Inheritance! Flashcards
What are alleles? (2)
- Genes that exist in alternative forms
- They lead to differences in inherited characteristics
What is the genome?
- All of the genetic material found in an organism
What does dominant mean?
- An allele that is always expressed
What does recessive mean?
- An allele which is only expressed if not in conjunction with a dominant allele
What does homozygous mean?
- Containing two of the same alleles
What does heterozygous mean?
- Containing two different alleles
What is a phenotype?
- The physical feature that results from the genotype
What is a genotype?
- The two alleles that are present for a particular feature
What is codominance?
- When both alleles contribute to the phenotype
What is monohybrid inheritance?
- The inheritance of one particular trait
What are monohybrid crosses?
- Genetic crosses of single gene combinations
(expected to know how to predict probabilities of outcomes)
Most phenotypic features are…
the result of polygenic (multiple genes) inheritance rather than single genes
XX chromosome
female
XY chromosome
male
There is a genetic variation in offspring because of…
random fertilisation
What is the diploid number of chromosomes in human cells?
46
What is the haploid number of chromosomes in human cells?
23
How does variation arise? (3)
- Environmental: e.g. sunlight on skin colour, amount of food available
- Genetic: e.g. maximum height is determined by its genes
- Both! e.g. if there is a shortage of nutrients in the environment, the genetic potential may not be reached
How does genetic variation arise? (3)
- Meiosis
- Mutations
- Fertilisation in sexual reproduction: random and new combination of alleles
What are mutations? (4)
- Rare, random change
- When DNA is replicating and mistakes are made, so the sequences of bases in a gene is altered
- Can be harmful, neutral, or beneficial
- It is then passed down to other generations
What can affect the rate at which mutations occur? (2)
- Increased by mutagens
- e.g. ionising radiation (UV light, X-rays, gamma rays), chemicals (e.g. from tar in cigarettes)
What is natural selection?
- A factor in the environment that determines which form a species will survive to reproduce
6 mark Q on natural selection acronym
- my very angry sister regina george growls elegantly
- mutation > variation > (better) adaptation (because of selective pressure) > survival > reproduction > genes > generation > evolution
What is mitosis?
- When a cell divides to produce 2 identical sets cells
How does mitosis work in humans? (2)
- Nuclei must undergo replication before the process begins
- To divide a diploid cell by mitosis and produce two diploid cells with identical sets of chromosomes
When does mitosis occur?
- Growth, repair, cloning and asexual reproduction
- e.g. to replace dead skin cells, cancer cells
What is cell differentiation? (2)
- Taking place during embryonic development
- Cells become specialised to carry out a particular function
What are stem cells? (2)
- Has the ability to divide by mitosis
- Remains undifferentiated
Where are stem cells found? (2)
- In the developing embryo (can differentiate into any cell type)
- Adult tissues such as skin/bone marrow (can only become specific types)
What are the advantages of embryonic stem cells? (2)
- Can differentiate into any type of cell in the body
- Can be obtained from spare embryos from IVF (that would otherwise be allowed to perish)
What are the advantages of adult stem cells? (3)
- Removal of cells does not harm the individual
- Cells are easier to control as they are partly differentiated (less likely to cause tumours)
- Fully compatible if derived from the same person
What are the disadvantages of embryonic stem cells? (4)
- Destroys a potential life
- Reliant on women donating their eggs
- May not be fully compatible (not genetically identical)
- Different to differentiate into correct cell types, could form tumours if not done properly
What is meiosis? (3)
- When a cell divides to produce 4 cells with non-identical sets of chromosomes
- Produces cells with half the number of chromosomes (haploid)
- Results in the formation of genetically different haploid gametes (sex cells)
What are the disadvantages of adult stem cells? (2)
- Difficult to obtain and there is a limited quality, it could also cause considerable tissue damage
- Can only differentiate into a limited number of different cell types
What is the correct sequence for protein synthesis?
mRNA -> transcription -> tRNA -> translation
What does the nucleus of a cell contain?
- Chromosomes on which genes are located
What are genes?
- A section of DNA that codes for a specific protein
Describe a DNA molecule
- Two strands coiled to form a double helix
- Base pairs: cytosine and guanine, adenine and thymine
What are the differences between DNA and RNA? (3)
- DNA is a double helix whereas RNA is single stranded
- DNA contains deoxyribose, while RNA contains ribose
- RNA contains the base uracil and lacks thymine
What is a codon? (2)
- 3 bases that code for an amino acid
- Found in both DNA and RNA
What is an anticodon? (2)
- Responds to a complementary codon on mRNA
- Found in tRNA
What are polypeptides?
- Chains of amino acids that join with others to form proteins
Where does protein synthesis take place?
- At the ribosomes in the cytoplasm (therefore genetic code must be copied and transferred out of the nucleus)
How many different amino acids are there?
20
What determines the final shape of the protein?
- The sequence of amino acids
What is transcription?
- When a cell makes a polypeptide, it makes a mRNA copy of the DNA sequence
Describe transcription (3)
- Two strands of the DNA double helix are separated
- One is used as a template and the RNA bases are lined up in order using complementary base pairing
- Once transcribed, the mRNA molecule leaves the DNA and passes out of the nucleus to the cytoplasm
What is used instead of thymine in RNA?
- Uracil
What is translation?
- Assembling the amino acids in the correct order following the sequence of bases on mRNA
Describe protein translation (6)
- mRNA travels out of the nucleus and attaches to a ribosome
- Every three bases on the mRNA codes for one amino acid
- Amino acids are carried to the ribosome by a tRNA molecule
- tRNA has anticodons which can match up with the complementary bases on the mRNA
- Ribosome forms bonds between amino acids
- Polypeptide chain is formed (then joins up with others to form a protein)
Describe the differences between protein translation and protein transcription!!!
