Chapter 8 Flashcards
Diploid
Two Sets of Chromosomes (2n)
Monoploidy
One Set of Chromosomes (n)
Polyploidy:
More then. two sets of chromosomes (more than the normal number)
Triploid
3 sets of chromosomes
Tetraploid
4 sets of chromosomes
Where is polyploidy more common?
In the plant kingdom rather than then animal kingdom as humans are more sensitive to gene dosage.
What are autopolyploids?
Species that have more then two sets of chromosomes, where all chromosomes are identical and derived from the same species.
How are autoployploids made through mitosis?
In mitosis, you have your replication of homologous groups, then the sister chromatids split, but not cytokinesis occurs so there is four chromosomes (autotetraploid)
How are autoploids made during meiosis?
A Non-Disjunction occurs during meiosis I anaphase, and during meiosis II a 2n fertilizes with a 1n (mistake gamete) to produce a triploid (3n)
What is a non-disjunction?
A pair of homologous chromosomes has failed to separate or segregate at anaphase so that both chromosomes of the pair pass to the same daughter cell
What are polyploids?
Polyploids are sterile (can not preform meiosis)
What are polyploid plants typically?
Larger, less seed production
What do diploid watermelon have?
Have seeds
What do triploid watermelon have?
No seeds
Why are polyploids sterile?
They cannot reproduce due to problems with pairing and segregation during meiosis
What is the number for commercial bananas?
3n = 33 (triploid)
What is one way chromosomes of the bananas could separate during meiosis using 3n = 33 and what would be N?
During anaphase, two homologous chromosomes can move to one pole, and one homologous chromosomes moves to the other pole
- This forms 11 bivalents and 11 univalent (N)
What is another way chromosomes of the bananas could separate during meiosis using 3n = 33 and what would be N?
They could all travel to the same pole, which would form 11 trivalent (N)
What ways can you have a triploid cell segregate?
During Anaphase II, you can get two homologous chromosomes forming a 2n gamete and the other homologous chromosomes forming into a 1n gamete
Or,
All three homologous chromosomes forming into a 3n gamete, with one gamete absence during anaphase
How many segragation decisions need to be made in a 3N = 33?
11 segregation decisions
What is Alloploidy?
Species that have more then two sets of chromosomes, but they are derived from different species.
How can allopolyploidy be shown?
If diploid pant AA produced with diploid plant BB, they produce a sterile offspring AB
However you can double the chromosomes (producing a tetraploid), which will cause the A chromosomes to pair with B chromosomes and now they can reproduce sexually
What is the result of Allopolyploidy?
4N, where the sister chromatids can pair up into are in the same gamete
How many sterile plants will you produce if you cross a 2N = 14 and a 2N = 14 different species of plants?
2N = 14 sterile plants (Adding 7N + 7N = 14)
- It will separate into an N = 7 Gamete, where they will merge into 2N = 14 in one gamete
How can these plants become fertile again?
If Meiosis fails and the genome doubles from a 2N
- If it becomes 4N = 28 (4 sets of
What sterile offspring are you producing with 2N = 14 crossed with a 4N = 28
A 3N = 31 sterile offspring
(14/2 = 7) and (28/2 = 14)
14 + 7 = 21
When doubled 6N = 42, it is sterile.
Why are polyploids sterile?
Their multiple sets of chromosomes segregate irregularly during meiosis
How can polyploids produced by chromosomes doubling be fertile?
if their constituent genomes segregate independently
What are Aneuploids?
A diploid genome (2N) that lacks a chromosomes or gains a chromosomes
What are two examples of an aneuploid?
2n + 1 Trisomies (extra)
2n - 1 Monosomies (a single, missing)
What can cause aneuploidy?
Meiotic Non Disjunctions (irregular number of chromosomes resulted from an error in meiosis) can cause aneuploidy
What happens to autosomal monomsomies?
The fetus is lost early in pregnancy
What are the three autosomal trisomies that are seen as live births?
- Trisomy 21 (Down syndrome)
- Trisomy 13 (Patau Syndrome)
-Trisomy 18 (Edwards Syndrome)
What happens to Patau Syndrome and Edwards Syndrome?
Both babies die at a young age
XO
Turner syndrome
XXY
Klinefelter syndrome
XXX
Triple X Syndrome
XYY
Double Y Syndrome (1 in 1000) males have this
A diploid organism has 2N = 36 Chromosomes, how many chromosomes would a trisomic member of this species have?
A trisomic is an extra chromosomes
In this case, it would be 37.
Following the format of 2N + 1
Why is there a correlation between maternal age and trisomy 21?
Meiosis I installs itself when the female menstrual cycle begins, however if you do not get pregnant, it remains in an arrest in in prophase I which can last on average from 16 to 40 years.
The longer you are in prophase I, the more fragile your chromosome spindles are and the more fragile they get over time.
Eventually, they begin to break down do to hormonal changes.
As age increases, it is more likely that a women will have more copies of chromosomes in her eggs.
What are some chemicals that could cause non-disjunctions?
Colchine: used in agriculture to force polyploidy
BPA: found in plastics and waterbottles
What percentage of meiotic nondisjunction occur during oogenesis?
About 80%
What percentage of meiotic disjunctions occur during spermatogenesis?
About 20%
Turnery Syndrome - XO
These females are short, and are wide chested
- Webbing of the neck, normal IQ
- Ovaries fail to develop
What is an example of a Mosaic type of turner syndrome?
They have a mixture of cells with normal and deficient number of the X chromosome
What treatments can Turner syndrome patients have?
- Growth Hormones
- Estrogen at puberty
Klinefelter Syndrome - XXY
These men are slightly more female
Breast Development and develop body fat in areas females would get body fat in
What are the treatments for Klinefelter syndrome?
Taking testosterone
XXX Females
- Phenotypically normal
- May have some fertility issues
XYY Males
- Phenotypically normal
- Some cases of severe acne
- Usually extremely tall
What is a Deletion?
A missing chromosome segment
What is a Duplication?
An extra chromosome segment (two copies instead of one)
What is Turner syndrome?
A Monosomy where one copy of a chromosome is present.
What is hypoploidy?
Less genetic material such as a deletion of a chromosome segment or the loss of an entire chromosome
What is hyperploidy?
More genetic material, such as a duplication of a chromosome segment or a gain of an entire chromosome
What is a paracentric inversion?
A structural chromosomal aberrations caused by 180° rotation of the chromatin segment between these breaks, which result from two breaks on both sides of the centromere
What are the steps of a formation of an inversion loop?
- IMPORTANT *
A heterozygote has one normal chromosome and one chromosome with an inverted segment
In prophase I of meiosis, the chromosome forms an inversion loop, which allows the homologous sequences to align to minimize non-disjunctions
Translocations
Occur when a segment from one chromosome is detached and reattached to a different (non-homologous) chromosome
Reciprocal Translocation
Pieces of two non-homologous chromosomes are exchanged without any loss of genetic material
Compound Chromosomes
Formed by the fusion of homologous chromosomes, sister chromatids or homologous chromosome segments
Robertsonian Translocations
Formed by the fusion of two non-homologous chromosomes at their centromeres
A mistake that makes unfeasible gametes
What can translocation cause?
Down syndrome (50% or less - very minor) when chromosome 21 long arm translocates with chromosome 14 long arm
Cancer - moving a gene to a chromosome where it will be misregulated.
