Genetics exam 3
other example of trisomies
With crop plants (corn, rice, wheat) trisomies have been identified chromosomes carrying different loci that have some phenotypic affect affect. (trisomy)
reason for difference on incidence
most of 45 X embryos are spontaneously aborted or experience early death (during development they dont make it)
Polyploids in meiosis
nondisjunction happens and yields 2N gamete and it meets another 2n gamete (tetraploid zygote)
Centric fission
occurs when the metacentric chromosome breaks to form two telocentric chromosomes
Homeologous
partially homologous (come from allopolyploids)
Incidence of Klinefelter
seen only 1/2000 live births
Are trisomies bad?
some human trisomies are very bad, others are not. but still affect life negatively
48, XXXY 48, XXXY 49, XXXXY 49, XXXYY
these are much more rare since we need 2 individual non-disjunctions to yield such zygotes (for both egg and sperm) these indiv have phenotypes like klinefelter, but with more severe traits
How can we made mitotic failure happen for allopolyploids?
use colchicine on sterile hybrid so that they go on further and make gametes.
Triploid
when a 2n gamete meets a 1n gamete (normal)
Incidence of Turner
Turner syndrome- seen only in 1/1000 live births
Centric fusion
Two nonhomolgous acrocentric chromosomes join to form a metacentric chromosome
Figure 8.1- Klinefelter
- 47 (chromosome number) ,XXY (should have 1 X) - Klinefelter = Genetilia + internal ducts are male - but testes are underdeveloped + yield no male sperm - have masculine development but with some feminine development as well -specifically: slight breast development common, female pubic hair pattern, tall, intersexuality, poor beard growth - most individuals are trisomic, 44 autosomes (sets 1-22 are normal) but have 3 sex chromosomes + XXY therefore 47
Distinguish between Trisomy, Monosomy, tetrasomic and Nulisomic
- Assume 2N diploid condition, after fertilization with a normal (n) gamete -talking about individual chromosomes - Trisomy 2N+1 (Down syndrome) -Monosomy 2N-1 - Tetrasomic 2N+2 - Nulisomic= No copies of particular chromosome exist (NOT GOOD)
Polyploid Mechanisms
- Autopolyploidy: individual gets all its chromosome sets from same species -Allopolyploidy- Individual gets different set of chromosomes from different species.
Example Allopolyploids
- Bread wheat (Triticum Aestrium) -Allohexaploid= 42 chromosomes -bc 6 chromosomes, it must be derived from 3 different ancestral diploid - each of the 3 species contributed 2 sets of chromosomes (diploid) AABBDD (Figure 5.3) - pairing occurs only between homologous sets - meiosis is normal -> get balanced gametes, in this case its n=21 bc we need 42.
Aside from down syndrome what 2 other trisomies survive birth?
- Patau: 47, 13+ (extra chromosome 13) - Edwards- 47, 18+ (extra 18 chromosome)
Allopolyploids
- doing it with something else -most naturally occuring polyploids are of this kind - can result in a new species
Nondisjunction (most common cause of Down) Fig 8.6
- failure to normally allocate chromosomes to cells during meiosis - happens either in meiosis 1 or meiosis 2 -result- gametes which have 2 members of a specific chromosome or that lack it all together
Figure 8.12- another mechanism of how we may get allopolyploid (from 2 different species)
- haploid pollen grain with genome A may pollinate flowers of a species with genome B - Forms sterile Hybrid (AB) -why is this sterile? bc A is made of 3 components and B is made of 2. Therefore they try to do meiosis, nobody has doubles so they can't pair. - In other words, it is Sterile since chromosomes from genome A are different enough from those of B that they don't pair + operate normally in meiosis
Familial Down syndrome
- happens when one parent has 14/21 D/G translocation -individual has big chunck of G chromosome 21 translocated to end of D group chromosome 14. -individual is different to other humans bc he/she has 45 chromosomes, but have nearly complete locus complement. ( not lacking 14 or 21 stuff) -after indivs undergo meiosis, 1/4 gametes have 2 copies of chromosome 21. -1 of them is normal - 2nd one that has been translocated to chromosome 14
Aneuploid Conditions + Age
- incidence of downs and other Aneuploids rises with age of moms. ex: for a mom who is 45 years old- 50x more likely to have a down syndrome child as a mom who is 20 Math: 1/2,300 = 0.0004 1/46 = 0.002 0.002/0.004 = 50 Cause: is due to way oogenesis works in human females for human females, oocytes are formed before birth. Then are held in a resting state (prophase of meiosis 1 ) until just before ovulation - thus, for a 40 yr old mom, those oocytes have been sitting for 4 decades. they are likely to be influenced by environmental factors.
