TOPIC 6 - INHERITANCE, VARIATION AND EVOLUTION Flashcards
What are chromosomes?
Long molecules of DNA. The normally come in pairs.
What is DNA?
A polymer. It is made up of two strands coiled together in the shape of a double helix.
They are made up of lots of repeating units called nucleotides.
What is a gene?
A gene is a small section of DNA found on a chromosome. Each gene codes for a particular sequence of amino acids which are put together to make a specific protein.
What is a genome?
A genome is a term for the entire set of genetic material in an organism. Scientists have worked out the complete human genome.
Why is understanding the genome important?
It allows scientists to identify genes in the genome that are linked to different types of diseases.
Knowing what genes are linked to inherited genes.
To trace the migration of certain populations.
What is a nucleotide?
One sugar molecule, one phosphate molecule and one base. The sugar and phosphate molecules in the nucleotides form the backbone to DNA strands. The sugar and phosphate molecules alternate. One of four different bases - A, T, C or G - joins to each sugar.
What are the complementary base pairings?
A pairs with T
C pairs with G
What does the order of bases in a gene determine?
The order of amino acids in a protein.
How are amino acids coded for?
By a sequence of three bases in a gene. The amino acids are joined together to make various proteins, depending on the order of the gene’s bases.
What is mRNA?
Gets the code from the DNA to the ribosome. It acts as a messenger between the DNA and the ribosome, and is made by copying the code. The correct amino acids are brought to the ribosome in the correct order by carrier molecules.
What are some of the functions of proteins?
Enzymes - act as a biological catalyst
Hormones - used to carry messages around the body
Structural Proteins - are physically strong.
What is a mutation?
A mutation is a random change in an organisms DNA. They can sometimes be inherited. They change the sequence of the DNA bases in a gene, which produces a genetic variant.
How do mutations occur?
They change the sequence of the DNA bases in a gene, which produces a genetic variant. As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for.
What is an insertion mutation?
Insertions are where a new base is inserted into the DNA base sequence where it shouldn’t be. It changes the way the groups of three bases are ‘read’ which can change the amino acids that they code for. Insertions can change more than one amino acid as they have a knock-on effect on the bases further in the sequence.
What is a deletion mutation?
Deletions are when a random base is deleted from the DNA base sequence. They change the way that base sequences are ‘read’ and have knock-on effects, like insertions.
What is a substitution mutation?
Substitution mutations are when a random base in the DNA base sequence is changed to a different base.
What is sexual reproduction?
Where the genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parents. The mixture of genetic information produces variation in the offspring.
How many chromosomes does a gamete have?
23 gametes. You get 23 from your mother and 23 from your father.
What is asexual reproduction?
There is only one parent so the offspring are genetically identical to that parent. It happens by mitosis. I is called a clone.
Give examples of organisms that reproduce asexually.
Bacteria
What does meiosis do?
Produces cells which have half the normal number of chromosomes (gametes).
What are the stages of meiosis?
The cell duplicates its genetic material, forming two chromosomes. One arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes arrange themselves into pairs.
In the first division in meiosis the chromosome pairs line up in the centre of the cell.
The pairs are then pulled apart so each new cell only has one copy of each chromosome. Some of the father’s and some of the mother’s chromosomes go into each new cell.
In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
What do you get at the end of meiosis?
You get four gametes, each with only a single set of chromosomes in it. Each of the gametes is genetically different from the others because the chromosomes get shuffled up during meiosis and each gamete only gets half of them, at random.
What is the advantage of sexual reproduction?
More variation. This increases the change of a species surviving a change in the environment. They have a survival advantage.
Because species with characteristics that make them better adapted to the environment have a better chance of survival, they are more likely to breed successfully and pass the genes for the characteristic on. This is known as natural selection.
Selective breeding can also be used to speed up natural selection.
What are the advantages of asexual reproduction?
There only needs to be one parent. So, it uses less energy than sexual reproduction, because organisms do not have to find a mate. This makes it faster.
Many identical off spring can be produced in favourable conditions.
Give example of organisms that can reproduce both sexually and asexually.
Malaria is caused by a parasite that is spread by mosquitoes. The parasite reproduces sexually when it is in the mosquito and asexually when it is in the human host.
Species of fungus. They release spores, which can become new fungi when they land in a suitable place. Sexually-produced spores introduce variation and are often produced in response to unfavourable change in the environment.
Lots of species of plant produce seeds sexually, but can also reproduce asexually.
What are alleles?
Different versions of genes.
What does homozygous mean?
When the organism has two alleles for a particular gene.
What does heterozygous mean?
If the two alleles for a particular gene are different
What does dominant mean?
The allele for the characteristics that are shown is called the dominant allele. Capital letter are used for dominant alleles.
What needs to happen for an organism to display a recessive characteristic?
Both its alleles must be recessive.
What needs to happen for an organism to display a dominant characteristic?
It can either have one dominant alleles or two. This is because the dominant allele over rules the recessive one if the organism is heterozygous.
What is your genotype?
The combination of alleles you have.
What is your phenotype?
Your alleles work at a molecular level to determine what characteristics you have - phenotype.
What is cystic fibrosis?
A genetic disorder of the cell membranes. It results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas.
The allele which causes cystic fibrosis is a recessive allele, carried by about one in five people.
What does it mean if you are a carrier of cystic fibrosis?
People with only one copy of the allele will not have the disorder (recessive) - they are known as carriers.
What conditions are required for a child to be born with cystic fibrosis?
For both parents to be carriers or to have the disorder themselves.
What is polydactyly?
A genetic disorder where a baby is born with extra fingers or toes.
The disorder is caused by a dominant allele. (capital). This means that it can be inherited if just one parent carries the defective allele.
