Meiosis and genetic variation Flashcards
what can mutations be caused by?
-errors in replication
-mutagenic agents (e.g. chemicals, radiation, smoking)
what is the definition of mutation?
any change to the quantity or base sequence of DNA of an organism
what is a gene mutation?
any change to the nucleotide bases or sequence of bases in DNA
what are the 3 types of gene mutation?
-addition (one base added)
-deletion (one base removed)
-substitution (one base swapped for another)
which gene mutations lead to frameshift mutations?
deletion and addition
why are frameshift mutations more harmful?
they cause a shift in all other triplet bases, changing the way other bases are read, causing the mutated protein to be different to the original protein.
why may the protein coded for change in gene mutations?
if the amino acid sequence is altered then the tertiary structure changes, affecting the functioning of the protein
what is a chromosome mutation?
a change in the structure or number of whole chromosomes
what are the 2 forms of chromosome mutation?
-changes in the whole set of chromosomes
-changes in the number of individual chromosomes
what happens when there are changes in the whole set of chromosomes?
this is when an organism has 3 sets of chromosomes instead of 2, called polyploidy (mostly in plants)
what happens when there are changes in the number of individual chromosomes?
this may be due to failure to separate properly in meiosis 1- called nondisjunction and it usually results in the gamete having 1 extra or less chromosome
what is non-disjunction?
when chromosomes fail to separate in meiosis 1, resulting in a gamete having one extra or less chromosome, leading to inherited diseases
what is a disease that is an example of non-disjunction?
down’s syndrome, which is 1 extra chromosome
what does diploid mean?
full set of chromosomes (46)
what does haploid mean?
half the full set of chromosomes (23)
what are gametes?
sex cells
what is a homologous pair of chromosomes?
2 chromosomes in a pair, one maternal, one paternal, with the same genes
what is independent segregation in meiosis 1?
the mechanism by which each chromatid goes into which cell (random)
describe the process of crossing over
when the non-sister chromatids twist around each other at the chiasmata in meiosis 1 and then break to exchange pieces of DNA. this allows new combinations of genetic information to form. they then re-join, forming recombinant chromosomes.
what happens in meiosis 1?
homologous chromosomes pair up and their chromatids wrap around each other. crossing over occurs. by the end of the division, homologous pairs have separated, with one chromosome from each pair going into one of the 2 daughter cells
what happens in meiosis 2?
chromosomes move apart. at the end of the division, 4 haploid daughter cells are formed, genetically different. this leads to adaptations which increase survival chances.
when do you start referring to chromatids as chromosomes?
meiosis 2
what is random fertilisation?
the process of which male gamete fertilises a female gamete being random, creating a specific offspring
how is genetic variation added?
-independent segregation
-crossing over
-random fertilisation
describe independent segregation
during anaphase in meiosis 1, the process by which the chromosomes migrate is random. chromosomes from each pair line up at random and move to either pole, giving many different combinations.
