Unit 11

Unit 11: Large Scale Chromosomal Changes Worksheet
Define

- Chromosomal mutations- Mutations in chromosome region which effects multiple genes

- Aneuploidy- Gain or loss of a single chromosome

- Polyploidy (aberrant euploidy)- Gain one or more complete sets of chromosomes

- Nondisjunction- Primary cause of aneuploidy, failure of homologous chromosomes in meiosis 1 or sister chromoatids in meiosis 1 or 2 to separate correctly

- Trisomy- Gain of one chromosome (2n+1)

- Monosomy- Loss of one chromosome (2n-1)

- Tetrasomy- Gain of a pair of chromosomes (4) (2n+2)

- Nullisomy- Loss of a pair of chromosomes

- Autopolyploidy- occurs when the extra chromosome sets originate from the same species, can occur through failure of meiosis and mitosis.

- Triploidy- Three complete sets of chromosomes, sterile in plants lethal in humans.

- Tetraploidy- Four complete sets of chromosomes, often advantageous in plants and common.

- Unbalanced chromosomal rearrangements- Change in the total amount in genetic material through deletion or duplication

- Balanced chromosomal rearrangements- Rearrangement of existing material through inversion and translocation.

- Gene balance- h

Concepts

- Why are chromosomal mutations important?- can be insight into how genes act on genomic scale, reveal several important features of meiosis and chromosome architecture, experimental stuff, insight into evolutionary process, chromosomal mutations cause genetic disease.

- What is the primary cause of aneuploidy?- nondisjuction.

- Explain nondisjunction, what happens, and when it occurs- nondisjuction is when the homologous chromosomes or sister chromatids fail to separate correctly. (More common in meiosis 1)

- What are monosomics? Detail how it affects autosomes and the X chromosome? Also detail Turner syndrome (what it is, karyotype, and causes)- Monosomic is when there is a copy of a chromosome missing. For autosomes, monosomics die in miscarrage. In X- chromosomes they also die in utero BUT some are viable but have things like Turner syndrome.

- What are trisomics? What effect does it have on the offspring? Also explain Klinefelter syndrome (What it is, karyotype, and causes)- Trisomics have an extra chromosome. It can result in abnormalities or death. Klinfelter syndrome is a sex chromosome aneuploidy that affects males (extra X chromosome so XXY)

    Karyotype: 44;XXY (47 total chromosome)

    Cause: nondisjunction during the formation in an egg or sperm

- Detail Down syndrome (trisomy 21). Include the karyotype and cause.- Down syndrome is the most common aneuploidy in humans and its the presence of an extra full or partial copy of chromosome 21

    Karyotype: 45; XY/XX +21 (47 total chromosomes)

    Causes: nondisjunction in chromosome 21 during meiosis in the formation of gametes, also     is related to maternal age

- Detail the 3 genetic causes of Down syndrome-

    Trisomy 21 (95%)- each cell has three separate copies of chromosome 21

    Translocation (3%)- extra part or whole chromosome 21 is attached onto another     chromosome (usually chromosome 14) (Can only be inherited from a parent who is a     carrier)

    Mosaic (2%)- rare form where only some cells have the extra chromosome 21

- Explain Autopolyploidy. Include the mechanisms that can occur.- Autopolyploidy occurs when the extra sets originate from the same species and can occur through failure of meiosis (homologous chromosomes fail) or a failure in mitosis (all chromosomes fail)

- Detail Allopolyploidy. Detail why it generally causes offspring to be sterile- Allopoluploidy is when an organism processes multiple complete sets of chromosomes derived from different species, that results in a hybrid which is often sterile because the chromosomes inherited are homeologous (NOT homologous) so they don’t pair properly

- What are unbalanced chromosomal rearrangements? Detail the two main types- This is a change in the total amount of genetic material so new material. This includes deletion of a chromosome segment and duplication of a chromosome segment

- What are balanced chromosomal rearrangements? Detail the two main types- This is a rearrangement of existing material so NO new material. This includes inversion where segments within a chromosome can be reversed. Translocation is movement of a segment to a different chromosome.

- Compare and contrast terminal deletion and interstitial deletion- These are types of unbalanced chromosomal rearrangements where the material is deleted. Terminal deletion is loss of a segment at the end of the chromosome and Interstitial deletion is the loss of a segment internally on the chromosome.

- What are the consequences of chromosomal deletions?- Three consequences

    Happloinsufiency- deleted region may contain a gene where only one copy of it is not         enough

    Pseudodominance- If the deleted segment includes the dominant allele, the recessive alle     will also be expressed

    Seveity- severity of the effect depends on the size of the deletion and the specific genes     located on the segment (large deletions are usually lethal)

- Detail Cri-du-chat syndrome (what it is, karyotype, and causes)- This is cause by loss of genetic material from the end of the short arm of chromosome 5

    Karyotype- 44; XX or XY, del(5p)

    Causes- Spontanous deletion in gamete formation or in early fetal development is the most     common but it can be inherited.

- Compare and contrast tandem duplications, reverse tandem duplications, and displaced duplications- They all are a duplication of a segment on a chromosomes which results in extra genetic material

    Tandem Duplication- located immediately adjacent to the original segment

    Reverse Tandem Duplication- Segment is flipped but still adjacent to the original segment

    Displaced Duplication- located in a different location on the same or a different chromosome

- What are the consequences of chromosomal duplications

Gene Dosage Imbalance- the extra copy of genes disrupts the normal stoichiometry of gene prodicts

Phenotypic Effect- duplications can lead to abnormalities

Evolutionary Significance- duplications are an important in evolution

- Compare and contrast paracentric inversion and pericentric inversion-

Paracentric- the inverted segment does not include the centromere its on the chromosome

Pericentric- the inverted segment does include the centromere

- What are the consequences of chromosomal inversion-

Paracentric Inversion- produces an acentric fragment and a dicentric (two centromere) chromosome which leads to a non-viable zygote

Pericentric Inversion- produces chromosomes with both a duplication of one segment and deletion of another which results in a non-viable or a viable but severely affected child

- Compare and contrast reciprocal translocation and Robertsonian translocation- They both include movement of a segment to a different location

Reciprocal translocation- exchange of segments from two non-homologous chromosomes (results in two derivate chromosomes, still 46 chromosomes)

Robertsonian translocation- occurs between to acrocentric (centromere near one end) chromosome (only 45 chromosomes

- Detail the concept of gene balance- Its the fundamental principle that explains why changes in individual genes or chromosomes (gain or loss of a chromosome or chromosomal segments)

- Detail the stoichiometry of complexes in gene balance- This is where many cellular processes are mediated by multi-subunit protein complexes

- Explain the gene dosage effect- The synthesis of a gene product is generally directly proportional to the number of gene copies so 3 copies of a gene = 150% of the normal protein level

- Detail inverse dosage effect- Its used to cope with imbalances so if a cell is experiencing aneuploidy it often decreases the expression of genes located on other normal chromosomes

- Explain how chromosomal rearrangements can cause cells to become cancerous- It can disrupt Tumor suppressor genes and inactivate them