Chapter 15 Flashcards
Chromosome theory of inheritance
Mendelian genes have specific locations along chromosomes, and it is the chromosomes that undergo segregation and independent assortment
A specific gene is carried on a specific chromosome
Females have… Males have…
Homologous X chromosomes
One X and one Y
Wild type
The phenotype for a character most commonly observed in natural populations
Mutant phenotypes
Traits that are alternatives to the wild type
They are due to alleles assumes to have originated as changes/mutations
Each egg receives
One chromosome
The Y chromosome is much smaller than
The X chromosome
Sperm receives
Half of sperm receives X chromosomes and the other half receives Y chromosomes
Sex-linked gene
A gene located on either sex chromosome
Y-linked genes
Genes located on the Y chromosome
X-linked genes
Genes located on the X chromosome
Hemizygous
Describes X-linked genes
Instead of hetero and homo
Any male receiving the recessive allele from his mother will
Express the trait
The cells of females and males have
The same effective dose (one copy) of most X-linked genes
Barr body
The inactive X in each cell of a female condenses into a compact object
Lies along the inside of the nuclear envelope
Most of the genes of the X chromosome that forms the Barr body are
Not expressed
Females have a mosaic of two types of cells
Those with the active derived from the father and those with the active derived from the mother
After an X chromosome is inactivated
All mitotic descendants of that cell have the same inactive X
The number of genes in a cell is
Greater than the number of chromosomes Each chromosome (except Y) has hundreds or thousands of genes
Linked genes
Genes located near each other on the same chromosomes end to be inherited together in genetic crosses
Genetically linked
Genetic recombination
The production of offspring with combinations of traits that differ from those found in either P generation parent
Parental types
Inherit a phenotype that matches either of the phenotypes of the P (parental) generation
Matching offspring
Recombinant types (recombinants)
Nonparental phenotypes
New combinations
Crossing over
Breaks the physical connection between specific alleles of genes on the same chromosome
Accounts for the recombination of linked genes
Occurs while replicated homologous chromosomes are paired during prophase of meiosis I
A set of proteins orchestrates an exchange of corresponding segments of one maternal and one paternal chromatid
Each pair of homologous chromosomes lines up independently of other pairs during metaphase I, and crossing over prior to that, during prophase I, can
Mix and match parts of maternal and paternal homologs
Genetic map
An ordered list of the genetic loci along a particular chromosome
The farther apart two genes are,
The higher the probability that a crossover will occur between them and therefore the higher the recombination frequency
The greater the distance between two genes,
The more points there are between them where crossing over can occur
Linkage map
A genetic map based on recombination frequencies
Map units
Distance between genes
Despite being on the same chromosome and being physically connected,
The gees are genetically unlinked; alleles of such genes assort independently, as if they were on different chromosomes
Nondisjunction
Occasional mishap
Members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II
One gamete receives two of the same type of chromosome and another gamete receives no copy
Other chromosomes are distributed normally
Aneuploidy
A condition… If either of the aberrant gametes unites with a normal one at fertilization, the zygote will also have an abnormal number of particular chromosomes
Monosomic
Fertilization involving a gamete that has no copy of a particular chromosome will lead to a missing chromosome in the zygote… called for that chromosome
Trisomic
If a chromosome is present in triplicate in the zygote… called for that chromosome
Polyploidy
More than two complete chromosome sets in all somatic cells
Deletion
Occurs when a chromosomal fragment is lost
Affected chromosome is missing certain genes
Duplication
Deleted fragment may become attached as an extra segment to a sister chromatid, producing…
Inversion
A chromosomal fragment may also reattach to the original chromosome but in the reverse orientation, producing…
Translocation
Fragment joins a nonhomologous chromsome, rearrangement called…
Genomic imprinting
Variation in phenotype depending on whether an allele is inherited from the male or female parent
Genomic imprinting occurs
During gamete formation and results in the silencing of a particular allele of certain genes
Not all of a eukaryotic cell’s genes are located on nuclear chromosomes, or even in the nucleus, some genes are located
In organelles in the cytoplasm
These genes are called extranuclear genes or cytoplasmic genes