After fertilization by a normal gamete, non-disjunction zygotes are:
- monosomic: sex cell with no chromosome is fertilized by haploid, so we get 1 chromosome in cell (2N-1) (get 1) -Disomic: sex cell with 1 chromosome (haploid) is fertilized by another haploid (2N) Normal (get 2) - Trisomic: sex cell with 2 chromosomes (diploid) is fertilized by another haploid (normal) (2N+1) (get 3)
Mechanism of G. Karpechenko 's experiment
- probably mitotic failure in some tissue, now it becomes germinal & does meiosis. -plants are both 2n=18 and form gametes n=9. bc its odd, when they form plant, its sterile - plant self pollinates (2n combines with 2n bc it has mitotic failure, and it produces 4n) - it forms gametes and get 1 gamete that is 2n=18 and another gamete that is 2n=18. - put it together and we get 4n=36
Figure 9.6 (Autotetraploid)
- since 4 is an even number, you can get regular meiosis (but not always) - key factor= how the chromosome of 1 type, pair and segregate - there are 3 ways to do so- the ones that work are the 2 bivalent + quadrivalent 2 <-> - in the univalent and trivalent, one chromosome has 3 and other has 1
Aneuploidy
- when you have gametes that have an extra chromosome (s) of a particular type -either have more or less than what we should have -Trisomy, Monosomy, tetrasomic and Nulisomic
Colchicine in plants
- with plants, if colchicine is often applied to merisematic tissue (growing tip of stems and branches) then look with microscope to find altered cells (4n) - once seen, they are removed, you put it on nutrient agar medium -tissue will develop into a whole plant. Plant is 4N, fertile and yield normal seeds.
Important Agricultural Varieties tetraploids (polyploid)
-Alfalfa -Coffee -penuts -McIntosh Apples - Larger and/or grow more vigourously than diploid/triploid relatives
Alternate Segregation (type of reciprocal translocation)
-Diagonally arranged (Across) -pink and pink go together, orange and orange come together. -when they pull apart, they produce balanced chromosomes ( same # of loci, nothing is lost each gamete has a full set of chromosomes) - When alternate centromeres go to same pole, chromosomes form figure 8, in early anaphase 1
example triploids
-bananas & watermelons - make unbalanced gametes and are therefore sterile - these commercial forms are propagated by cutting. This means you take existing plant, take piece off and let grow. Grow new plants out of small pieces of plants
Polyploidy
-common in plants - rare in animals (some beetles, Salamanders, earth worms, fishes)
Animal trisomies
Trisomies to other aneuploid conditions are less common - examination of spontaneous abortions shows that nearly all monosomies (don't have have any) and many trisomies lead to fetal death.
David H. Carr
-Did karyotype analysis of spontaneously aborted fetuses - his review shows about 15-20% of all conceptions are terminated by spontaneous abortions - 30% of those spontaneous abortions show some form of chromosomal abnormality. 70% are not genetically related - 90% of all chromosomal abnormalities are terminated prior to birth via spontaneous abortions - of all abortuses, a big portion are Aneuploids (most common 46, X (Turner syndrome) if fetus lives to birth) some are aborted - a big portion of abortuses were trisomics for one of each human chromosome (every single chromosome) 1 trisomy for chromosomes 1-23 pairs - Also found that Monosomies ( missing something) were seldom found. this is odd since nondisjunction should make n-1 gametes as often as n+1 gametes. (should be at equal frequency) - Having monosomies r worse - thus gametes that lack a single chromosome (n-1) are functionally debilitated. or that embryo dies very soon in development, that aborted fetuses seldom occur (simply terminated early in dev) - some polyploid cases (terminated embryos with a whole complete set or more of 23 chromosomes) were also found. Overall, normal embryonic development requires/needs precise diploid complement needed to maintain normal equilibrium in expression of genetic information - early termination of such cases prevents a bad impact on human gene pool
