chapter 12

Seite 1

12.1 Q/A

1) How is the work of Mendel and the work of Boveri and Sutton related?

Both men formed their hypothesis using Mendel's work as a basis, combined with improved Microscope technology to observe chromosomes.

2) What was Morgan's contribution to our understanding of heredity and why was it necessary?

He helped provide evidence supporting the idea that chromosomes are the basis for genetic inheritance.

3) Review the description of meiosis and Mendel's two principles. What is the physical basis for each of Mendel's principles?

The Law of Segregation: Each inherited trait is defined by a gene pair- in meiosis, gametes have 1/2 of the genetic information at the end and will only become a gene pair when they combine.

The law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another - In meiosis different parts of the genome code for different traits and they don't affect each other unless they are related.

Seite 2

12.2 Q/A

1) Explain why sex-linked diseases are more common in human males.

Cause if it's a trait linked to X, they only have 1 X chromosome and therefore lack the defense of needing 2 of the sex-linked disease trait that women have. Also if it is Y-linked (unlikely), then women cannot get it because they do not have Y chromosomes.

2) Predict the outcome of crosses that involve X-linked genes. Describe the inheritance patterns and symptoms of color blindness and hemophilia.

Women can be carriers, healthy or affected.

Men can either be Healthy or affected. No in-between.

3) In fruit flies, the gene for white eyes is sex-linked recessive. (R) is red and (r) is white. Cross a white-eyed female with a normal red-eyed male. What percent of the males will have red eyes? White eyes? What percent of the females will have red eyes? White eyes? What total percent of the offspring will be white-eyed? What percent of the offspring will be carriers of the white eye trait?

No females will have white eyes. All Males will have white eyes.

4) Describe the process of X inactivation in female mammals. Explain how this phenomenon produces calico coloration in cats.

X-inactivation in female mammals ensures that mammal females don't have twice as many X chromosome gene products as males, who have 1 X chromosome.

Calico cats are a result of this because they have their coloration determined by a sex-linked allele. Inactivation of one X allows for one X to completely determine the coloration of the female.

Seite 3

12.3 Q/A

1) Distinguish between linked genes and sex-linked genes.

Linked genes are genes that code for different things that are on the same chromosome, and the closer they are together the less likely you are to get a cross between parents.

Sex-Linked genes are genes that code for things that help determine things related to the sex of an organism.

2) Describe the independent assortment of chromosomes during meiosis I. Explain how an independent assortment of chromosomes produces genetic recombination of unlinked genes.

An Independent assortment of Chromosomes allows for the recombination of DNA for unlinked traits.

The independent assortment of chromosomes produces genetic recombination of unlinked genes because unlinked genes cannot affect how another is expressed, therefore the DNA chromosomes are able to recombine with copies of itself as much as it wants.

3) Distinguish between parental and recombinant phenotypes.

Parental phenotypes are the phenotypes that parents have and the offspring look that way.

Recombinant phenotypes are offspring that have a recombinant phenotype that has an attribute that looks like one of its parents and another attribute that looks like its other parent. This condition could only arise from recombination during Prophase 1 of meiosis.

4) Explain why linked genes do not assort independently. Explain how crossing over can unlink genes.

Linked genes do not assort independently because they depend on each other to be expressed. Crossing over creates new linked gene combinations which allow for variety since now the genes are on separate chromosomes with different traits that they are linked to.

Seite 4

12.4 Q/A

1) Explain how nondisjunction can lead to aneuploidy.

Nondisjunction is when chromosomes fail to separate in anaphase 1 of meiosis, so if a gamete that has suffered from Nondisjunction fertilizes an egg, the resulting zygote will suffer from Aneuploidy, which is when a zygote has an incorrect number of chromosomes for that species.

2) Define trisomy and monosomy. Explain how these major chromosomal changes occur

Trisomy is when there is an additional chromosome.

Monosomy is having only one copy of a chromosome pair instead of the two copies found.

3) Chromosomal mutations are due to chromosomal breakage or unequal crossing over and result in alteration of chromosomal structure. Distinguish among deletions, duplications, inversions, and translocations.

Deletion: when part of a chromosome is lost (from as small as one part of a gene to as large as an entire piece of the chromosome is missing). The offspring that gets this will not have this particular protein or protein(s) which at a minimum will cause a disorder and at most will end up causing the death of the organism.

Duplication: when there is more than one copy of a gene/genes on a chromosome that is caused by the crossing over pieces to both get inserted into the same sister chromatid. The offspring that gets this will have two "doses" of these genes when they should not have.

Inversion: when a piece of a chromosome - moving during recombination in prophase 1 - is attached upside down. In some cases, this can be very bad for the organism that inherits this and in other cases, it is not noticeable.

Translocation: when pieces of non-homologous chromosomes get swapped. This type of mutation can be very bad (death) or cause a mild disorder depending on how large the translocations are.

4) Describe the type of chromosomal alterations responsible for the following human disorders: Down syndrome, Klinefelter syndrome, trisomy X syndrome, Turner syndrome, and chronic myelogenous leukemia.

Duplication - Down Syndrome. Trisomy X syndrome, Klinefelter syndrome

Deletion - Turner Syndrome

Translocation - Chronic myelogenous leukemia

5) Suppose a baby is born with 47 chromosomes, instead of the normal 46: 22 pairs of autosomes, plus two X chromosomes and one Y chromosome. List two different ways that nondisjunction could have resulted in this particular chromosome combination.

The father's sperm didn't split correctly. The mother's egg didn't split correctly.

6) A pregnant woman and her husband are concerned about the possibility their unborn child could have a genetic disorder. They decide to have amniocentesis and karyotyping performed to look for chromosomal abnormalities. It turns out that the child has 47 chromosomes: 23 normal autosomal pairs plus one X chromosome and two Y chromosomes. This chromosomal abnormality resulted from a nondisjunction event during meiosis. Did the nondisjunction occur in the father or in the mother (assuming both have normal karyotypes)? Did the nondisjunction event occur during meiosis I or meiosis II? Explain your reasoning.

In the father during Meiosis 2. Because there is 1 extra chromosome and only human males carry the Y chromosome.