Chapter 7 Flashcards
Principle of segregation:
Alleles separate during
meiosis (one allele passed into each gamete)
Independent assortment
Alleles at one locus sort
independently from alleles at another locus
Independent separation of alleles results in
Recombination
Alleles sort into new combinations
Crossing over results in recombination:
it breaks up the associations
of genes that are close together on the same chromosome.
Linkage
keeps particular genes together while crossing over mixes
them up, producing new combinations
We must know not only the genotype but
also
the arrangement of genes on the
chromosomes (Horizontal lines represent
two homologous
chromosomes)
If genes are unlinked,
the heterozygous plant
produces
4 types of
gametes; two
nonrecombinant
(original combinations)
and two new
combinations
Nonrecombinant gametes –
contain only original
combinations of alleles that were present in the parents
Nonrecombinant progeny
display the original combinations
of traits present in the P generation
Recombinant gametes
new combinations of alleles
Recombinant progeny
Recombinant progeny –new combinations of traits
Crossing over Between Linked Genes
Valuable for genetic variation in meisos
Crossing over is typical between genes that lie on the same
chromosome.
– Producing new combinations of traits
– Remember, takes place in Prophase I of meiosis.
Linked Genes with Crossing Over
If height and leaf type are linked genes,
and NO CROSSING OVER occurs:
All four gametes produced are
nonrecombinants
If height and leaf type are linked genes,
and crossing over occurs:
Two of the four gametes produced are
recombinants
Recombination frequency =
(Number of
recombinant progeny/Total number of
progeny) x 100%
Coupling (cis configuration):
One chromosome contains
both wild-type alleles, one chromosome contains both
mutant alleles