Down syndrome
-Discovered in 1866 by Langdon Down -only autosomy trisomy (autosomy = not sex chromosom, trisomy- 3 doses of something) - for which individuals live longer than a year - trisomy for chromosome 21 (47, 21 +), have an extra 21 chromosome (should have 2, but have 3) - incidence = 3 infants in 2,000 have down - produced in 2 ways- Nondisjunction,
Monosomics
-Do not develop as zygotes do not develop well
Reciprocal Translocation
-Figure 4.28 -Exchange of material between non-homologous chromosomes. -3 types: alternate segregation, adjacent-1, adjacent-2 segregation
Kline Felter + Turner Syndromes
-Have developmental phenotypes characterized by Aberrant sexual development
A hexaploid has 60 chromosomes in gamete
-Hexaploid means 6X. -Therefore, 6X=60 X=10 - 2N=60 - n=30 -x=10
Sex determination: Evidence / Clues
-Kleinfelter + Turner- These show that Y determines maleness and femaleness even if only 1 is present - when Y is absent- sex is female even if only 1 X is present - when only 1 X is present, no masculine traits occurred - the fact that Klinefelter has a Y and is basically male shows that Y is key for maleness
How to investigate trisomies ? Figure 4.36
-Look at crosses that involve trisomic plants since they yield odd segregation ratios - Homozygous dominant plant AA crossed with recessive diploid aa -F1 = 1/2 AAa & 1/2 Aa - back cross with aa - AAa x aa Trisomic individual will make gametes in a ratio that is unique gametes from AAa -> 1: AA 2:Aa 2: A 1: a ( 1 : 2 : 2 : 1)
How do you resurrect this from the dead? how do you go from middle to end? went from a single a1 to double a2. EVERYTHING DOUBLED (FIGURE 8.12)
-Not everything is lost (sometimes) -happens randomly: all is not lost. sometimes, if mitotic failure happens (trying to take 2n trying to take gen material to produce 2 2N sitting side by side. in mitotitc failure, you take all doubled chromosomes and put in one cell) somewhere on branch/plant, Some cells which are AABB may result. Not everywhere on the plant. only some cells. -if genetically different, phenotype will be different. the more you wait, the more different it will be - then you find them or notice them, culture on media, you now have a new plant. - if it is self fertile, you have made/facilitated an allopolyploid
What would you get normally? (figure 4.36)
-Note when we did AAA x aa only 1/6 of progeny will be aa. (trisomic) - of locus in question had been on a chromosome not in trisomic state, F1 would have been Aa, 1/2 of offspring should be aa.
Table 4.5
-Shows gametes & zygotes for both normal meiosis and non-disjunction cases - There are 4 common & viable abnormal chromosomes: XO (O= lack sex chromosome in gamete or Zygote), XXX, XXY, XYY
Figure 2.29 (cell of clarkia, a plant)
-Some plants & few animals have a series of reciprocal translocations such that heterozygotes have mostly all chromosomes associated in a big ring or rings in meiosis -But at Anaphase, these chromosomes come out of ring like formation and experience orderly alternate segregation. They yield zygotes that have balanced chromosome complements (normal gametes)
How do humans deal with genetic problems?
-Spontaneously abort fetuses -more than 1/2 of al of them occur within first 3 months of development - cases of aneuploidy, polyploidy, ect.
Triploids
-When they split to make gametes, there is uneven allocation of chromosome (can't have 1.5 chromosomes) -they can live but are normally sterile due to low probability of making balanced gametes. - Also true for polyploids with an odd number of chromosome sets (pentaploids, heptaploids ect...)
Adjacent Segregation
-adjacent centromeres segregate together -> adjacent segregation (Same side: either top/bottom or right/left come together) -Products are unbalanced: results in duplications and deletions in gametes - chromosomes form a ring -NOT GOOD
Rate of segregation for alternate and adjacent translocation
-alternate + adjacent segregation takes place at an equal rate -in other words, some sex cells do adjacent segregation, while others do alternate segregation. Both happen at the same time and at the same rate.
