Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
20 Cards in this Set
- Front
- Back
|
Define euploidy and aneuploidy |
Euploidy: multiples of basic chromosome set (genome). Ex monoploid, diploid, triploid, tetraploid, etc. Aneuploid: single chormosome changes, "somy" - trisomy: extra copy of one or more - monosomy: missing copy of one or more |
|
|
Deviations from haploid/diploid |
Natural: “Accidents” – Partial or complete failure of meiosis or mitosis. – Cell fusions – Interspecific hybridization (closely related species) Artificial: Laboratory manipulations – to mimic “accidents” above-treatments with drugs to inhibit mitosis – culture of germ cells to produce monoploids |
|
|
What is monoploidy? |
Monoploidy: condition of single chromosome set inorganism that is normally diploid (different from haploidorganisms such as fungi and algae) - Monoploid eggs almost always fail to develop, since mostchromosomes of a diploid organism carry recessivedeleterious (harmful) mutations in some genes - Monoploids that do develop to adults are abnormal (almostalways sterile - Monoploids are useful for agriculture |
|
|
What is the process for monoploid selection for recessive traits? |
Take cells from monoploid plants, grow on selectivemedia, any that grow are resistant, allow to grow intoadult plant, make diploid sectors and producehomozygous strain for resistance to the toxin/inhibitor |
|
|
What is polyploidy? |
Cell or nucleus containing more than two homologous sets of chromosomes. - Is common in plants, but rare inanimals Autopolyploids: all sets are the same (from singlespecies) Allopolyploids: different pairs of chromosome setsfrom different (but related) species, so only partiallyidentical - homeologous rather than homologous. |
|
|
Describe triploids |
Triploid seeds generated by crossingtetraploids to diploids: Intercrosses produce sterile triploids – Interbreeding selected against – Speciation of parental strains (i.e. diploids andtetraploids). Larger and more robust than diploids. - Sterile: ”seedless”. |
|
|
What is an amphidiploid? |
A plant originating from hybridization between two species in which the chromosome number is the sum of the chromosome numbers of both parental species. |
|
|
What's the difference between homologous and homeologous? |
Homologous: chromosomes that are similar enough in sequence that they can pair during meiosis. Homeologous: chromosomes from relatedspecies carrying many of the same genesbut without enough similarity in sequenceto pair and behave as homologues duringmeiosis |
|
|
Describe aneuploidy in more detail. |
- Aneuploid is an organism whose chromosome numberdiffers from wildtype by part of a chromosome set - Generally the change is by one or a small number ofchromosomes - Can be more or fewer than normal n+1 or 2n+1 etc. - Most arise through non-disjunction during mitosis ormeiosis Disjunction = normal chromosome segregation Non-disjunction = segregation mistakes |
|
|
What is monosomics? |
Monosomics (2n-1) Generally deleterious – Missing chromosome perturbs normal gene balance – Any recessive harmful mutation on the remaining homolog isnow hemizygous and expressed phenotypically – Can affect autosomes or sex chromosomes – *Monosomies for autosomes lethal in early embryos – Monosomies of X human chromosome causes Turnersyndrome: 45 XO (heart defects, other effects) |
|
|
What is trisomy? |
Trisomy (2n+1) Often lethal but some examples of viabletrisomics in humans: XXY - Klinefelter syndrome XYY - 1/1000 live births [phenotypically normal] XXX ~1/1000 live births [phenotypically normal] Down Syndrome is trisomy 21 |
|
|
When do most non-disjunctions occur? |
- Most non-disjunction takes place during MI - Due to a failure to form or maintain a tetrad In female mammals, all oocytes are arrested at lateprophase I from before birth - So proper chromosome attachment to the spindle mustbe maintained for decades - So as females age, chromosome attachments to thespindle may break down leading to non-disjunction. |
|
|
What are the two types of abnormal phenotypes? |
Haplo-abnormal: abnormal phenotype if only one copypresent Triplo-abnormal: abnormal phenotype if three copiespresent Usually there are just a few genes that are responsible for most of the phenotype |
|
|
Why are monosomies worse than trisomies? |
1) Genebalance: monosomics have a1:2 ratio ofgene dosage between genes of the missingchromosome and the others; buttrisomics have a 3:2 ratio of gene dosagebetween genes of the extra chromosome andthe others (a smaller difference in dosage – maybe less harmful) 2) In autosomal monosomies any harmfulrecessive alleles will be expressed (like beinghaploid for that chromosome) |
|
|
What are the different changes in chromosome structure? |
Inversions – Paracentric – Pericentric Translocations Deletions Duplications (aneuploidies) |
|
|
Describe inversions |
If breakpoints occurbetween the genes,there may be novisible phenotype - Breakpoints withingenes can createfusions - could berecessive lethal orhave other phenotypes - Gene order is altered - Recombination can be suppressed within the inverted region - In meiosis homologous chromosomes will still pair up and the correct regions will synapse but causes looping of chromosmes |
|
|
Describe when a loop forms in meiosis in a paracentricinversion heterozygote. |
- Crossing-over within theinversion loop (e.g. singlecrossover) leads to bridge-breakage-fusion cycle(frequency depends on size ofinverted segment) - The two centromeres becomeattached to one another forminga dicentric bridge, which breaksrandomly during segregation,generating terminal deletions Causing: - Gene imbalance - Reduced fertility:in plants causeinviable gametes;in animals thegametes may beviable but causedeath of zygote |
|
|
Describe when a loop forms in meiosis in a pericentric inversion heterozygote. |
- Crossing-over within theinversion loop (e.g. singlecrossover) does not resultin bridge-breakage-fusioncycle; Chromosomes involved incrossover separatenormally - Still produces gene imbalances: half of the meioticproducts will have duplications and deletions with many ofthe same consequences Causing: - Gene imbalance - Reduced fertility |
|
|
Describe translocations |
Arms (or parts of arms) are exchanged between two non-homologous chromosomes. 2 types of meioticproducts that result from the two mostcommon modes ofchromosomesegregation intranslocationheterozygotes: - Adjacent-1 - Alternate |
|
|
Describe deletions and duplications |
unequal crossing-over 1) very large ones are usually lethal (dominant) because:- they upset gene balance (particularly if they’re autosomal). -they may “uncover” pre-existing recessive lethal alleles. 1) most small deletions are recessive lethal (i.e.,in homozygotesthe absence of a small part of a chromosome in both homologuescauses death). Similar (but not identical) to inversions. Loops are present but small. Crossing-over does not cause additional gene loss. |
