Genetic Diversity: Mutations + Meiosis Flashcards
What do gene mutations involve?
- a change in base sequence of chromosomes
How do gene mutations arise?
- spontaneously, during DNA replication + include base deletion + base substitution
Why don’t all base substitutions cause a change in sequence of encoded AAs?
- bc of degenerate nature of genetic code
What can mutagenic agents do?
- inc rate of gene mutation
How do mutations in NO° of chromosomes arise?
- spontaneously, by chromosome non-disjunction during meiosis
What is chromosome non-disjunction?
- when chromosomes or chromatids don’t split equally during anaphase
- can occur in 2 forms: polyploidy or aneuploidy
What is polyploidy?
- changes in whole sets of chromosomes + occur when organisms have 3 or more sets of chromosomes rather than 2
- mainly occurs in plants
What is aneuploidy?
- changes in NO° of individual chromosomes + occurs when individual homologous pairs of chromosomes fail to separate during meiosis
- results in a gamete having 1 more or fewer chromosome
- if this gamete is fertilised w a gamete w a normal NO° of chromosomes, zygote will have more or fewer chromosomes than normal, in all body cells
What does meiosis produce?
- involves 2 nuclear divisions, so produces 4 haploid daughter cells, that are genetically diff from each other, from 1 diploid parent cell
What 2 mechanisms in meiosis introduce genetic variation among daughter cells?
- independent segregation of homologous chromosomes
- crossing over between homologous chromosomes
Describe how independent segregation of homologous chromosomes introduces genetic variation among daughter cells.
- in meiosis 1, homologous pairs of chromosomes line up opposite each other at equator of cell
- it’s random which side of equator paternal + maternal chromosomes from each homologous pair lie
- pairs are separated, so 1 of each homologous pair ends up in daughter cell
- this creates a large NO° of possible combinations of chromosomes in daughter cells produced
How do you calculate the NO° of possible diff combinations of chromosomes in a daughter cell produced, w/o crossing over?
- 2^n
- n = NO° of homologous chromosome pairs
Describe how crossing over between homologous chromosomes introduces genetic variation among daughter cells.
- when homologous pairs line up opposite each other at equator in meiosis 1, parts of chromatids can become twisted around each other
- this puts tension of chromatids, causing pairs of chromatid to break, which recombine w another chromatid, resulting in new combinations of alleles
Describe how meiosis differs from mitosis.
meiosis:
- 2 nuclear division, so produces 4 daughter cells
- produces haploid cells (1 set of chromosomes)
- creates genetic variation
mitosis:
- 1 nuclear division, so produced 2 daughter cells
- produces diploid cells (2 sets of chromosomes)
- creates genetically identical cells
How do you identify meiosis in a life cycle?
- involves a diploid (2n) parent cell dividing, to become a haploid (n) cell
How is genetic variation within a species further inc?
- random fertilisation of haploid gametes