what is colchicine
-an alkyloid compound derived from autum crocus plant -has the effect of interfeering with spindle formation (without being able to move, they aren't allocated properly) -thus replicated chromosomes can't enter anaphase or migrate to poles. -Cells re-enter interpahse bc of no wiring to move where they should go. After a while, they don't like to be in interphase for a long. Eventually they enter anaphase again. When paired sister chromatids separate + uncoil, nucleus now has twice the diploid number (4n) Colchicine is present still so they cant move. -these new cells multiply and form small patch of tissue that can be recognized microscopically Figure 8.11
Incidence of Polyploids
-are found naturally but in low frequency (result of abnormal mitosis or meiosis)
Semisterility
-condition that occurs when sex cells segregate, where 1/2 gametes of a translocation heterozygote will be non-functional. - operates differently for animals vs plants. Plants: unbalanced (duplication/deletion) gametes generally abort while still gametes. Never have offspring with defects animals: they are viable gametes, but lethal to zygote
Mechanism for a diploid pollen grain (fig 5.2)
-diploid pollen grain fertilizes a diploid egg (result of a non-disjunction bc pollen should be haploid) of same species. -result= zygote is tetraploid (bc has 2 pairs)= Autotertraploid/AAAA A= indicates a complete chromosome set of genotype A -ALSO, a diploid pollen grain of species 1 fertilizes a diploid egg of species 2. Result is Alotetraploid AABB (AA from one species BB from other species)
balanced
-each gamete has full set of chromosomes. -either get 2 untranslocated or 2 balanced translocated (in figure 4.28: ones on the left are translocated, evident by diff colors)
Qualities of autopolyploid plants
-generally larger than diploid relatives (larger fruits and flowers) - How do you get larger plants? increase in size due to larger cell size rather than increasing cell number Frames A, B, C (figure 9.5)
Allotetraploid mechanism for pollen grain (fig 5.2)
-have a diplod pollen grain of species 1. -fertilizes a diploid egg from species 2 -Result- Allotetraploid (AABB) A indivades the chromosome set or genome of species B -usually closely related species
Plants and Polyploidy
-nearly 1/2 of all flowering plants are polyploid -Potatoes: tetraploid 4X=48 - bread wheat: hexaploid 6X=42 - Strawberries: octaploid 8X=56
What is the primary cause of Down
-over 95% of cases of down syndrome are due to non-disjunction (on karyotype chromosome 21 has 3) - Chances of parents who have child with down syndrome, due to nondisjunction, chances of getting second child with down are lower
Important Agricultural Varieties triploids(polyploid)
-potato species- genus solanum - winesap apple -commercial bananans -watermelons (seedless) -Tiger lily (cultivated) Lilium Tigrium ** ALL PROPAGATED ASEXUALLY
describe Patau and Edwards similarities
-syndromes -both produce big malformation -early death
What is the other (less common) cause of Down?
-translocation (figure 8.20) -higher frequency of occurence over several generations
why will triploids be imbalanced (figure 9.4)
-triploid trying to allocate 3 sets of chromosome (50/50) -Autotriploid: pairing during meiosis usually occurs betwee 2 chromosomes at a time - you can take 1 & 2 and send 3 the other way (1+2/3) or you can take 1 and 3 and send 2 the other way (1+3/2) or you can take 2 & 3 and send 1 the other way (2+3/1) - Always results in unbalanced gametes
How do Autotriploids arise?
1. Rely on non-disjunction= diploid gamete (2N) meets gamete haploid (1N) (triploid zygote did it by itself, with one species) 2. Sperm (1N) two of them fertilize a normal haploid egg at same time (1N) 3. By crossing a diploid with a tetraploid. When you think of gametes made: we get 1N (from diploid) 2N (from tetrapolid) when 1N and 2N meet, you get a triploid
Why is polyploidy rare in animals?
1. Sex determination systems is often sensitive to polyploidy, more so in animals than in plants 2. Plants (many of them) can practice self fertilization, so 1 new polyploid plant if it has an even chromosome set (hex a, ext.) can still reproduce 3. plants can regularly hyberdize easily with other related species. Allows for different sets of chromosomes from different species placed into a single polyploid individual
Results
1/2 of gametes of gametes of a translocation heterozygote will be non-functional (semisterility)
Turner
45, X - female external genetalia + internal ducts but with rudimentary ovaries -short stature - short webbed neck -broad shield like chest -monosomic- 45 total chromosomes with only 1 X
Figure 4.5 other ways of getting Turner
45, X = other karyotypes can also yield these traits ex: when some individuals have 2 separate cell lines. each diff cell line has own karyotypes. These individuals are mosaics (bc their body is made of cells with diff genetic conditions) this condition arrises from mitotic errors in early development most common: some cells in body are 45 X while others are 46 XY (normal) other common: some are 45 X, while others are 46 XX
Metafemale syndrome
47 XXX - normal set of autosomes + XXX - experience female development - incidence 1/700 - 1/12,000 (incidence values vary on where you are) live births -in terms of phenotypic expression- highly variable - totally normal female development. on other extreme, we have underdeveloped secondary female characteristics; sterility; mental retardation Other genotypes: 48, XXXX 49, XXXXX phenotype is like 47 XXX but more severe / pronounced thus having extra X disrupt normal development, balance is disrupted.
another name for autotetrapolid
AAAA
figure 9.19
Aaa -> 1: A 2: Aa 2:a 1:aa - of you are trisomic, you must send 2 to one side and 1 to another. Always will get 1:2:2:1 ratio (only thing that will vary are which chromosomes are where) - if you get this, there is probably a trisomy for one of the chromosomes you are working with
Autotetraploid
Chromosome sets are homologous (as in a diploid) bc they come from same species
How are Human chromosomes divided?
