Genetics Chapter 8 Flashcards
Deletion (aka deficiency)
phenotypic consequences of deletions depend on its size and genome content
Terminal deletion
single break, usually at the end
Interstitial deletion
2 breaks and reattachment of the outer pieces
Example: cri-du-chat syndrome in humans
Caused by a deletion in the short arm of chromosome 5
(CTNND2/delta-catenin is deleted), affected individuals have more severe intellectual disability
Duplication
tend to have less harmful effects than deletions
Usually caused by abnormal events during recombination
Inversion
is a segment that has been flipped to the opposite orientation
Total amount of genetic information stays the same
Pericentric inversion(left)
the centromere within the inverted region
During meiosis I, homologous chromosomes synapse with each other in an inversion loop
Paracentric inversion(right)
the centromere is outside of the inverted region
In rare cases, inversion can alter the phenotype of an individual
Consequences of inversion
Breakpoints
Position effect: a gene that is repositioned in a way that alters its gene expression
Simple translocations
single piece of chromosome is attached to another chromosome
Reciprocal translocations
2 non-homologous chromosomes exchange genetic material
Leads to a rearrangement of the genetic material, not a change in the total amount, thus it is also called balanced translocation
Mechanism 1: chromosomal breakage and DNA repair
Mechanism 2: nonhomologous recombination
Just like inversions, they are usually WITHOUT PHENOTYPIC CONSEQUENCES!!
Unbalanced Translocations
significant positions of genetic material are duplicated and/or deleted
Usually WITH phenotypic abnormalities or even lethality
Robertsonian translocation
most common type of chromosomal rearrangement in humans
Majority of chromosome 21 is attached to chromosome 14
Individuals with reciprocal translocation may produce
abnormal gametes
Balanced translocation have a greater risk of producing gametes with
UNBALANCED COMBINATIONS OF CHROMOSOMES
What must happen for a chromosome to synapse properly?
TRANSLOCATION CROSS MUST FORM
Mitotic segregation of chromosomes with reciprocal translocation
Alternate segregation: viable-balance
Chromosomes on opposite sides of the translocation cross segregate into the same cell
Adjacent-1 segregation: inviable-unbalanced:
Adjacent non-homologous chromosomes segregate into the same cell-both have duplications/deletions
Adjacent-2 segregation: inviaible-unbalanced
Adjacent homologous chromosomes segregate into the same cell-both have duplications and deletions
RARE
When is it likely for alternate and adjacent-1 segregation outcomes?
When an individual carries a RECIPROCAL TRANSLOCATION
With reciprocal translocation, it usually produces 4 types of gamete
2 are viable & 2 nonviable
This condition is called SEMISTERILITY
Explain what a karyotype is and what it can be used for
Karyotype: using a light microscope, it checks the chromosomes in our cells
Can observe if we have the full set of 46 chromosomes
Checks for diseases such as down syndrome, turner syndrome etc
Metacentric
centromere is at the middle, equal p & q length
Acrocentric
centromere located at the end of the chromosome
Telocentric
centromere is in a terminal position
Submetacentric
centromere is NEAR the middle, p and q are slightly uneven
p=short arm
q=long arm
Explain what chromosome banding patterns are and what they can be used to study
Staining revealing bands
Example: Giemsa stan-G band
Stains of bright and dark transverse bands
Bands identify where the genes are located on a chromosome
Aneuploidy
variation in the number of particular chromosomes within a set
