair with each other?
A with T, C with G (complimentary base paring)
What is a gene?
A length of DNA which codes for a protein
What do these proteins control?
Chemical reactions, growth, colouration and all inheritable characteristics
What do chromosomes control?
a SET of characteristics e.g. eye colour, hair colour
What is a chromosome?
Long strands of DNA wound up and compacted to make it smaller
How many pairs of chromosomes do humans have?
23 pairs (46 chromosomes)
What is the name of having two copies of a chromosome?
Diploid
Some organisms contain one copy of each chromosome, what is this called?
Haploid
XX = ??
Female
XY = ??
Male
Name 2 human haploid cells
Egg and sperm
What are the two types of cell division?
Mitosis and meiosis
Explain the process before cell division begins
Chromosomes replicate, making exact copy of themselves, doubles amount of DNA in cell
What is mitosis used for?
Growth, repair and asexual reproduction
What does mitosis produce?
Genetically identical (diploid) daughter cell
What is meiosis used for?
ONLY used for producing gametes (sperm, eggs, pollen - not identical) for sexual reproduction
What is meiosis?
Process by which we make genetically varied cells with half the number of chromosomes
What is variation in offspring produced by?
1) genetic variation in gamete cells produced by meiosis
2) random fertilisation of ova by male gametes
Mitosis vs meiosis: what they produce
- Mitosis: genetically identical daughter cells
- Meiosis: non-identical
Mitosis vs meiosis: number of what they produce
- Mitosis: 2 cells
- Meiosis: 4 cells
Mitosis vs meiosis: division
- Mitosis: 1 divison
- Meiosis: 2 divisions
Mitosis vs meiosis: haploid or diploid in humans?
- Mitosis: diploid
- Meiosis: haploid
Mitosis vs meiosis: number of chromosomes
- Mitosis: keeps same number
- Meiosis: halves number
Mitosis vs meiosis: where it occurs in humans
- Mitosis: throughout human body
- Meiosis: in ovary and testis
Mitosis vs meiosis: where it occurs in plants
- Mitosis: throughout plant
- Meiosis: ovary and anther
Mitosis vs meiosis: sexual or asexual reproduction?
- Mitosis: asexual
- Meiosis: sexual
What is variation?
The difference between individuals
3 causes of variation
Genetic, environmental or combination of both
What is a mutation?
A change in the DNA
Chromosomal mutation?
When a cell gains an extra chromosome or one part of a chromosome is stuck onto another
Sequence mutation?
A change in the sequence by replacing a single base pair with a different pair - changes sequence of amino acids in the encoded protein (effects protein shape)
3 possible outcomes of mutations
Positive, negative and neutral
What are mutagens?
Chemicals which cause more frequent mutations
