Chapter 15 Flashcards
law of segregation
the two alleles for each gene separate during independent assortment
law of independent assortment
alleles of genes on nonhomologous chromosomes assort independently during gamete formation
chromosomal theory of inheritance
states that Mendelian chromosomes have specific loci
o Also, it is the chromosomes that undergo segregation and independent assortment
wild type
red eyes (most common phenotype) found in drosophila (w+) o dominant trait
mutant type
traits that are alternative to the wild type
o w- white
X-Y system
sex of offspring depends on whether sperm cell contains X or Y chromosome
X-0 system
females have two x chromosomes (XX), males have one sex chromosome (X0)
• Sex is determined based on whether sperm carries X chromosome or no chromosome at all
• Grasshoppers, cockroaches, and beetles
Z-W system
sex chromosome present in egg, are either Z or W • Females- ZW • Males- ZZ • 76 chromosomes • Birds, fishes, and insects
Haplo-diploid system
females develop from fertilized eggs and are thus diploid, males develop from unfertilized eggs and are haploid (males have no fathers)
• Bees and ants
SRY
“sex-determining region of Y”
o In absence of this region, gonads develop into ovaries
sex-linked gene
gene located on either sex chromosome
Y-linked gene
genes located on Y chromosome
• Passed down by father
X-linked gene
genes found on the X chromosome
hemizygous
when a male lacks a recessive allele from his mother
o One or more genes that have no allelic counterparts???
Hemophelia
x-linked recessive disorder marked by absence in factors involved in blood clotting
o Bleeding can cause severe damage
o Results from mutation on X chromosome
Below… irrelevant?
o Almost all of one X chromosome is inactivated during female embryonic development
o Consequently, males and females have the same dose of X-linked genes
Barr body
inactive X chromosome in a female
o Lies along the inside of a nuclear envelope
o Reactivated in ovaries to give rise to eggs so that each female gamete has an active X
linked genes
genes located near each other on the same chromosome and which are inherited together
genetic recombination
the production of offspring with combinations of traits that differ from those found in either P generation parent
parental types
when the offspring inherit a phenotype that matches either of the phenotypes of the parental (P) generation
recombinant types/recombinants
offspring with new combinations of phenotype
o Results from random orientation of homologous chrom. at metaphase I of meiosis which leads to independent assortment of 2 unlinked genes
crossing over
process that breaks the physical connection between specific alleles of genes on the same chromosome
o Accounts for recombination of linked genes
genetic map
an ordered list of the genetic loci along a particular chromosome
Sturtevant’s hypothesis
o Stated that the recombination frequency depends on the distance between genes on a chromosome
o Assumed crossing over was a random event
o Predicted that the farther two genes are, the higher the probability that a crossover will occur between them and therefore, the higher the recombination frequency
recombination frequency
likelihood of recombination?
o The maximum value is 50% and occurs when two genes on a chrom. are so far apart crossover is basically guaranteed
• At this point, the genes are still considered genetically unlinked and assort independently (as if they were on different chromosomes).
