Chromosome Variation (Chpt 8) Flashcards
What are most animal species and many plants?
-diploids (2N)
What is Monoploidy?
-only one set of chromosomes (N)
-ants bees and wasps have monoploid males
What is polyploidy?
-more than two sets of chromosome
-includes Triploid (3N) have the same set of genes but can have different alleles
-tetraploid (4N) 16 total
-plant kingdom: 30-35% of flowering plants are polyploids
-animal kingdom: polyploidy is rare
What are autopolyploid?
-the chromosome sets are all identical and copy what you have
-All chromosomes are derived from the same species
-evolves from a hybrid and plants cross with different species successfully to become hybrid
-Autopolyploids usually have:
-more vegetative growth (larger cells thicker leaves bigger flowers, large plants and bigger fruits)
-less seed production
Polyploids are sterile and seeds result in sexual fertilization
What is autopolyploidy through mitosis?
-diploid (2N) early embryonic cell goes through replication where the sister chromatids are separated
-no cell division occurs (cytokinesis)
-autotetraploid (4n) cell is produced and prepares to split by doubling but does not split
What is autopolyploidy through meiosis?
-starts as diploid (2N) to replication where non-disjunction occurs
-in Meiosis II sister chromatids are separated produce two cells with 2 pairs of sister chromatids to produce the 2n gamete
-merge to get 1n (fertilization)
-this then fuses with 1n gamete to produce autotriploid
-zygotes are early embryonic cell mitosis works well
What are the problems with polyploidy?
-many polyploids are sterile due to problems with pairing and separation of homologous chromosomes in meiosis
-the number of chromosomes in a gamete from a banana cultivar can vary
-gametes that have extra chromosomes or lack certain chromosomes are not viable
What happens in Meiosis I of polyploidy?
-in meiosis I metaphase I mitotic spindle separates the bivalent and goes to anaphase I
-11 bivalents and 11 univalents
-2 11 bivalents can form 9 pairs are leaving one out univalents
11 trivalents all want to recognize each other and because so tightly packed together they all get stuck as a group of 3
What happens in Meiosis I and Meiosis II of polyploidy?
-two homologous chromosomes pair whereas the other segregates randomly
-anaphase I pairing of two of three homologous chromosomes
-all three chromosomes pair and segregate randomly
-pairing of all these homologous chromosomes none of the chromosomes pair and all three move to the same cell (no pairing)
-Meiosis II: some of the resulting gametes have extra chromosomes and some have none
How can each chromosome set make a segregation decision?
-human diploid gametes are almost always the same
-want gametes to be perfect alignment to your partner
-11 trivalent not likely
How does allopolyploids work?
-some polyploids are the result of crosses between 2 or more species usually related species
-start with two diploid plants that will always produce AB gametes
Step 1: Gametes from two diploid plants unite to form a hybrid A & B
Step 2: The hybrid is sterile because meiosis is highly irregular AB
-can propagate asexually
Step 3: The chromosomes are doubled creating a tetraploid but don’t divide AA BB
-has partner to pair with can produce consist gametes all the time 4 sets you have even though they are not homologous
Step 4: Meiosis in the Tetraploid is regular A chromosomes pair with A chromosomes and B chromosome pair with B chromosomes
Step 5: The euploid gametes produced by the tetraploid can combine to propagate the organism sexually
How does plant AABB form?
-meiosis I cannot occur because chromosome set from A and B are not compatible (homologous) they cannot align during Meiosis
-this plant is still viable because plants can reproduce asexually
-but plants have the ability to double their chromosomes spontaneously
Plant AB is not Plant AABBB (4N)
-not homozygous: can’t perform mitosis and is sterile
-4N tetraploid all cells are 4N Meiosis I and Meiosis II humans 2N gametes
What is an allohexaploid?
-example is wheat Triticum monococcum
-2N=14 is sterile with 7 pairs of chromosomes in each pair
-reduces to N=7 gamete
-the sterile 2N=14 cannot undergo mitosis because it has no homologous chromosome
-it doubles to 4N=28 to become fertile
-within the 4N= 28 resides the two original 2N=14 plants that were crossed now becomes fertile
-can go from 3N=21 (amphidiploid) and double to 6N=42 (allohexaploid) don’t have groups of 6 have 6 chromosomes
-mitosis can form in this situation because it does not care about pairs but meiosis cannot
What is an example of an allotetraploid?
-upland cotton which is an allotetraploid 4N=52 or amphidiploid 2N=52
How is Triticale developed?
-low protein levels high lysin and does well in poor soils (Rye) 2N=14
-wheat high protein levels low in lysin does poorly in poor soils 4N=28
-thought that crossing these two would create a hybrid with both traits
-cross = 3N=21 sterile to 6=42 allohexaploid triticale functional diploid or amphidiploid
-21 bivalnets will form in Meiosis I