Lecture 14 - Phenotypic variation and inheritance Flashcards
what is inheritance?
inheritance or heredity:
> some traits (physical or biochemical characteristics) are heritable - they are passed on from one generation to the next.
>related individuals look more alike than unrelated ones.
define heredity
the phenomenon by which offspring resemble their parents
define variation
why offspring are not identical
what are the principles of heredity?
> inherited characteristics are determined by genes
all individuals of a species have the same base set of genes
variation is due to gene mutation
variants of the same gene - alleles - account for variant traits.
what s a genotype?
> genotype is the allelic constitution of an individual (can refer to one, a few, or many loci)
what is a phenoype?
the trait value of an individual (under the combined influence of genotype an environment)
> e.g., brown eyes/blue eyes
how do you get different alleles of a gene?
changes in genotype arise from mutation of genomic DNA
> mutations are changes in the DNA sequence
what are the different types of mutations?
> point mutations - single nt changes
insertions or deletions
translocations, deletions or duplications - large scale chromosomal changes.
- silent, mis-sense and non-sense
mutations can be in the coding region or the non-coding region of DNA.
mutations can occur in somatic cells or germ cells.
what type of mutation can cause leukaemia?
a reciprocal translocation
> the ABL oncogene from chromosome 9 is replaced with a segment from chromosome 22.
>chromosome 22 now has the ABL gene and is now called BCR-ABL.
>this is called the Philadelphia chromosome.
>causes an over proliferation of cells, thus leukaemia
what are the causes of mutations?
> spontaneous mutations result from internal cellular processes
- mis-incorporation of nucleotides during DNA replication
- these are mainly due to very rare errors during DNA replication (and the molecular DNA repair machinery in the cell takes care of most of them)
- in humans mutation rate is ~ 1 in every 2x10^8 base, or about 100-200 mutations accumulating from one generation to the next.
- errors during meiosis causing chromosomal abnormalities (wrong pairing up of homologous chromosomes)
induced mutations result from external mutagens
- e.g., UV light, mutagens such as chemicals (represses repair)
what are the outcomes of mutations?
> loss of function mutations
- interfere with the ability of a gene to code for a fully functioning protein
- or can be regulatory mutations affecting gene’s promoter
- mis-sense - changes amino acids
- non-sense - produces a stop codon
silent mutations
- have no affect on protein function
gain of function
- these are usually dominant and result in a protein with altered functionality.
what is an example of a genetic disease caused by a mutation in a single amino acid?
sickle cell disease:
> in the gene sequence for hemoglobin, an A is swapped for a T, causing the sequence to change from thr pro glu glu to thr pro VAL glu
> this single nt change leads to sickle cell anemia
what is the difference between smatic and germ line mutations?
> somatic mutations occur in the soma, the cells of the boy not involved in producing sex cells
germ line mutations happen in the germ cells, and are therefore inherited.
most mutations occur in the soma
what is an example of a mutation in the somatic cells?
cancer
> cancer is the outcome of mis-regulation of the cell cycle caused by genetic mutations
what is an example of a cancer that occurs in the germ line and is therefore heritable?
some forms of breast cancer and ovarian cancer. E.g., BRC1 and BRC 2 genes.
