DNA and the Genome, Genetic Inheritance, Variation and Evolution (NOT COMPLETE FOR GCSE) Flashcards
What is the genetic material in the nucleus composed of?
- DNA
What is DNA?
a long polymer made of 2 strands twisted into a double helix
What are chromosomes?
- long lengths of DNA tightly coiled
What are genes?
- short sections of DNA
- codes for specific sequence of amino acids
- forms proteins
What can scientists do now that they have sequenced the entire human genome?
- search for genes linked to particular diseases
- understanding and treating inherited disorders
- tracing of past human migration patterns
What is a double helix made out of?
- repeating nucleotides joined together = 2 long strands
- bases attached to each sugar at 90 degrees
- meets in the middle, holds 2 strands together
- 2 strands twisting around each other = double helix
What are nucleotides made of?
- a sugar
- a phosphate group
- a base
What codes for a particular amino acid in a protein?
- 3 bases
- order of every set of 3 bases = a type of amino acid in protein
Where are the instructions to build all of the proteins required in the cell?
DNA in the nucelus
Describe protein synthesis
1) single strand copy of DNA- mRNA made in nucleus
2) moves from nucleus to ribosome
3) carrier molecules bring specific amino acids in right order based on mRNA template
4) forms chain of amino acids (3 bases = 1 amino acid)
5) chain complete = folds into unique shape
6) unique shape = enables protein to do job (enzyme, hormones, forming structures- collagen)
Do all parts of DNA code for proteins?
- No
- non-coding parts can switch genes on and off
- variations = changes in how genes are expressed
How do mutations in coding DNA affect protein synthesis?
- causes shape of protein to be different
- most do not alter function/ appearance (slight alteration)
- few mutations = altered protein, different shape
- enzyme may no longer fit substrate binding site/ structural protein loses its strength
What is a gamete?
a sex cell formed by meiosis
What is an allele?
a variation of a gene
What is a dominant allele?
an allele that only needs one copy to be expressed
What is a recessive allele?
an allele that needs two copies to be expressed
What is homozygous?
having two copies of the same allele for a trait
What is heterozygous?
having two different alleles for a trait
What is a genotype?
the combination of alleles that an organism has
What is phenotype?
The expressed genotype of an organism
What is polydactyly caused by?
a dominant allele
What is cystic fibrosis caused by?
a recessive allele
How many pairs of chomosomes does a human have?
23 pairs
What does embryo screening do?
detects genetic disorders in embryos
Describe natural selection
- mutations occur in populations (common)
- mutations occasionally alters phenotype
- might be more suited to changing conditions
- individual more likely to survive and reproduce
- passes mutation to offspring
What is evolution?
- change in inherited characteristics of a population over time
- through natural selection
- may result in formation of new species
Why does genetic variation occur?
differences of alleles inherited by individuals
Why does environmental variation occur?
if individuals develop in different conditions
Why is there a variation in the population?
mixture of environmental and genetic variation
What does the theory of evolution by natural selection state?
- all species of living things have evolved from simple life forms that first developed three billion years ago
At what point do two populations of the same species become two different species?
- phenotypes so different that they could no logner interbreed to produce fertile offspring
How long have humans been selectively breeding plants and animals?
- thousands of years
- bred food crops from wild plants
- domesticated animals
Describe selective breeding
- choose parents with desired characteristic from population
- bred together
- choose offspring with desired characteristic and breed together
- continues over many generations until all offspring show desired characteristic
How are males chosen for certain characteristics that only females have?
eg milk
choose from male’s female offspring
What can inbreeding lead to?
- some breeds being particularly prone to disease or inherited defects
What are plants selectively bred for?
- food crops with disease resistance
- large or unusual flowers
What are animals selectively bred for?
- produce more meat and milk
- domestic dogs with gentle nature
What are crops genetically modified for?
- add resistance to pests
- increase crop yield
- resistant to herbicides (only kills weeds, not crops)
How was genetic engineering used for production of human insulin?
- gene for human insulin “cut out” from chromosomes of human cells
- added to genome of bacterial cells
- bacteria makes insulin
- done at large industrial scale, collected
- increases supply of human insulin for people with diabetes
How does genetic engineering work?
- enzymes used to “cut out” or isolate required gene
- required gene inserted into vector (viruses/ bacterial plasmids)
- vector inserts gene into cells of target organism
What are the concerns of genetic engineering?
- reduces biodiversity, populations of wild flowers/ insects decreases around GM crops
- unknown long term effects of eating GM crops for humans
What could gene therapy treat?
what are the concerns?
- genetic disorders eg cystic fibrosis
ethical objections to altering human genome
When did Darwin publish his theory of evolution by natural selection?
1859
took a while to be accpeted by scientists
Why was Darwin’s theory only gradually accepted?
- theory challenged idea that God made all of the animals and plants that live on earth
- insufficient evidence at the time to convince many scientists
- mechanism of inheritance and evolution was not known until 50 years after theory was published
What was another theory of evolution and who was it by?
- Jean-Baptiste Lamarck
- changes that occur in organism throughout lifetime could be inherited
not true for vast majority of cases