Chapter 15 : The Chromosomal Basis Of Inheritance Flashcards
Chromosome Theory of Inheritance
Genes occupy specific positions on chromosomes, and it’s the random alignment of pairs of homologous chromosomes at the metaphase 1 and the separation of homologs in anaphase 1 that result in independent assortment and segregation of alleles in gamete formation.
The normal phenotype found most commonly in nature; represented by what
Wild type; a superscript
Alternative traits, assumed to have arisen as mutations
Mutant phenotypes
Females are XX, and produce eggs that each have an X chromosome. What are males?
Males are XY, and produce two kinds of sperm, each with either an X or a Y chromosome
Whether the gonads of an embryo develop into tested or ovaries depends on the presence or absence of what gene
SRY gene
Where is the SRY gene found
On the Y chromosome
Genes located on either sex chromosome are called :
Sex-linked genes
Approximately how many genes are located on the Y chromosome, and where are about half of these genes expressed?
78; in the testis
Approximately how many genes are located on the X chromosome?
1,100
From where do males inherit X-linked alleles
The mother
Where do daughters inherit X-linked alleles
Both parents
What condition is a result of a lack of a key muscle protein
Duchenne muscular dystrophy
What trait is characterized by excessive bleeding due to the absence of one or more blood-clotting proteins
Hemophilia
After X inactivation, the other X chromosome is contracted into the Barr body. Where is this located?
Inside the nuclear membrane
Both males and females having an equal dosage of most X-linked genes is a result of what
X inactivation
Is the selection of which X chromosome to be inactivated planned or a random event
Random event in embryonic cells
Genes located near eachother on the same chromosome tend to be inherited together. What are these called
Linked genes
Offspring with combos of traits that are different from those of either P generation parent is a result of what
Genetic Recombination
What is a genetic map
An ordered list of genes on a chromosome
Recombination frequency
Percentage of recombinant offspring produced in a genetic cross
What did A.H. Sturtevant suggest about recombination frequencies
That they reflect the relative distance between genes
Is the probability of crossing over occurring greater or lesser if the genes are farther apart
Greater
When does nondisjunction occur?
When a pair of homologous chromosomes does not separate properly in meiosis 1, or when sister chromatids do not separate in meiosis 2.
Sometimes a gamete receives either two copies or no copies of a chromosome. What is this a result of?
Non disjunction
A nontypical number of a particular chromosome
Aneuploidy
What is the chromosome number if a zygote is trisomic for that chromosome?
2n+1
What is the chromosome number if a zygote is monosomic for that chromosome?
2n-1
A chromosomal alteration in which an organism has more than two complete chromosomal sets (like triploidy or tetraploidy)
Polyploidy
Chromosome fragments that are lost
Deletion
When chromosome fragments join to a sister chromatid
Duplication
When chromosome fragments break off, join a sister chromatid, and rejoin the original chromosome in the reverse orientation
Inversion
When chromosome fragments break off, join a sister chromatid, then join a nonhomologous chromosome
Translocation
What is the difference between an organism with a trisomy and a triploid organism?
Trisomy means there is an extra chromosome (2n+1), but a triploid organism has a whole nother complete set of chromosomes.
What is Down syndrome also known as?
Trisomy 21
