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Chapter 15
Chromosomal Basis of Inheritance
| Question | Answer |
|---|---|
| P generation | specificying seed color; two genes are on different chromosomes |
| F1 Generation | Law of Segregation and Law of Independent Assortment |
| Law of segregation | the two alleles for each gene separate during gamete formation |
| law of independent assortment | alleles of genes on nonhomologous chromosomes assort independently during gamete formation |
| wild type | the phenotype for a character most commonly observed in natural populations |
| mutant phenotypes | traits that are alternatives to the wild type because they are due to alleles assumed to have originated as changes, or mutations in the wild-type allele. |
| How is sex determined? | chromosomes |
| short segments at either end of the Y chromosome are the only regions that are ___ with regions on the X. | homologous |
| What is required for the development of testes? | SRY (sex-determining region of Y) |
| sex-linked gene | a gene located on either sex chromosome |
| What happens when there are so few Y linked genes? | very few disorders are transferred |
| What gene is required for the female gonads? | WNT4 (chromsome 1, an autosome); encodes protein for ovary development |
| If an X-linked trait is due to recessive allele, a female will express the phenotype only if she is __ for the allele | homozygous |
| barr body | the inactive x in each cell of a female condenses into a compact object which lies within nuclear envelope. |
| if a female is heterozygous for a sex-linked trait, about half of her cells will express one allele while the others will express the __ allele | alternate |
| genetic recombination | the production of offspring with combinations of traits that differ from those found in either P generation parent. |
| What can be genetically unlinked? | genes assort indepedently , as if they are on different chromosomes |
| Large-scale chromosome | -affect organisms phenotype -meiosis error -disorders -abortion |
| What distributes meiotic spindle without error? | daughter cells |
| nondisjunction | members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to seperate during meiosis II. |
| What happens in nondisjunction? | one gamete receives two of the same type of chromosome and another gamete receives no copy |
| aneuploidy | if aberrent gametes unites with a normal one at fertilization, zygote will have an abnormal number of a particular chromosome. |
| What are the four types of changes that can alter chromsome structure? | -deletion -duplication -inversion -translocation |
| deletion | chromosomal fragment is lost |
| duplication | "deleted" fragment may become attached as an extra segment to a sister or nonsister chromatid |
| inversion | chromosomal fragment may reattach to the original chromosome but in the reverse orientation |
| translocation | fragment to join a nonhomologous chromsome, a rearrangement |
| genomic imprinting | such variation in phenotype depending on whether an allele is inherited from the male or female parent |
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