Chapter 9 Flashcards
Define genetic mutation
A change in base sequence of chromosomes
What are mutagenic agents? - give 2 examples
Agents that increase the amount of genetic mutation that occurs
Carcinogens
Radiation
What are the 2 types of gene mutation?
Deletion
Substitution
Why might a gene mutation not affect a protein?
Because the genetic code is degenerate a substitution might not cause a change in amino acid because some amino acids are coded for by more than 1 triplet so it is possible the amino acid will remain the same
Define chromosome mutations
Changes in the structure or number of whole chromosomes
What is Polyploidy?
A condition in which organsims have 3 or more whole sets of chromosomes rather than 2
What is non disjunction?
A conditional where there is a change in the number of individual chromosomes where gametes have 1 more or less chromosomes than they should and therefore the cells have 1 more or less chromosomes than they should
Define substitution
A type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide thay has a different base
Define deletion
A generic mutation that occurs when a nucleotide is lost from the normal sequence of DNA
Why does deletion cause such an impact?
Because all triplets following the deletion will be impacted because the sequence of bases is read in groups of 3 bases
What is meiosis used to make?
Gametes only
Are cells made by meiosis haploid or diploid?
Haploid
How many daughter cells are produced by meiosis?
4
Does meiosis make genetically identical or genetically diverse cells?
Genetically diverse
Meiosis can be described as a source of
Variation
What stages are involved in meioisis?
Replication of genetic information in interphase Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
What happens in prophase 1?
Chromosomes condense and are seen as 2 chromatids
The maternal and paternal chromosomes come together to form a homologous pair
Crossing over occurs
The nucleolus disappears and the nuclear envelope breaks down
What happens in metaphase 1?
The homologous pairs of chromosomes line up on the equator of the spindle
Independent segregation is set up
What happens in anaphase 1?
Independent segregation occues
The homologous chromosomes (1 from each bivalent) separate to each pole
Each pole receives a haploid number of chromosomes (2cells)
What happens at telophase 1?
The chromsomes arrive at each pole 23 chromosomes at each
Temporarily the nuclear envelope forms again and cytokinesis occurs to make 2 cells
What happens at prophase 2?
The nuclear envelope breaks down and new spindle fibres develope
What happens at metaphase 2?
ChromoSOMES line up on the equator of the spindle fibre at the centromere and independent segregation is set up
What happens at anaphase 2?
The centromeres divide and the chromATIDS are we pulled apart as separate pieces
What happens at telophase 2?
The chromATIDS arrive at poles and lengthen to become indistinct
The nuclear envelope reforms
The spindle disappears
Cytokinesis occurs to make 4 haploid cells with 23 chromosomes each
What are the 4 sources of variation in meiosis and fertilisation?
Crossing over
Independent segregation
Mutations
Random fertilisation
Define gametes
A mature haploid cell which is able to unite with another of the opposite sex to form a zygote
Define homologous pair
A pair of chromosomes
1 maternal and 1 paternal that have the same gene loci and therefore determine the same features
Define crossing over
The process whereby a chromatid breaks during meiosis and rejoins to the a chromatid of the homologous pair so their alleles are exchanged
Define independent segregation
Formation of random combinations of chromosomes in meiosis
How do you calculate the number of possible chromosome pairs formed during independent segregation?
2 to the power of n
Define genetic diversity
The number of different alleles of genes in a population
Define species
A group if organisms with similar characteristics capable of interbreeding to produce fertile offspring
Define population
A group of individuals of the same species in a habitat
Explain the process of natural selection
- random mutation or other sources of variation lead to new alleles which can cause selective advantage in the individual
- this leads to increased rates of survival in the individuals
- these individuals are more likely to successfully reproduce
- this passes the advantageous allele on to the next generation
- overtime the FREQUENCY OF THE ADVANTAGEOUS ALLELE INCREASES and the non-advantageous one decreases
all organisms produce more offspring than ____ ___ _____ by the supply of food, light and space
can be supported
despite overproduction of offspring most populations remain ______ . this suggests that there is ______ between members of a species
constant
competition
within any population there is a wide variety of ______ in a gene _____
alleles
pool
some organisms contain _____ that help them to _____ and ______. these organisms are more likely to pass on their _______ _____ to their offspring
alleles
survive and reproduce
advantageous alleles
over time the ______ of the advantageous allele will ______ in a population and the non-advantageous allele will ______ in _____
frequency
increase
decrease
frequency
define selection
the process by which organisms that are better adapted to their environment tend to survive and reproduce while those that are less well adapted tend not to
what are most characteristics described as?
polygenic (influenced by more than 1 gene)
define directional selection
selection that favours an extreme phenotype over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.
give an example of directional selection
giraffes growing long necks
when does directional selection occur? why?
when there is a change in the environment b/c the best adapted organisms survive and reproduce passing on the extreme alleles to their offspring so the next generation will show phenotypes that has shifted towards the extreme phenotype
explain how antibiotic resistance of bacteria shows directional selection occuring
- a spontaneous random mutation occurs in the allele of the bacterium and enabled it to make a new protein that was an enzyme
- this enzyme was able to break down the antibiotic
- the bacterium happened to be in a situation in which it was exposed to the antibiotic
- the bacterium broke down the antibiotic so it survived but the rest died
- there was no competition so the bacteria survived and reproduced by binary fission
- the offspring inherited the ability to break down the antibiotic and there for the frequency of the allele increased in the population ad the normal distribution shifted to the direction of having greater resistance
directional selection results in the _____ at one extreme being ____ for and the other extreme being ____ agains
phenotypes
selected
selected
define stabilising selection
Stabilizing selection is any selective force or forces which push a population toward the average, or median trait.
when does stabilising selection occur
when there is a stable environment
give an example of stabilising selection
babies birth weight
must be in the middle because if too high than there will be birthing complications and if too low the baby will be at risk once born