Divided into 7 different groups- based on size and centromere position -A (1-3) BIGGEST -B (4-5) -C (6-12) -D (13-15) -E (16-18) -F (19-20) -G (21-22) 23 is on its own bc its sex chromosome
Autosomal Aneuploids
Does not refer to sex cells 22 sets
Translocation+ Human disease
Down syndrome-
what are the 2 ways that Changes in chromosome number can occur?
Euploid Types: number of chromosome sets differ euploidy increase in number of complete sets of chromosome Aneuploidy: the number of a specific is not diploid. variation in the number of a particular chromosome within a set generally leads to an abnormal condition because it leads to an imbalance in amount of gene products (too much or too little)
G. Karpechenko - Russian 1928
Example of Allopolyploid - in genetics garden crossed (Brassica) cabbage with a radish (raphanus) - both have chromosome #18 - Why did he do this? goal= wanted a hybrid that had leaves of a cabbage+ roots of a radish - eventually, recovered a few seeds from the hybrid and he planted them - he finds they were 4N=36 an fertile ( plants were 2N=18, therefore, their gametes must be n=18. but instead they did 2n+2n= 36 (4n=36) ). - got traits: radish leaves with cabbage roots (opposite of what he wanted) Known as Raphanobrassica: Amphidiploid -
Figure 8.10
Focuses on non-disjunction for translocation as long as someone is translocation carrrier, there is 25% they will make down child. the only way that translocation stops from reappearing is if parent does not have children
What has the greatest impact on survival?
Generally, changes in chromosome number (aneuploidy) have a bigger impact on survival or change in structure
polyploids in mitosis
If all chromosomes in a diploid (2N) cell are doing mitosis, they go to some pole ( remember in mitosis, supposed to double cell complement so that each resulting cell is 2N). But instead, all chromosomes go to one side. So one cell has no chromosomes. Resulting cell is autotetraploid
XYY
Most controversial 47, XYY 1965- Patricia Jacobs - she examined penal colony in a maximum security prison in scotland - she found 9/315 males had the condition (karyotype) - those 9 individuals were very tall + had been involved in serious criminal acts - all 9 had personality disorders - follow up studies showed (around other countries) same pattern - these studies compared frequency of 47 XYY condition with conversely criminal + noncriminal populations - overall, incidence of above normal height and below normal intelligence in penal populations was high and frequency of 47 XYY was also high. -Jacobs- link between genetics + behavior suggested: behaviors= antisocial + criminal behavior, genetics= 47, XYY. -But others said there are also individuals with 47 XYY who are not institutionalized (penal/mental) and lived normal lives. In all cases, these indvs are very tall TAKE HOME MESSAGE: no direct correlation between 47 XYY & bad behaviors
Polyploidy (Euploidy variation)
Organisms with 3 more more sets of chromosomes, If haploid chromosome= X, for organism with 3 chromosome sets= 3X (triploids) 4X (tetraploid) 6X (hexaploid) * for multiple chromosome organisms, X stands for chromosome number -For X organisms that are regularly polyploid (many plants) X= number of chromosomes in a set -n^2 = number of chromosomes in gamete
Minor Mechanism that can change chromosome number?
RECIPROCAL TRANSLOCATION: If this involves 2 acrocentric chromosomes such that the large segments reattach & small chromosomes may be lost during cell division CHROMOSOMAL (CENTRIC FUSION): 2 non-homologous chromosomes, acrocentric join at centromere form metacentric chromosome. -Conversely, chromosome may split at centromere perpendicular to its length. results in 2 smaller chromosomes -> unite -> chromosomal centric fission -generally fusion are more common than fission
Are trisomics viable? Figure 8.8
Trisomics are usually viable & common in plants but less viable/ common in animals
What affects a big portion of abnormal new borns
Trisomies and Aneuploidies comprise a big portion of genetically abnormal newborns
Allopolyploid
diff chromosome sets vary somewhat. Have some similarities bc they are closely related but also differences Called Homeologous- partially homologous
Amphidiploid
double diploid (went from 2n to 4n)
Datura Stramonium
example of trisomic plant Figure 8.8 Alfred Blakesee worked in 1920 with Jimson Weed (Diturium Stamonium). He finds a series of Datura Mutants (all one species that act differently): they have strange properties - each were trisomics for different individual chromosomes 2N=24, n=12 (chromosomes) - found trisomies for each of 12 chromosomes phenotypes for seed capsules are all a bit different - he says that each 12 chromosomes has small impact on seed capsule. ( top of the plant) -if there are extra for any of the 12, there is a slight difference on the entire plant?
How else can polyploid cells be made?
experimentally from diploid cells -apply shocks -apply heat or cold shocks -apply colchicine material to somatic cells during mitosis
Diploid Bananas
have hard seeds (wild bananas), but commercial triploids "seedless" have edible seeds
