17: Inheritance & 18: Variation Flashcards
Describe inheritance
The transmission of genetic information from generation to generation
Define a chromosone
A thread-like structure of DNA, carrying genetic information in the form of genes
Define a gene
A length of DNA that codes for protein
Define an allele
A version of a gene
Describe the inheritance of sex in humans
Mom has XX
Dad has XY & has the role in determining what the sex of the child is as the only has a Y chromosone
Explain the sequence of bases in a gene
Its the genetic code for putting together amino acids in the correct order to make a specific protein
Explain the role of DNA
It controls cell function by controlling the production of proteins (some are enzymes), antibodies and receptors for neurotransmitters
How is a protein made?
- gene coding for the protein remains in the nucleus
- mRNA molecules carry a copy of the gene to the cytoplasm
- mRNA passes through ribosomes
- ribosome assembles amino acids into protein molecules
- specific order of amino acids is determined by the sequence of bases in mRNA
Explain the role of body cells
All body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needes
Define a haploid nucleus
A nucleus containing a single set of unpaired chromosomes (e.g. in gametes)
Define a diploid nucleus
A nucleus containing two sets of chromosomes (e.g. in body cells)
Describe a diploid cell
A pair of each type of chromosomes
In a human diploid cells, there are 23 pairs
Define mitosis
A nuclear division giving rise to genetically identical cells
State the roll of mitosis
In growth, repair of damaged tissues, replacement of cells & asexual reproduction
When does exact duplication of chromosomes occurs?
BEFORE mitosis
What happens during mitosis?
Copies of chromosomes separate, maintaining the chromosome number
Describe stem cells
Unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions
Define meiosis
- A nuclear division giving rise to cells that are genetically different
- A reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells
How does meiosis produce variation?
By forming new combinations of maternal and paternal chromosomes every time a gamete is made
= Gametes fuse randomly at fertilisation, each offspring will be different from any others
Define a genotype
As the genetic make-up of an organism in terms of the alleles present
Define a phenotype
As the observable features of an organism
Define homozygous
Having 2 identical alleles of a particular gene
- 2 identical homozygous individuals that breed together will be pure-breeding
Define heterozygous
Having two different alleles of a particular gene
- A heterozygous individual will NOT be pure-breeding
Define dominant
An allele that is expressed IF present
Define recessive
An allele that is only expressed when there is no dominant allele of the gene present
Define a sex-linked characteristic
A characteristic in which the gene responsible is located on a sex chromosome and that this makes it more common in one sex than in the other
What is colour blindness?
An example of sex linkage
Define variation?
Differences between individuals of the same specifies
What is phenotypic variation?
The difference in features between individuals of the same species (e.g. dyed hair, scratches on legs)
What is genetic variation?
Differences in genes, which is genetic variation (e.g. eye colour)
What is continuous variation?
A range of phenotypes between 2 extremes, e.g. height in humans
What is discontinuous variation?
Results in a LIMITED number of phenotypes with no intermediates, e.g. tongue rolling
- mostly called by genes alone (e.g. A, B, AB & O blood groups in humans)
Define mutation
A genetic change
- the way in which new alleles are formed
Define gene mutation
A change in the base sequence of DNA
What increases the rate of mutation?
Ionising radiation & same chemicals
Describe the symptoms of sickle-cell anaemia
- shortness of breath
- headache or dizziness
- extreme tiredness.
- weakness
- yellowish skin color (jaundice)
How does a change in the base sequence of the gene for haemoglobin results in abnormal haemoglobin & sickle-shaped red blood cells?
The mutation causes haemoglobin molecules to stick together, creating sickle-shaped red blood cells
What do people who are heterozygous for sickle-cell allele have a resistance to ?
Explain the distribution of the sickle-cell allele in human populations
Define an adaptive feature
An inherited feature that helps an organism to survive and reproduce in its environment and increases its fitness
Define fitness
The probability of an organism surviving & reproducing in the environment in which it is found
Explain the adaptive features of hydrophytes and xerophytes to their features
Describe natural selection
Describe selective breeding
Describe evolution
The change in adaptive features of a population over time as the result of natural selection
Define the process of adaptation
The process resulting from natural selection, by which populations become more suited to their environment over many generations
Describe the development of strains of antibiotic resistance bacteria
An example of evolution by natural selection
State differences between natural & artificial selection
