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
What is triticale?
-has the high protein conetent of what and high lysin content of rye hardy even in poor soil conditions
-random genetic chance crossing these two might not always work
-might get both the positive of the traits gene combinations are random
What is polyploidy in animals?
-interspecies crosses can result in a sterile animal
-chromosome doubling which potentially could restore fertility is not well tolerates
-very sensitive to gene copies
What is Anueploidy?
-diploid genome which lacks a chromosome or has an extra chromosome
-2N + 1 trisomies one of the groups of two has a third
-2N-1 monosomies (have all groups of two but one is missing one (one is single)
-meiotic non disjunction can cause aneuploidy
How does nondisjunction occur in Meiosis I?
-no separation of sister chromatids they travel together on the same mitotic branch
-gametes occur one A and one a in meiosis II normal gamete one
-fertilization two zygotes trisomic (2N +1)
-two monosomic (2N-1)
How does nondisjunction occur in Meiosis II?
-2 pairs 4 chromosomes
-one pair goes into 1 and one goes into another
-non disjunction occurs where each chromosome is separated
-fertilization occurs zygotes are trisomic (3 chromosomes) 2N+ 1
-monosomic 2n-1
-two normal diploids 2n
What is Meiotic Nondisjuncation?
-in humans autosomal monosomies are lost early in pregnancy
-only three autosomal trisomies are seen as live births
-trisomy 21 (Down syndrome) humans can live with for many decades
-3 is bad not long shortest contains the least amount of extra genes
-trisomy 13 (Patau syndrome)
-trisomy 18 (Edwards syndrome)
What Aneuploid Conditions involve sex chromosomes?
-everything is tolerated for monosomies
-X0 Turner syndrome
-XXY Klinefelter syndrome
-x variation inactivates all X’s except one
-XXX Triple X syndrome
-XYY Double Y syndrome
-non-disjunction of y chromosomes
What does the frequency of trisomies increase with?
-age older mothers are more likely to give birth to a child with down syndrome
-in the human femal efetus meiosis begins and then arrests (stalls)
-germ cells remain in an arrested prophase I until ovulation
-meiosis I stalled
-homologous pair finds each other in prophase one to exchange genetic DNA
-not stuck with allele combinations we get
-physical interaction with no homologous pair
-prophase recombination
-chromosome can fall off spindle the you are in prophase I
Why is there a correlation between the incidence of trisomies and maternal age?
-theory is if the bivalent dissociates non disjunction of the homologues occurs
-why might the association between sister chromatids (cohesion) breakdown in older woman is unknown
How does Down Syndrome occur?
-96& due to meiotic nondisjunction events
-approximately 80% occur in oogenesis in the mother and 20% occur in spermatogenesis of the father
-random non-disjunctions occur
What are the symptoms and treatments of turner syndrome XO?
-short stature wide chested
-inactive X
-normal IQ
-webbing of the neck is typical
-ovaries fail to develop uterus and oviducts can be small and immature
-treatment is to recieve growth hormone therapy to increase their stature
-receive estrogen at puberty for breast development
What are the symptoms and treatments of Klinefelter syndrome XXY?
-cells inactivate second X
-phenotypic features developed after puberty
-breast development and female body fat distribution can be seen in xxy males
-gives female trait error with testosterone
treatments: testosterone therapy coupled with breast tissue removal will result in a more typical male phenotype
What are the symptoms and of Triple X Females?
-phenotypically normal
-can be taller than average
-some fertility problems
What are the symptoms and of XXY Males?
-phenotypically normal
-usually taller than average
What are deletions and duplications of chromosome segments?
- a deletion or deficiency is a missing chromosome segments
-a duplication is an extra chromosome segments
What is hyperploidy?
hippie is less genetic materials such as deletion of a chromosome segments or the loss of an entire chromosome it is more genetic materials such as a duplication of chromosome segments or gain of entire chromosomes
How is chromosome structure rearranged?
- a chromosome may become rearranged internally or it may become joined to another chromosome
What is paracentric inversion?
- the formation of inversion Loop which excludes the centromere
-pericentric inversion does include the centromere
-the heterozygote has one normal chromosome and one chromosome with an inverted segments
-in prophase 1 of meiosis the chromosomes form an inversion Loop which allows the homologous sequences to align
-does this to minimize non-destructive
What are translocations?
-they occur when a segment from one chromosome is detached and reattached to a different non homologous chromosome
-in a reciprocal translocation pieces of two non-homologous chromosomes are exchanged without any net loss of genetic material
How does structure and pairing of reciprocal translocation occur in chromosomes?
-step one an individual heterozygous for this translocation possesses one normal copy of each chromosome
-step two one translocated copy of each either blue or red gene or are missing a gene
-step 3 because each chromosome has sections that are homologous to two other chromosomes across like configuration forms and prophase one of meiosis they are intact
-step four in anaphase 1 the chromosome separate in one of three different ways alternate segregation or adjacent segregation or adjacent-2 segregation which is rare all genes are homologous pairs
-gamets resulting from adjacent 1 and adjancent 2 are nonviabl ebcasue some gens are present in two copies whereas other are missing
WHat are compound chromsomes?
-are compound chromosomes formed by the fusion of homologous chromosomes sister chromatids or homologous chromosome segments produces a very long chromosome
What are robertsonian translocations?
- formed by the fusion of two non homologous chromosomes at their centimeters evolutionary milestone for humans and champions
-Step 1 the short arm of acrocentric chromosome -Step 2 is exchanged with the long arm of another
-step 3 creates a large metacentric chromosome
-step 4 a fragment that often fails to segregate and is lost the metacentric chromosome centimeter is centered corresponds to different acrocentric chromosomes in the genomes of great apes
