Biology Questions and Answers
Linkage and
Crossing Over
- Why is not Mendel’s second
law always valid for two or
more phenotypical traits of an
individual?
Mendel’s second law, oindependent assortment, is valid r the law of forthe
genes located These genes during meiosis sein different chromgregateosomes.
independently.
Mendel’s second law however is not
valid for phenotypicalconditioned by genes located featuresin the (^)
same chromosome (genes under
linkage), since thlinked genes, do not separate iese genes, known asn meiosis (^)
(except for the phenomenon of crossing
over).
- Why is drosophila a
convenient animal for the
study of linked genes?
The fruit fly drosophila is suitable for the
study of Genetics because it pmany distinct traits but only fourresents
chromosomes (and three autosomone sex chres). omosome
- What is linkage?
Two genes are said to be under linkage,
or linked, when they chromosome. reside in the same
For examplgenome discovere, the research oed that the factor III off the human
clotting ggene are locateene and the factor V od in the same f clotting
chromosome (the human chromosome
1). The factor Vlinked to those genes since itII gene however is not is located (^)
in the chromosome 13.
- What is crossing over? How
is meiosis related to this
phenomenon?
Linked alleles, foB, form the gametes A-br example, A-b and a-B that and a-
maintain type of linkagthe linkage e is called of the alleles. Thiscomplete
linkage. In the first division of meiosis
(meiosis I) however the crossing phenomenon may occur. Chromosomesover (^)
from a pexchange extremities anair of homologous mayd some (^) once
linked alleles, for example, A-b and a-B,
recombinthe case, A-B ane to form different gamd a-b. etes, in
Crossing ovarms of the chromatids oer may happen when thef each
homologous are paired during meiosis.
Matchintwo nonsister chrg portions oomatidsf the extremities (one from one of (^)
homologous of the pair) break and the
pieces arbecoming part of the arm of e exchanged, each of themthe other (^)
chromatid. For example, if the allele A is
situated the point of breaking and the allele b isin a side of the arm relating to (^)
http://www.biology-questions-and-answers.com