Pages 266-271, 274 Flashcards
Sutton and Boveri
each realized that meiosis could account for Mendel’s rules.
Locus
particular position along a chromosome where a gene is located.
The physical separation of alleles during anaphase of meiosis I is responsible for
Mendel’s principle of segregation.
If the alleles for different genes are located on different chromosomes
they assort independently of one another at meiosis I. this is the physical basis of Mendel’s principle of independent assortment.
Chromosome theory of inheritance
states that Mendel’s rule can be explained by the independent alignment and separation of homologous chromosomes at meiosis I.
Wild type
most common phenotype for each trait.
Mutation
heritable change in a gene.
Mutant
individual with a phenotype due to a mutation.
X-linked inheritance (X-linkage)
gene residing on the X chromosome.
Y-linked inheritance (Y-linkage)
gene residing on the Y chromosome.
Sex-linked inheritance (sex-linkage)
general term for inheritance of genes on either sex chromosome.
When reciprocal crosses give different results,
it is likely that the gene is located on a sex chromosome – it is sex-linked.
Autosomal inheritance
genes on non-sex chromosomes.
The discovery of X-linked inheritance convinced most biologists that
the chromosome theory of inheritance of correct.
linkage
the tendency of particular alleles of different genes to be inherited together. Seen when genes are on the same chromosome.
recombinant
combination of alleles on the X chromosome is different from the combinations of alleles present in the mother.
To explain the recombinant phenotypes, Morgan proposed that
gametes with new combinations of alleles were generated when crossing over occurred during prophase of meiosis I in the females.
The percentage of recombinant offspring that occur in crosses can be used
to estimate the relative distance between genes.
The farther genes are apart on the same chromosome
the more likely it is that a crossover will occur someplace between these genes.
genetic map
diagram showing the relative positions of genes along a particular chromosome. Can be created from data on the frequency of crossing over between many genes on the same chromosome.
Linked genes are inherited together unless
crossing over occurs between them. When crossing over takes place, genetic recombination occurs.
Crossing over is rare between
genes that are close together.
Calculate the recombinant frequency
as the number of offspring with recombinant phenotypes divided by the total number of offspring.
Sturtevant
proposed that the physical distance between genes determines how frequently crossing over occurs between them.
1 centiMorgan (cM)
physical distance that produces 1 percent recombinant offspring.
