Definitions Flashcards
Def: Point mutations
- Change in a nucleotide(s)
- New genetic variation
Def: Chromosomal mutations
- Important source of new genetic variation
- Can cause developmental defects and disease in humans
- Are structural changes in a chromosome OR duplications/deletions of whole chromosomes
Name the four types of chromosomal mutations?
1) deletion
2) duplication
3) inversion
4) translocation (chromosomes exchange segments)
What are the causes of chromosomal mutations?
- chromosome breaks during DNA synthesis and crossing over
- radiation, chemicals
- transposable elements of DNA
- recombination errors during cross-over
- broken ends are sticky and may rejoin in a new configuration
What may be a significant factor in maintaining reproductive isolation between species?
Non-lethal chromosomes
What are the effects of non-lethal mutations?
- alter meiotic pairing
- alter effects of recombination (crossing over) and the genotypes of gametes
- can be studied genetically
Pericentric vs Paracentric inversions
Pericentric: cross-over products inviable, centromere involved
Paracentric: cross-over products inviable, centromere not involved
How do chromosomal mutations play a role in Downs syndrome, leukemia, lymphoma, and cancer cells?
Downs syndrome: a reciprocal translocation causes one form of this
Leukemia and Lymphoma: translocation interrupts a gene involved in cell cycle regulation
Cancer cells: have “genomic instability” due to mutations in DNA repair genes
Are there chromosomal mutations on the human Y chromosome?
- none fully proven to be truly Y-linked
- Chinese study of hearing impairment?
How do deletions affect a homozygote where the centromere is retained?
-the gametes are inviable due to missing genes
If a chromosome loses it centromere due to deletion, what happens?
- the whole chromosome is lost
- usually lethal
How do deletions affect a heterozygote where the centromere is retained?
- if wild type alleles are on the complete homologue, phenotype is normal/wild type
- if recessive mutation on the complete homologue, recessive phenotype expressed = pseudodominance (unexpected expression of recessive allele due to absence of dominant allele)
Def: Pseudodominance
unexpected expression of recessive allele due to absence of dominant allele
Name the three types of duplications.
1) tandem repeat
2) reverse tandem repeat
3) terminal tandem repeat
What are tandem repeats used for today?
-DNA fingerprinting
What is an example of duplication where in evolutionary time, the extra gene copies took on new functions?
- globin genes
- code for protein subunits of hemoglobin
- multiple globin genes in humans
- genes with greater 02 affinity expressed in the fetus
What are some genetic consequences of inversions?
- homozygous mutant still has all the genes and is normal unless there is an inversion break or the position affects gene expression
- heterozygous mutant often have decreased fertility due to cross-over events within the inversion
Are the gametes viable or inviable after a:
A) paracentric inversion
B) pericentric inversion
A) 50% viable and 50% inviable, inversion heterozygotes may have reduced fertility
B) 50% viable and 50% inviable
Def: Reciprocal translocation
2 non-homologous chromosomes exchange segments
During translocations, what are the two possibilities of what happens at anaphase I?
1) alternate segregation
- alternate centromeres segregate to same pole (50%)
- (N1+N2) vs (T1+T2)
- all gametes are viable (receive all genes)
2) adjacent segregation
- 50% of the time
- (N1+T2) vs (T1+N2)
- both not viable since some of the genes are missing, deletions and duplications
- fertility is reduced by about 50% in translocation heterozygotes
Def: Aneuploidy
- changes in 1 or a few chromosomes
- due to non-disjunction during meiosis
- often decreases fertility because meiosis is abnormal
- can change phenotypic ratios in offspring
Def: Euploid
- complete set(s) of chromosomes
- euploid number varies among species
In wild species, what is the frequency of polyploidy?
-unreduced gametes occur at about the same rate as point mutations
Rank the frequency of polyploidy in the following species: invertebrates, vertabrates and plants
highest to lowest frequency:
1) plants (40-70%) = high
2) invertebrates (42%) =variable
3) vertebrates (0%) =low