B13 - Reproduction Flashcards
What is sexual reproduction
Male and female gamete fuse during fertilisation
Offspring are not genetically identical to either parent
2 parents are needed
Mixing of genetic material
What is asexual reproduction
No fusion of gametes
Offspring are genetically identical to parent
Only 1 parent needed
No mixing of genetic material
Advantages of sexual reproduction
produces variation in the offspring
if the environment changes variation gives a survival advantage by natural selection
natural selection can be speeded up by humans in selective breeding to increase food production.
Advantages of asexual reproduction
only one parent needed
more time and energy efficient as do not need to find a mate
faster than sexual reproduction
many identical offspring can be produced when conditions are favourable.
What are gametes
Sex cells
What is meiosis
Meiosis is a type of cell division that produces gametes.
In males, meiosis occurs in the testes.
In females, meiosis occurs in the ovaries.
What happens during meiosis?
DNA replicates (chromosomes double)
the cell divides twice to form four cells (gametes), each with a single set of chromosomes
all gametes are genetically different from each other.
What is a genome
The genome of an organism is the entire genetic material of that organism.
What is the genetic material made of
The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA is a polymer made up of two strands forming a double helix.
The DNA is contained in structures called chromosomes.
A gene is a small section of DNA on a chromosome.
What is the structure of DNA
DNA is double stranded and in the shape of a double helix. Each strand is a polymer made up of repeating units called nucleotide.
How do genes code for proteins
A gene is a section of DNA containing instructions to put amino acids together in a particular order to make a protein
Describe how a protein is synthesised in a cell
Specific genes in the DNA produce a template for the protein, the template has the same sequences of bases that created the amino acids.
The template leaves the nucleus through the pores in the membrane and binds to the surface of a ribosome.
The carrier molecules attach to the specific amino acids and are moved to the template and ribosome.
The amino acids form together to make a specific protein on the template when all the amino acids are present.
The protein then detaches from the carrier molecules and the carrier molecules detach from the template and return to the cytoplasm.
What are mutations
Mutations are changes to the DNA structure. They can result in new forms of genes being made.
Mutations are random but they happen quite often (usually during cell division).
What can happen because of a mutation
Nothing! There isn’t an effect on the expression of the gene or the protein produced
2. There is a useful change - this is important in natural selection (future topic!)
3. A different protein might be coded for which doesn’t function properly, e.g.
The active site of an enzyme might not fit the substrate anymore
A hormone might not be able to attach to receptors on cells
A structural protein might be weakened
4. A mutation in the non-coding part of the DNA might affect how genes are expressed
E.g. genes might be switched off instead of on
What is a gene
A section of DNA that codes for a protein. Some characteristics are controlled by a single gene.
