4B: Diversity and Selection Flashcards
What is a Diploid cell?
a cell that has the normal number of chromosomes for the organism, 2n
What is a Haploid Cell?
a cell that has half the normal number of chromosomes for the organism, n
What is fertilisation?
when the sperm fuses with the egg
Give examples of Haploid cells
Sperm
Egg
What processes during meiosis can lead to genetic variation?
- Homologous chromosomes pair up / form bivalents
- This can lead to the formation of a chiasma and crossing over can occur
- (Crossing over) results in a new combination of alleles
- Chromosomes can also align randomly
- This is known as independent segregation/assortment
- Which can produce varying combinations of chromosomes (alleles)
Contrast Meiosis and Mitosis
Meiosis:
- produces haploid cells
- cells are genetically different
- produces 4 daughter cells
Mitosis:
- produces diploid cells
- cells are genetically identical
- produces 2 daughter cells
Name 2 types of mutation
Substitution
Deletion
What is Substitution?
one base is substituted with another
What is deletion?
one base is deleted, causing a frame shift
Describe the possible effects of a Substitution Mutation
may not always lead to a change in amino acid sequence because genetic code is degenerate
may cause a different amino acid to be coded for or a stop or start codon
Describe the possible effects of a Deletion Mutation
will always cause a change is amino acid sequence
causes a frame shift
What are Mutagenic Agents?
agents that increase the probability of a mutation occurring
What is Chromosome non-disjuction?
a failure of the chromosomes to separate properly
What is genetic Diversity?
the number of different alleles of genes in a species or population
What is a Genetic Bottleneck?
an event that causes a big reduction in a population
Describe the process of Natural Selection
- Not all individuals are as likely to reproduce as eacother, this is called differential reproductive sucess. Individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes
- This mens that a greater proportuion of the next generation inherits the beneficial allele
- Those individuals will then be more likely to survive, reproduce, and pass on their alleles
- So the frequency of the beneficial allele in the population increases from generation to generation
- Over generations, this leads to evolution as advantagous alleles become more common in the population
What are the 3 types of Adaptation?
Behavioural, Physiological, Anatomical
What is a Behavioural Adaptation?
The ways an organism acts to increase its chance of survival
What is a Physiological Adaptaion?
Processes inside an organism’s body that increase its chance of survival
What are Anatomical Adaptations?
Structural features of an organism’s body that increase its chance of survival
What is Directional Selection?
Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This could be in response to an environmental change.
What is Stabilising Selection?
Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. This occurs when the environment isn’t changing, and reduces the range of possible characteristics
What is Disruptive Selection?
When both extreme traits are favored in an environment
