Linkage and chromosomes Flashcards
(26 cards)
Law of separation?
Anaphase 1 - separation of homologs accounts for the segregation of the 2 alleles of a gene into seperate gametes
Law of independent assortment?
Metaphase 1 - A random arrangement of chromosome pairs accounts for independent assortment of alleles for 2 or more genes located on different homolog pairs.
Hemizygous?
Men have only 1 locus for a X-allele
X-inactivation?
The X-chromosome becomes inactivated forming a Barr body and females consists of a mosaic of 2 types of cells - active from father and active from mother - all mitotic descendants of that cell will recieve the same Barr body and one XIST.
Linked genes?
Genes located near each other on the same chromosome tend to be inherited together in genetic crosses.
2 or more genes on the same chromosome that tend to be inherited together.
Sex-linked genes?
Single gene on a sex chromosome
Non-parental phenotypes?
Combinations of traits not seen in P-generation
Genetic recombination?
Production of offspring with combinations of traits that differ from the P-generation.
Sexually reproductive offspring -
Independent assortment of chromosomes
Crossing over
Possibility of any sperm fertilizing an egg
Recombination of unlinked genes?
Combinations of traits that do not match the P-generation. A 50% RF is obeserved for any 2 genes that are located on different chromosomes and cannot be linked because of the independent assortment of the 2 unlinked genes during meiosis.
Recombination of linked genes?
Occurence of parental types with a RF of less than 50% = genes are linked.
The effect comes from crossing over in the prophase 1 where corresponding segments of 1 maternal and 1 paternal chromatid
A single crossover?
End portions of 2 non-sister chromatids trades place.
RF?
Recombinants / Total offspring x 100 = %
Reflects combinations of alleles not seen before in either P-generation.
Genetic map?
An ordered list of the genetic loci along a chromosome
RF and Mapping?
The D between genes on chromosomes - the farther apart 2 genes are the higher the probability that a crossover will occur between them = higher RF
The longer D between 2 genes the more points there are between them where crossing over can occur
Because if they are close = they would follow during a crossover since 2 segments exchange between 1 paternal and 1 maternal.
Linkage map?
A genetic map based on RF 1 mu = 1% and gives a good approximation since it is only based on RF and can portray an order of genes along a chromosome but not precisely the the loci of genes.
Non-disjunction?
Members of a pair of homologs do not move apart during meiosis or sister chromatids fail to separate.
1 gamete recieves 2 of the same chromosome and 1 no copy.
Aneuploidy?
Abnormal number of chromosomes.
Monosomic or trisomic
Polyploidy?
2 or more complete chromosomes in somatic cells.
Triploidy - 3n = 3 sets
Tetraploidy - 4n = 4 sets
Alternations of chromosome structure?
Errors in meiosis can cause breakage of chromosomes
Deletion?
Chromosomal fragment is lost
Duplication?
The deleted segment may become attached as an extra segment to a sister chromatid or non-sister chromatid
Inversion?
A fragment can reattach to the original chromosome but in reverse orientation
Translocation?
A fragment joins a non-homologous chromosome
Deletion and duplication?
Likely to happen during meiosis
Crossing between non-sister chromatids that exchange unequal sized segments of DNA = 1 partner recieves more than it recieves
