Chapter 15: THe Chromosomal Theory of Inheritance (4)

The phenotype of an organism can be affected by small-scale changes involving individual genes. __ are the source of all new alleles, which can lead to new __ traits.

Large-scale chromosomal changes can also affect an organism's __. Physical and chemical disturbances, as well as errors during meiosis, can damage chromosoems in major ways or alter their number in a cell.

Large-scale chromosomal alterations often lead to spontaneous __ of a fetus, and individuals born with these types of genetic defects commonly exhibit various developmental disorders.

TRUE OR FALSE:
In plants, such genetic defects may be tolerated to a greater extent than in animals.
-- Ideally, the meiotic spindle distributes chromosomes to daughter cells without error. But there is an occasional mishap, called a __, in which the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II.
---- In these cases, what happens to the gametes?
True False

If either of the aberrant gametes unites with a normal one at fertilization, the zygote will also have an abnormal number of a chromosome, called __. (It may involve more than one chromosome.)

Fertilization involving a gamete that has no copy of a particular chromosome will lead to a missing chromosome in the zygote (2n-1); the __ zygote is said to be __ for that chromosome.

If a chromosome is present in triplicate in the zygote (2n+1), the __ is __ for that chromosome.

Mitosis will sunsequently transmit the __ to all embryonic cells. If the organism survives, it usually has a set of traits caused by the abnormal dose of the genes associated with the extra or missing chromosome.
-- __ is an ex. of trisomy in humans.

__ can also occur during mitosis. If such an error takes place early in embryonic development, then the __ condition is passed along by mitosis to a large number of cells and is likely to have a substantial effect on the organism.

Some organisms have more than two complete chromosome sets in all somatic cells, called __. (3n= __/ 4n= __)
A __ may arise by the fertilization of an abnormal diploid egg produced by nondisjunciton of all its chromosomes.
__ could result from the failure of a 2n zygote to divide after replicating its chromosomes.
Subsequent normal mitotic divisions would then produce a 4n embryo.

__ is fairly common in the plant kingdom. (Bananas are __ and wheat is __.)
In the animal kingdom, __ are much less common, although they are known to occur among fishes and amphibians.
In general, __ are more nearly normal in appearance than __.

One extra or missing chromosome apparently disrupts genetic balance more than does an entire extra set of chromosomes.
Errors in meiosis or damamging agents such as __ can cause breakage of a chromosome, which can lead to four types of changes in chromosome structure: __, __, __, and __.

A __ occurs when a chromosomal fragment is lost. The affected chromosome is then missing certain genes. (If the affected __ is deleted, the entire chromosome will be lost.

The deleted fragment may become attached as an extra segment to a sister chromatid, producing a __. ALternatively, a detached fragment could attach to a nonsister chromatid of a homologous chromosome. In that case, though, the __ segments might both be identical beacuse the homologs could carry different alleles of certain genes.

A chromosomal fragment may also reattach to the original chromosome but in the reverse orientation, producing an __.

A fourth possible result of chromosomal breakage is for the fragment to join a nonhomologous chromosome, a rearrangement called __.

__ and __ are especially likely to occur during meiosis. In crossing over, nonsister chromatids sometimes exchange unequal-sized segemts of DNA, so that one partner gives up more genes than it receives. The products of such a __ crossover are one chromosome with a __and one chromosome with a __.

A diploid embryo that is homozygous for a large __ (or has a single X chromosome with a large deletion, in a male) is usually missing a number of essential genes, a condition that is ordinarily lethal.
__ and __ also tend to be harmful.
In __, in which segments are exchanged between __, and in __, the balance of genes is not abnormal- all genes are present in their normal doses. Nevertheless, __ and __ can alter phenotype because a gene's expression can be influenced by its location among neighboring genes' such events sometimes have devastating effects.

Alterations of chromosome number and strucure are associated with a number of serious human disorders. (__ in meiosis results in __ in gametes and any resulting zygoes.) However, some types of __ appear to upset the genetic balance less than others, with the result that individuals with certain __ conditions can survive to birth and beyond.
-- These individuals have a set of traits- a __- characteristic of the type of __. Genetic disorders caused by __ can be diagnosed before birth by fetal testing.

One aneuploid condition, __, affects approx. one of every 700 children born in the US; result of an extra chromosome 21 (total of 47 chromosomes. Because the cells are __ for chromosome 21, it is often called __; characteristic facial features, short stature, heart defects, susceptibility to respiratory infection, and mental retardation; prone to develop leukemia nad Alzheimers

Frequency of __ increases with mom's age. While the disorder occurs in just __ of children born to women under age 30, the risk clims to __ for mothers at 40 and even higher for older moms.
- Most cases result from __ during meiosis I, and some research points to an age-dependent abnormality in a meiosis checkpoint that normally delays __ until all kinetochores are attached to the spindle. __ of some other chromosomes also increase in incidence with maternal age, although infants with other autosomal trisomies rarely survive for long.

__ of sex chromosomes produces a variety of aneuploid conditions. Most of these conditions appear to upset genetic balance less than __ conditions involving autosomes. This may be because the _ chromosome carries relatively few genes and becasue extra copies of the __ chromosome become inactivated as __ in somatic cells.

An extra X chromosome in a male, producing __, occurs approx. once in every 2000 live births. People with this disorder, called __, have male sex organs, but the testes are abnormally small and the man is sterile.
- Even though teh extra X is __, some breast enlargement and other femal ebody characteristics are common.

Males with an extra Y chromosome (__) do not exhibit any well-defined syndrome, but they tend to be somewhat taller than average.

Females with __ X (__) which occurs once in approx. 1000 live births are healthy and cannot be distinguished from XX females except by karyotype.
__ X, called __, occurs about once in every 5000 births and is the only known viable monosomy in humans.

Although these __ individuals are phenotypically female, they are sterile because their sex organs do not mature. When provided with estrogen replacement therapy, girls with __ do develop secondary sex characteristics. Most have normal intelligence.

Many __ in human chromosomes, even in a heterozygous state, cause sever problems.
- One such syndrome, such as _-, results from a specific __ in chromosome facial features, and has a cry that sounds like a distressed cat. These people usually die in infancy or early childhood.

Chromosomal __ have been implicated in certai cancers, including __.
- This disease occurs when a reciprocal transloccation happens during mitosis of cells that will become WBCs. In these cells, the exchange of a large portion of chromosome 22 with a small fragment from a tip of chromosome 9 produces a much shortened, easily recognized chromosome 22, called __.