chapter 9- genetic diversity Flashcards
(25 cards)
what is point mutation
a type of gene mutation where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base causing a different amino acid to be coded for
what is silent mutation
a type of gene mutation where a nucleotide in a DNA molecule is substituted by another nucleotide with a different base however due to the degenerate nature of the genetic code the same amino acid is still coded for
what is frameshift mutation
a mutation caused by the addition of deletion of a nucleotide causing the triplets in a DNA sequence to be read differently cause each have been shifted, causing different amino acids to be coded for
what are chromosome mutations
changes in the structure or number of whole chromosomes
when do changes in whole sets of chromosomes occur (polyploidy)
when organisms have three or more sets of chromosomes rather than the usual 2,
when do changes in the number of individual chromosomes occur (non-disjunction)
when individual homologous pairs of chromosomes fail to separate during meiosis, usually resulting in a gamete with one more or one fewer chromosome, causing the offspring from fertilisation to have more or fewer chromosomes
what is a homologous chromosomes
a pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features
what is a chromatid
one of the two strands of a chromosome that are joined together by a single centromere prior to cell division
what is loci
the position of a gene on a chromosome/ DNA molecule
what is an allele
one of a number of alternative forms of a gene. for example, the gene for the shape of pea seeds has two alleles: one for round and one for wrinkled
what is a centromere
structure in a chromosome that holds together the two chromatids and breaks down during DNA replication
what is a histone
proteins which together with DNA, make up the chromosomes of eukaryotic cells
what are haploid cells
cells containing half the number of “normal” chromosomes (gametes)
what are bivalents
the pairs produced when homologous chromosomes pair up before interphase
what are the steps in meiosis
- DNA unravels and condenses to make two sister chromatids joined in three center by a centromere (interphase)
- meiosis 1- the chromosomes are arranged into homologous pairs which are then separated halving the number of chromosomes
- 2 cells are produced each containing a single set of chromosomes
- meiosis 2- the pairs of sister chromatids that make up each chromosome, separate
- 4 haploid cells are produced which are all genetically different from eachother and the parent cell
what is crossing over in meiosis
crossing over is when homologous pairs of chromosomes come together and pair up. as they do this, the chromatids twist causing some of the parts of the chromatids to swap over. the chromosomes where this has happened produce different shapes and leads to the chromatid having the same genes but could now have different combinations of alleles leading to genetic variation in the offspring
what is independent segregation in meiosis
independent segregation is when chromosomes align randomly causing them to separate randomly. this means that each gamete receives a random assortment of maternal and paternal chromosomes
what is non-disjunction in meiosis
non-disjunction is when homologous chromosomes or sister chromosomes do not separate and both members of a pair move to the same pole of the cell. this results in one gamete receiving an extra chromosome whilst the other gamete lacks that chromosome
what is genetic diversity
the total number of different alleles in a population
what is population
a group of individuals of the same species that live in the same place and can interbreed
what does an advantageous allele depend on
the environmental conditions at any one time
what is directional selection
when environment conditions change, causing the phenotypes best suited to vary in one direction from the mean. resulting in the overall change of characteristics in a population
what is stabilising election
when the environmental conditions remain stable, meaning the phenotypes closest to the mean are favoured so the characteristics of a population are preserved
what are the three different types of adaptation
- Anatomical (e.g shorter ears and thicker fur)
-Physiological (e.g oxidising of fat rather than carbohydrate)
-Behavioral (e.g autumn migration of swallows)
