Inheritance, variation and evolution (2) Flashcards
Where is DNA found in cells
DNA general structure
what is a gene?
How many amino acids code for how many proteins
What is a genome?
-found in the cell nuclei in structures called chromosomes
these come in pairs, 23 pairs in each cell
-DNA is formed of two polymer chains coiled to form a double helix shape
-a gene is a small section of DNA that codes for a specific sequence of amino acids to make a protein (only 20 amino acids are used to make 1000+ proteins)
-The type of protein determines the of cell created
Genome- term for the entire set of genetic material in an organism
Nucleotides and Complementary base pairing
A chain of repeating units that consist of a sugar, phosphate group and a base
The sugar and phosphate groups form a ‘backbone’ to the DNA strands
There are 4 bases (A pairs with T, C pairs with G) which link together on the opposite side of the helix
The order of bases decides the order of amino acids (each amino acid is coded for by a sequence of 3 bases)
Parts of DNA turn genes on or off to decide whether it makes a protein
Protein synthesis
Proteins are made in ribosomes
an mRNA molecule matches to a DNA strand in the nucleus, replacing T with U
the mRNA molecule copies the DNA from the nucleus and returns to the ribosomes
The DNA double helix ‘unzips’ and groups of three bases (triplet code) are copied
Carrier molecules bring the correct amino acids
Enzymes- biological catalysts
Hormones- carry signals around the body to inhibit a response
Structural proteins- strong and strengthened connective tissues
Protein functions (3)
Enzymes- biological catalysts
Hormones- carry signals around the body to inhibit a response
Structural proteins- strong and strengthened connective tissues
Meiosis-
same as mitosis but two daughter cells divide again to halve the number of chromosomes to form four haploid daughter cells
What are mutations: (which has the smallest effect)
Insertions-
Deletions-
Substitutions-
Mutations: a gene randomly changing which affects protein functions (can be inherited)
Insertions- a new base being added randomly
Deletions- a base being removed randomly
Substitutions- a base being replaced randomly (smallest effect as there is still a triplet code)
Sexual v Asexual reproduction
sexual- fusion of gametes to create genetically different offspring with genetics from both parents
Causes variation which is a benefit for natural selection
Selective breeding
Asexual- genetically identical clones that are easily and rapidly produced
What is an allele?
What are two of the same alleles?
What are two different alleles?
What is a Dominant allele?
What is a recessive allele?
a version of a gene
Homozygous
Heterozygous
Always expressed, only one allele is needed (Aa, AA)
Only expressed if both alleles are recessive (aa)
-What is this diagram called
x y -What are the percentage chances for each
genotype?
x XX : XY
==========
x XX : XY
Punnet square
50% XX 50% XY
What is genotype and phenotype
genotype- genetic makeup (aa or Aa)
phenotype- expressed characteristics
embryo screening
During IVF, a cell’s genes can be analysed to detect genetic disorders
This is mostly positive, preventing having unhealthy children
However, there are ethical concerns about being biased to ill people
Adult genetic testing
a blood test to observe adult DNA
Antenatal testing
Tests on embryos chromosomes before they’re born for natural pregnancies
What causes Cystic Fibrosis and what does it do
caused by a recessive allele
It causes the body to produce a lot of thick mucus that builds up in the airways and pancreas, making breathing more difficult
What causes Polydactyly and what does it do
Caused by a dominant allele
causes extra fingers and toes
What did Gregor Mendel do
He discovered how pea plants pass on genetic characteristics through generations
Selective breeding
- animals with desired characteristics (high meat content) are bred together
- the offspring inherit those genes
- The offspring are bred together to strengthen the desired characteristics in their offspring
- This can be repeated for generations to create better and better animals
disadvantages- reduction in variation and gene pool, incest
Genetic variation
different genes cause all organisms to look different as genetic information mixes from parents
Environmental variation
Conditions in the environment (more sunlight) cause organisms to look differently (taller plants)
Evolution
Who developed the theory
- a member of the species has a mutation that makes it better suited to the environment
- The organism thrives and reproduces so its offspring have the characteristic
- Over time, the mutation-carrying organisms survive better and the original species become extinct
Charles Darwin
genetic engineering-
examples (3)
genetic engineering- inserting a gene into an organisms genome so that is synthesisis specific proteins to achieve a desired characteristic
- Useful gene is isolated from an organisms genome using enzymes
- inserted into a vector (normally a virus or bacteria plasmid)
- when the vector is introduced to the target organism, the gene is inserted into its cells
bacteria producing insulin
GM crops
Treat inherited diseases
Plant cuttings-
cells from fertilisation of plants can be separated to produce identical offspring
Cloning-
(Ethics)
- nucleus removed from skin cell
- nucleus inserted into an egg cell
- electric shock causes the cell to split and develop
- developing cells are inserted into a surrogate mother
- a clone is born
it’s a controversial topic, as it could be potentially unsafe and is viewed as unethical and unnatural
Fossils:
replacement by minerals-
casts and impressions-
Preservation-
replacement by minerals- bone structures are replaced by minerals as they slowly decay and become surrounded by rock
casts and impressions- formed by being compressed in sediment leaving a cast
Preservation- fossils can be preserved in amber, tar pits, glaciers, peat bogs as microbes can’t decay the organism
