!!!⭐️Genetic Info, Variations And Relationships: Genetic Diversity And Adaptation Flashcards
What is a gene mutation?
Any change to the quantity of bases or base sequence in the DNA
What does the fact the genetic code is degenerate mean for mutations?
That mutations don’t always result in a change in the amino acid sequence of the polypeptide.
What are the 2 types of mutations?
Base substitution and base deletion or insertion
What is base substitution?
Where a base is substituted for another and may result in a change of 1 amino acid because the base sequence is changed
What is base deletion or insertion?
Where a base is deleted or inserted causing the number of bases to change
Which type of mutation is more likely to produce a dysfunctional protein?
Base deletion or insertion is more likely to produce a dysfunctional protein than base substitution because it will affect multiple amino acids from the point of mutation causing the amino acid sequence of the polypeptide to be entirely different hence the polypeptide is unlikely to function correct because the sequence of bases in dna is read in triplets
What are mutagenic agents? Name four of them.
- UV
- X rays
- Cigarette smoke from carcinogens
- HPV
How do mutagenic agents increase the rate of spontaneous mutations?
By interfering with the DNA’s copying and repairing mechanisms
What are the two forms of chromosome mutations?
- changes in whole sets of chromosomes
- changes in the number of individual chromosomes
What are chromosome mutations?
Changes in the structure or number of whole chromosome
What does polyploid mean?
When organisms have three of more sets of chromosomes rather than the usual two causing a condition polyploidy mostly found in plants
When do mutations in the number of individual chromosomes occur and what does this result in?
In chromosome non disjunction because it results in a gamete having either one more or one fewer chromosomes and if fertilised with a gamete that has the normal complement of chromosomes the resultant offspring have more or fewer chromosomes than normal.
What is chromosome non-disjunction?
When individual nom homologous pairs of chromosomes fail to separate during meiosis
What does meiosis produce?
Four daughter cells which are haploid hence are gametes and have genetic variation
What are the stages of meosis?
Interphase- homologous pair of chromosomes are replicated
Meiosis I - homologous pair of replicated chromosomes separate and the chromosome number is halved
Meiosis II - each of the sister chromatids separate to produce 4 haploid daughter cells
What are the two ways that meiosis brings about genetic variation?
- independent segregation of homologous chromosomes
- crossing over which allows for new combinations of maternal and paternal alleles
What are homologous chromosomes?
A pair of chromosomes where one is maternal and one is paternal that have the same gene loci (the same gene position)
What is crossing over and what stage of meiosis does crossing over occur?
It occurs were the formation of chiasmata between chromatids in homologous pairs generate further genetic variation (check bio album)
What are chiasmata?
The crossing over points between the sister and non sister chromatids of the maternal and paternal homologs to form bivalents when the homologous pairs are crossed over. (Check biology album)
What is recombination?
Where the broken off portions of chromatid recombine with another chromatid in crossing over
What are the steps in crossing over
- The chromatids of each pair become twisted around each other
- This causes tensions and so portions of chromatid break off
- The broken portions then rejoin with the chromatids of its homologous partner ( usually the equivalent portions of homologous chromosomes are exchanged)
- This causes new genetic combinations of maternal and paternal alleles to be produced
What is independent segregation and what stage of meiosis does it occur at?
Where each homologous pair of chromosomes independently and randomly line up on the metaphase plate and so the combination of maternal and paternal chromosomes that go into the daughter cell of meiosis I is random allowing for a large number of possible combinations of chromosomes in the daughter cells. Basically it’s the variation in gametes from the different combinations of the maternal and paternal chromosomes.
Occurs during anaphase and metaphase I.
How can you calculate the number of possible combinations of chromosomes for each daughter cell?
By doing 2^n where n is the number of pairs of homologous chronometer
How can you calculate the possible combinations due to independent segregation and random fertilisation ( gametes)
By doing (2^n)^2 where n is the number of pairs of homologous chromosomes
How is polyploidy and advantage in plants?
As it can cause bigger flowers and so bigger fruit and therefor more profit
What can chromosome mutations lead to in humans and give 2 examples
It can lead to aneuploidy where there is either an extra chromosome of there is one chromosome missing e.g:
- trisomy 21 (Down’s syndrome)
- fragile X (turner’s syndrome)
