Inheritance Flashcards
Describe meiosis.
After interphase, Homologous chromosomes ( that carry the same genes) pair up.
meiosis 1: these sets of homologous chromosomes, then separate into two daughters cells.
meiosis 2: the sister chromatids, from the daughter cell, move apart from each other, to form a new pair of daughter cells.
the result is 4 daughter cells, each with half the number of chromosomes of the parent cell.
Identify the differences between meiosis and mitosis.
- Meiosis involves 2 divisions, whereas mitosis only involves one.
- mitosis produces two genetically identical cells, whereas meiosis produces 4 genetically different cells.
- After mitosis, the daughter cell contains the same number of chromosomes as parent cell, whereas in meiosis, they only contain half.
what are all the 3 events through which meiosis produces genetic variation?
Crossing over, independent segregation, mutation.
describe how genetic variation may occur, as a result of crossing over.
Takes place during meiosis 1.
The homologous chromosomes are close enough together, for the chromatids of each pair to twist around each other.
Portions of each chromatid, then exchange with the other homologous partner.
This results in a new allele combination.
describe how genetic variation may occur as a result of independent segregation.
Also takes place during meiosis 1.
When homologous pairs line up, they do so at random.
This randomises the chromosomes that end up in each daughter cell
describe how genetic variation may occur as a result of mutation.
Mat arise through spontaneous mutations.
For example, during mitosis 1, a homologous pair of chromosomes, may not separate.
This results in two gametes with one extra chromosome, and two gametes missing one chromosome.
This is known an non-disjunction.
what’s one other way, apart from meiosis, in which genetic variation may occur?
during fertilisation, any two gametes, may randomly combine, thus producing a new allele.
What is genetic diversity?
number of different alleles of genes in a population.
How can we see genetic diversity?
Through the phenotype present in a population.
The higher the genetic diversity of a population, the higher the variation of phenotypes in a population.
What is a phenotype?
expression of the genotype, and its interactions with the environment.
Define natural selection.
When a new allele, arising from a random mutation, leads to a phenotype in the population, that has a higher reproductive success than other phenotypes, and over generations, the new allele increases in frequency in that specific population.
what are the two types of natural selection?
stabilising selection and directional selection.
describe stabilising selection.
When it favours the intermediate phenotypes.
Meaning that over generations, it causes the frequency of that phenotype to increase.
describe directional selection.
Favours extreme phenotypes.
meaning that over generations, causes the distribution of alleles in the population, to skew towards the extreme.
