10.4 Study Guide Flashcards
Define chromosome disjunction. Define and explain the two primary consequences of chromosome disjunction.
Chromosome disjunction is the improper separation of chromosomes during meiosis. It causes gametes and, in turn, zygotes to have atypical numbers of chromosomes. The two primary consequences of this are trisomy, when a zygote has 3 copies of a chromosome instead of 2, and monosomy, when a zygote has 1 copy of a chromosome instead of 2.
Explain the difference between autosomes and sex chromosomes. What defines sex chromosomes?
Sex chromosomes are specifically the chromosomes that typically determine the sex a zygote will develop into. Autosomes are all the other chromosomes that are not sex chromosomes and do not determine sex.
Define Barr bodies. What is their purpose? How do trisomal and monosomal zygotes differ in their amounts of Barr bodies?
Barr bodies are extra X sex chromosomes that have been condensed and inactivated so as to inhibit any gene expression from them. Zygotes with multiple X chromosomes only need to express one, and thus must inactivate any and all others to prevent over-abundance of certain proteins during development. Typical XX zygotes as well as trisomal zygotes with two Xs will have one Barr body, trisomal XXX zygotes will have two Barr bodies, and monosomal X and trisomal XYY zygotes will have none.
Explain what occurs as a result of the different types of chromosomal abnormalities. What happens to zygotes when these abnormalities occur?
Deletion: The unnatural removal of a gene or gene sequence; produces zygotes with missing genes and possibly inadequate concentrations of certain proteins during development.
Duplication: The unnatural addition of a gene or gene sequence that is already present in the chromosome; produces zygotes with extra genes and possibly over-abundant concentrations of certain proteins during development.
Inversion: The unnatural reversal of the order of a gene sequence; potentially inhibits future pairing of homologous chromosomes during meiosis I (may produce sterility).
Translocation: The unnatural swapping of genes or gene sequences between different types of chromosomes; may produce zygotes with too many or too few proteins, like with deletion and duplication, or may produce inconsequential changes.
Fill in the blanks:
A zygote with a set of XY sex chromosomes will typically develop a _____ reproductive system and will contain _____ Barr body(ies).
A zygote with a set of XXY sex chromosomes will typically develop a _____ reproductive system and will contain_____ Barr body(ies).
A zygote with just one X sex chromosome will typically develop a _____ reproductive system and will contain _____ Barr body(ies).
- A zygote with a set of XY chromosomes will typically develop a male reproductive system and will contain 0 Barr bodies.
- A zygote with a set of XXY sex chromosomes will typically develop a male reproductive system and will contain 1 Barr body.
- A zygote with just one X sex chromosome will typically develop a female reproductive system and will contain 0 Barr bodies.
State the chromosomal abnormalities found in each of the following chromosomes:
ABCDEFG –> ABCDEDEG
AGDEBCHF –> AGDECBHF
BFAHDGEC –> BFAHDGC
- Duplication of DE and Deletion of F
- Inversion of BC
- Deletion of E
In a karyotype with an unnaturally long copy of Chromosome 15 and an unnaturally short copy of Chromosome 22, what chromosome abnormality has occurred?
Translocation between the two chromosome copies has occurred.
True or False: A karyotype with XXY sex chromosomes has trisomy and will typically code to produce a female reproductive system.
False, a karyotype with XXY sex chromosomes has trisomy and will typically code to produce a male reproductive system due to the presence of a Y sex chromosome.
