Unit 5^ Variation + Selection Flashcards
Where are chromosomes found?
Chromosomes are found in the NUCLEUS
What is a chromosome?
Long lengths of DNA 🧬 coiled up
How many chromosomes does each parent give?
Each parent (sperm+egg) give 23 chromosomes = durin fertilisation the genetic material fuses to form a cell w/ 46 chromosomes
How many chromosomes does a human have?
46 chromosomes
How many pairs of chromosomes are there in every human body cell?
23 pairs of chromosomes in every human body cell
What is a GENE
A gene is a short section of DNA which codes for a specific protein
What are different versions of the same gene called
An ALLELE = different versions of the same gene
What are the 4 nitrogenous bases in DNA
ADENINE + THYMINE
CYTOSINE + GUANINE
What does RNA polymerase do?
It’s an ENZYME involved in joinin up the base sequence to make mRNA
Describe a DNA 🧬 molecule
two strands coiled to form a double helix linked by a series of paired bases : adenine + thymine, guanine +cytosine
Give 3 differences between a DNA molecule and an RNA molecule
- DNA is double helix, whereas RNA is single stranded
- DNA has the sugar deoxyribose, whereas RNA has RIBOSE
- RNA contains base URACIL (U) instead of thymine (T) which is in dna
What’s an allele
Different version of the same gene
How many copies of each gene do humans have?
2 copies
What is meant by the term HOMOZYGOUS
When an individual has two alleles the same (TT)
What is meant by the term HETEROZYGOUS
When an individual has two different alleles (Tt)
Genotype
The combination of alleles for a certain characteristic
Can be either homozygous or heterozygous
Phenotype
The observable characteristics resulting from the genotype
What is meant by the term polygenic inheritance
Characteristics controlled by 2 or more genes working together
Codominance
A pattern of inheritance where
neither allele of a gene is dominant over the other
so that both alleles are expressed in the phenotype
🌺🌼===>🌸
What is a pedigree
A family tree of genetic disorders
Describe what is meant by the term cytokinesis
In mitosis, when after telophase the cytoplasm splits into two genetically identical daughter cells
What is a mutation
A random change in genetic code
What is meant by the term mutagen
Factors that increase the rate of mutation
E.g. carcinogens present in cigarette smoke or gamma radiation
What is meant by the term ‘selective breeding’
When organisms are selectively bred to develop desirable features
Name the 4 steps in the process of selective breeding
🐮 select organisms with desirable characteristics
🐮 breed them w each other
🐮 select best ‘offspring’
🐮 repeat……
Explain why selective breeding is not natural selection
Because in selective breeding the selection pressure is not environmental, it is just human desire
Explain the theory of evolution
Evolution = life began as simple organisms which evolved as a result of random mutations to more complex organism over time
Describe the 5 steps in NATURAL SELECTION
🌱 organisms in a species show variation in characteristics as a result of random mutations
🌱there’s competition for limited resources in the environment
🌱the organism w most suitable characteristics for the environment has best chance of survival
🌱the ‘fittest’ has the best chance of breeding + passing on its genes
🌱over generations the characteristic which increases survival becomes more common + as a result the species becomes better adapted for its enviro
What organism is it the best to see natural selection take place in and why?
BACTERIA or INSECTS
because they reproduce very quickly unlike animals
What do mutations produce
Random change in sequence of bases= genetic variant
What does a DNA codon code for
The sequence codes for an amino acid
What can mutations do to enzymes?
Mutations can cause the very specific active site to change shape, altering the enzymes function
Why do some mutations not take effect on the phenotype
The mutations don’t effect the phenotype SOMETIMES because the mutation has occurred in an unimportant region of DNA or the mutated codon still codes for the same protein
What is meant by the term ‘antibiotic’
Chemicals that kill/ reduce growth of microorganism
BUT DONT WORK ON VIRUSES cos viruses use a host to reproduce
Describe how bacteria become resistant to an antibiotic (4 marks)
Bacteria contains a random mutation in its DNA which gives it resistance to a particular antibiotic
This resistance means it’s better able to survive + reproduce = lots of bacteria inherit resistance to that antibiotic
Bacteria reproduce fast, so resistance is prominent quickly!
