Genetics: Chromosome Abnormalities

What are the three human chromosomes that can be trisomic in liveborns? Which is the most common among the three?

13,18,21 Most common is trisomy 21 (down syndrome)

Define aneuploidy and polyploidy and know the difference.

Anueploidy- presence of one or more chromosomes or absence of Polyploidy-an extra chromosome set, germline events rare

Compare phenotypic consequences of deletions and inversions. Which are more severe? Why?

Deletions are more severe since you are losing genes

Name the main categories of structural aberrations that can occur in mammalian chromosomes.

Deletions, duplications, inversions, translocations

Cite and explain one possible reason for the trisomy 21 disorder. Name the syndrome.

Down Syndrome chromosome 21 carries tumor suppressor genes***

Give an example of a human genetic disorder associated with fragile sites. Explain its mechanism

Fragile X syndrome caused by expansion of trinucleotide repeats in the FMR1 gene (CGG) that silences this gene

What type of translocations has generated the Philadelphia chromosome?

HSA9/22 reciprocal translocation

Which germline events can lead to human polyploidy?

Mitotic failure in embryogenesis(tetraploid) Cell fusion (tetraploid) Egg fertilized w/ 2 sperms (triploids) Ovum fused w/ polar body when fertilized (triploids) Meiosis I or II errors (triploids)

What are paralogous genes? Give an example.

Paralogous genes are genes in the same species that resulted from gene duplications that share some sequence similarity but have distinct gene products and functions Ex. Gamma globins and Milk caseins

Name the two main types of translocations

Reciprocal- both chromosomes gain and lose genetic material. Nonreciprocal- one chromosome gains genetic material while the other loses it

Spontaneous abortions with trisomy of chromosome 1 or chromosome 19 are never seen. Do they ever occur? Explain.

They never occur because the areas are too gene dense for it to even get started

Why are autosomal numerical aberrations less tolerated by the cell/organism than aberrations in the number of sex chromosomes?

abberations of the sex chromosome are more tolerable b/c of x inaction, and low number of genes on Y? *****

Why do chromosomal aberrations lead to disease and disorders?

can affect regulatory regions and gene functiond

What kind of translocation is called 'Robertsonian translocation'?

fusion of two arcocentric chromosomes

Why is autosomal trisomy more tolerated when it happens in small chromosomes than when it happens in large chromosomes

it affects less genes than a larger area

What is a deletion and what are the consequences of this aberration?

loss of any genetic material from a single locus to larger segments consequences include loss of genes, problems in meiotic pairing, changes in phenotype

Trisomy for many different chromosomes is routinely observed in spontaneous abortions, but monosomy is not. Why?

monosomic zygotes die before implantation so there is no recognized pregnancy

What is the fundamental difference between deletions/duplications and inversions?

no loss or addition of genetic material in inversions

What kind of mistake in cell division can lead to XYY aneuploidy?

non disjunction of sister chromatids in sperm

What is the role of duplications in evolution?

overdose of genetic material problems in meiotic pairing changes in phenotype

What are the consequences of numerical aberrations in sex chromosomes for the organism?

subfertility or infertility mild mental or physical problems

Name the main consequences of duplications.

unequal crossing over in meiosis overdose of genetic material phenotypic variation