A form of aneuploidy where a mosaic individual forms at some point when one chromatid lags so far behind in anaphase that it is not incorporated into the daughter cell nucleus, thus having 1 less chromosome
Differentiate between balanced and unbalanced translocations
One part of a chromosome breaks off and incorporates onto another non-homologous chromosome at the centromere.
Balanced - subsequent gamete has all genetic material in one form or another
Unbalanced - subsequent gamete has extra or missing genetic material
At which point is something called a chromatid?
When the chromosomes have replicated, 2 sister chromatids are joined together at the centromere, then pulled apart in anaphase
At what points are things called chromosomes?
Individual ones in normal cell (46), pair of sister chromatids after replication (46 pairs), and separated chromatids in daughter cells (now chromosomes)
Describe chromosome nomenclature
Particular site on a chromosome?
23 chromosome pairs, 22 autosomal and 1 sex. Numbered from largest (1) to smallest (22 - actually 21). Two arms per chromosome, separated by centromere. p arm (petite) and q arm (next letter). Each arm divided into regions, each with a certain number of bands and sub-bands within bands.
16p11.1 = chrom. 16, p arm, region 1, band 1, sub-band 1
Which cell types are germ cells?
Cells that give rise to gametes (divide to make eggs and sperm)
What are homologous chromosomes?
Chromosome pair within a normal cell that contains 1 from mom and 1 from dad
Explain Karyotype nomenclature
Way of writing chromosome makeup of a cell
1. # of chromosomes
2. Sex chromosomes
3. Numerical abnormalities (+ and -)
4. Structural abnormalities
Ex. 46, XY+21, upd(15)mat
Different cells within an organism differ genetically from other cells due to early nondisjunction or anaphase lag
What is a somatic cell?
Any body cell other than a germ cell, gamete, gametocyte, or undifferentiated stem cell
What is genomic imprinting?
What is the clinical significance?
The differential activation of gene alleles on one homolog and not the other, thereby only expressing that gene from the maternal or paternal chromosome
If the one active allele is mutated or inactivated, there is no second allele to cover for it
What is nondisjunction?
Failure of two chromosomes (meiosis 1) or two chromatids (meiosis 2, mitosis) to separate into opposite daughter cells during anaphase.
What are the main consequences that can result from nondisjunction? (Meiosis 1 vs meiosis 2)
Which can lead to mosaicism?
Meiosis 1 - 1/2 gametes are trisomic after fertilization, 1/2 are monosomic after fertilization (fatal)
Meiosis 2 - 1/2 are euploid after fertilization (normal), 1/4 trisomic, 1/4 monosomic (fatal)
Meiosis 2 (some normal, some trisomic)
What is uniparental disomy?
Trisomy in which trisomy recovery removes the single chromosome from one parent, leaving 2 homologous chromosomes from the same parent
What is uniparental isosomy?
Trisomy rescue resulting in 2 identical copies of the same chromosome from the same parent (usually fatal)