Topic 8.1 Genetic information Flashcards
Suggest factors that increase genetic varaition
- mutations
- crossing over
- independent/random assortment
- random fertilisation
Define mutation
a permanent change in the DNA of an organism
Why might a mutation not lead to a change in the amino acid sequence?
DNA code is degenerate, which means it may end up coding for the same amino acid unless a frame shift occurs
What are insertion and deletion mutations?
where 1 or more nucleotides/bases are either inserted or deleted from the DNA sequence. leads to frame shift so more likely to be harmful
What is a substitution mutation?
when a nucleotide in the base sequence is replaced by another- less likely to have an effect on the amino acid sequence
How can meiosis processes create new combinations if alleles?
- chromosomes line up randomly, maternal and paternal chromosomes are distributed randomly into gametes
- crossing over of chromatids before first division
How does random fertilisation bring about genetic variation?
the combination of the 2 gametes that fuse is completely random and each gamete contains different DNA
Define genotype
the genetic makeup of an organism with respect to a particular feature
Define phenotype
the physical traits (including biochemical characteristics) expressed as a result of the interactions of the genotype with the environment
Define allele
different forms of a particular gene found at the same locus on a chromosome, a single gene can have many alleles
What is meant by codominant alleles?
both alleles are expressed and the proteins they code for act together without mixing to produce a given phenotype
What is meant by multiple alleles?
there are more than 2 possible variants at a particular locus
Why are ratios predicted from genetic crosses never precise?
- chance: combination if alleles is completely random
- some offspring die before they can be sampled e.g. some seeds don’t germinate and some embryos miscarry
- inefficient sampling techniques e.g. letting insects escape
Give explanations as to why there are occasions where ratios from dihybrid crosses are not what you expect?
- small sample size
- experimental error (organisms escape or die easily)
- process is random so sometimes the unexpected happens
- unexpected ratios can be the genes being examined are both on the same chromosome (linked)
Define polygenic inheritance
-more than one gene for a single characteristic
-on more than one locus
-genes interact with each other
polygenic phenotypic traits are determined by several interacting genes