Resistant bacteria r no longer effected by antibiotic= antibiotic ineffective
What is a NUCLEOTIDE and what is it made up of
A nucleotide is a DNA monomer and it is made up of
• a phosphate group
• sugar molecule (deoxyribose)
• a nitrogenous base (A,T,C or G)
Explain the process of DNA replication 🧬 🧬🧬🧬🧬🧬🧬🧬🧬🧬🧬
Before a cell is about to divide it must replicate each DNA molecule in the nucleus.
- the polynucleotide strands separate
- each strand acts as a template for an new strand of DNA
- DNA polymerase (enzyme which joins base pairs) puts nucleotides into pairs
- now 2 identical DNA molecules r formed
All genes code for ________
All genes code for PROTEINS
What is a codon
A triplet code which codes for an amino acid
Sequences of codons for all amino acids in a protein is a _____
Sequences of codons for all amino acids in a proteins is a GENE
What is protein synthesis
The making of proteins in 2 stages
What are the 2 types of RNA and what is there function
mRNA (Messenger RNA)
= forms a copy of the DNA code
tRNA (Transfer RNA)
= which carries amino acids to the ribosomes to make the protein
Describe the process of protein synthesis referencing the 2 main stages and the role of mRNA + tRNA
🔮TRANSCRIPTION [in the nucleus]
Proteins r made by ribosomes in cytoplasm but DNA molecules found in nucleus r too big to move out=
•so the DNA info needs to be carried out of nucleus into the ribosomes in the cytoplasm
🔮mRNA carries this info by unzipping the DNA strand, reading it using enzyme(RNA polymerase) + lining up complimentary base pairs (U instead of T tho)
💬TRANSLATION [in the cytoplasm]
Now the mRNA template needs to be decided into a particular protein.
•so the mRNA binds to a ribosome
💬now the tRNA brings amino acids to the ribosome // these amino acids have anticodons which r complimentary to the codon on the template strand
💬each tRNA bonds to a matching mRNA
• which forms an amino acid, it’s repeated until it’s a chain = a PROTEIN= a GENE
Give 3 reasons for selectively breeding animals
🐄 produce more meat, eggs or milk
🐖 produce more offspring
🐏 to be resistant to certain diseases
Give 3 reasons for selectively breeding crops
🌵 resistant to harsh weather
🌴 give higher yields
🌲have a better balance of nutrients (PROtato)
What is artificial insemination
Instead of physically breeding animals together… semen w desirable features is kept + stored and injected into the uterus of a cow w a syringe
Give 2 benefits of Artificial Insemination
🐄🐂 it can be stored + used even after cow dies
🐂🐄 semen from one cow can fertilise many thousands of cows
Explain how animals are CLONED 🐑
Scientists took an ovum (egg cell) + removed its nucleus = ENUCLEATED CELL 🥚
Took cells from mammary gland + cultured in a solution (this mammary gland is the gene we’re copying) 🥛
They then took the mammary gland cell and fused it w the enucleated cell using electric current ⚡️⚡️
They then planted the embryo into uterus of a surrogate sheep 🐑 == dolly born, genetically indentical
What is meant by the term diploid
Diploid number of chromosomes = 46
What is meant by the term haploid
Haploid numbers of chromosomes = 23
What is INTERPHASE and when does it happen in both mitosis+ meiosis
Interphase is right before cell division when DNA replicates
Give 3 genetic factors that cause variation in genes (genes control inherited traits)
- Eye/hair colour
- blood group
- inherited disorders
Give 3 environmental factor that cause variation in genes
- smoking (lung cancer)
- poor diet (stunted growth)
- exposure to excess UV (melanoma)
Recessive
Allele that is not expressed in the phenotype when a dominant allele (of the gene) is present
Dominant
Allele of the gene that is expressed in the phenotype
What is a genome?
The entire DNA of an organism
