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Chapter 15 Guided Reading Assignment
1. What is the chromosomal basis of inheritance?

Genes have specific loci (positions) on chromosomes, and it is the chromosomes that undergo segregation and independent assortment
-Amy (Blue)


2. What does wild type mean?

The normal phenotype for a character (the phenotype most common in natural populations) such as red eyes
-Amy (Blue)



3. Why was Morgan’s choice of fruit fly such a good one for genetic experiments?

The fruit fly was a great choice for Morgan's genetic experiment because it is a short live organism and is able to breed fast under changing conditions they can complete their life cycle in 10 days and have up to as many as 30 generations a year . This was good because he was able to work under different conditions with those fliesexternal image 43040822708530399.jpgKatie Halbruner



4. How did Morgan associate traits with the sex of the fruit fly?

BE CAREFUL with the way the letters represent the traits – the + superscript means the trait is absent – vg+ means normal wings, not vestigial wings. This is counterintuitive and appears backwards – be careful with it while you read or you will get VERY confused.

Morgan found out that there are some traits in which only males have. He found this out with the white eys of fruit flies. a female count have white eyes in the f2 generation
Katie Halbruner



5. What does it mean when genes are linked or we can say there is linkage?
When there is a linkage in terms of genes it means that there are two genes which are unrelated, but because of their close proximity they stick together during meiosis and eventually when one of the genes is inherited so is the other one.
external image Incomplete-Linakges-in-Linked-Genes-for-Body-colour.jpg

Dahlia M



6. In what step of meiosis, would recombinants form and why?
Recombinants would form during prophase because that is the step during which homologous chromosomes pair up and chromatids cross over, break, and recombine.
external image crossovr.gif

Dahlia M.



7. What is the difference between a genetic map, a linkage map and a cytogenetic map?


A genetic map is an ordered list of the genetic loci along a particular chromosome. A genetic map based on recombination frequencies, specifically called a linkage map. A cytogenetic map located genes with respect to chromosomal features.
map.jpg
cytogenetic map


Taihlor C.




8. Explain the chromosomal basis of sex determination in the following organism:
a. Mammals: The sex of an offspring depends on whether the sperm cell contains an X chromosome or a Y

b. Grasshoppers: females are XX; Males have only one sex chromosome (X0). Sex is determined by whethere sperm cell contains an X chromosome or no sex chromosome.

c. Birds and some fish: The sex chromosome present in the ovum (not the sperm) determines offspring. Females are ZW and males are ZZ.
d. Bees and ants: There are no sex chromosomes. Males are haploid and females are from fertalized diploid.

images.jpg
Taihlor C.





9. What is the SRY gene and why is it important?

The SRY gene is known as the sex determining region of Y. it is located on the y chromosome. it provides instructions for the sex determining region of y protein, meaning it is responsible for the sexual development of males.
Wolffian.jpgpierce_4_10_mid_1.jpg
Ashley A




10. What is a sex-linked gene?

A sex linked gene is a gene located on either sex chromosome (x or y), but x linkages have the most significance.
example:XlinkRecessive.jpg
Ashley A



11. What is X inactivation?





12. Why are most Calico cats female?


13. What is nondisjunction and when in meiosis can it occur?


Nondisjunction- is the failure of chromosome pairs to separate properly during cell division. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes. When a single chromosome is lost (2n-1), it is called a monosomy, in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs. When a chromosome is gained, it is called trisomy, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs.The word nondisjunction means "not coming apart".
-Kelly Sinclair




14. Define the following terms:
a. Aneuploidy- is an abnormal number of chromosomes, and is a type of chromosome abnormality. An extra or missing chromosome is a common cause of genetic disorders (birth defects). Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy occurs during cell division when the chromosomes do not separate properly between the two cells. Chromosome abnormalities occur in 1 of 160 live births, the most common being extra chromosomes 21, 18 and 13.

b. Monosomic-
1. A chromosome having no homologue, especially an unpaired X-chromosome.
2. A single ribosome, especially one combined with a molecule of mRNA.

c. Polyploidy- is a term used to describe cells and organisms containing more than two paired (homologous) sets of chromosomes. Most species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy also occurs in some tissues of animals who are otherwise diploid, such as human muscle tissues

- Kelly Sinclair

15. Explain the following human disorders that result from chromosomal alterations.
a. Down Syndrome- is a genetic condition in which a person has 47 chromosomes instead of the usual 46. In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop. Down syndrome is the most common single cause of human birth defects.
Down-Syndrome-Child-3.jpg

b. Klinefelter Syndrome- is the presence of an extra X chromosome in a male.Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The two sex chromosomes determine if you become a boy or a girl. Females normally have two XX chromosomes. Males normally have an X and a Y chromosome.Klinefelter syndrome is one of a group of sex chromosome problems. It results in males who have at least one extra X chromosome. Usually, this occurs due to one extra X.

c. Turner Syndrome- is a genetic condition in which a female does not have the usual pair of two X chromosomes.Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. Two of these chromosomes, the sex chromosomes, determine if you become a boy or a girl. Females normally have two of the same sex chromosomes, written as XX. Males have an X and a Y chromosome (written as XY).In Turner syndrome, cells are missing all or part of an X chromosome.


d. CML- also known as chronic granulocytic leukemia (CGL), is a cancer of the white blood cells. It is a form of luekemia characterized by the increased and unregulated growth of predominantly myeloid cells in the and the bone marrow accumulation of these cells in the blood. CML is a clonal bone marrow stem cell disorder in which proliferation of mature granulocytes (neutrophils, eosinophils, and basophils) and their precursors is the main finding. It is a type of myeloproliferative disease associated with a characteristic chromosomal translocation called the Philadelphia chromosome.

-Kelly Sinclair



16. What is genomic imprinting?
A genomic imprint is the phenomenon of parent-origin gene expression. The expression of a gene depending upon the parent who actually passed the gene.
external image nrg0101_021a_f3.gif
-Dahlia M.




17. What are extranuclear genes?
- The genes that include DNA present in organelles other than the nucleus occurs in cytoplasmic organelles like mitochondria and chloroplasts
Katie Halbruner external image fig22_09.jpg



18. What are two diseases carried in maternal mitochondria?
Mitochondrial Myopathy, which is weakness, intolerance of exercise and muscle deterioration. Another is Alzheimer’s

Taihlor C.