9) Why is a photograph of cells in metaphase utilized when constructing a karyotype? (5 points)
The most easily identified stage of cell division is the metaphase where the chromosomes align at the equator of the cell. Thus, at metaphase, the chromosomes are compact and clearly visible and can help in preparing a karyotype.
10.What does it mean to be a carrier of a genetic defective characteristic? When might it be important to know if one is a carrier? (5 points)
A carrier is a person who does not have the disorder itself but has a defective recessive allele for the disorder.
This recessive allele when paired with another recessive will express the disorder.
It is important to determine carriers when a genetically inheritable disorder runs in a family.
Two unaffected people who each carry one copy of the mutated gene for an autosomal recessive disorder (carriers) have a 25 percent chance with each pregnancy of having a child affected by the disorder. The chance with each pregnancy of having an unaffected child who is a carrier of the disorder is 50 percent, and the chance that a child will not have the disorder and will not be a carrier is 25 percent
- From the hemophilia procedure with a population of 120 individuals (n = 120): (4 points) A. What were the possible genotypes of the offspring? B. What is the probability of males having hemophilia out of the entire population? C. How many females would have hemophilia? D. How many carriers would there be?
Father is hemophilic and mother is carrier.
Parents XY XX
Phenotype haemophilic Carrier
Genotype XhY XHXh
Alleles Xh and Y XH and Xh
Genotypes of the offspring
1/4th of the males will be haemophilic i.e. 30
1/4th of the females will be hemophilc.i.e. 30
1/4th of the females will be carriers.There will no males as carriers because males have only one X chromosome and in hemophilics the X chromosome with recessive allele expresses the disorder.
- Explain why more males tend to suffer from X-linked disorders than females. (5 points)
Most sex-linked disorders are carried on the X chromosome. Since males only have one X chromosome, recessive disorders carried on the X chromosome are much more common in males. This is because in females, a normal gene on their other X chromosome would stop the recessive disorder from being expressed.
13.The student has a friend that knows the student is taking Biology, and she is confused about her blood type. Her blood type is O, but her dad is A and her mother is B. She asks the student if it is possible for her parents to have a child that is O. Explain the answer to her. (5 points)
The parents are heterozygous for their blood groups. The father has alleles A and O and the mother has alleles B and O.
Genotype XY XX
Blood group OA OB
Inheritance XX XY
OO (O group daughter) AB
- In a flower garden, the student has purple and white pansies. The student notices that a new pansy has sprouted. When it finally flowers, the pansy is lavender. Explain how this happened. (5 points)
A cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits.
Denoting purple pansy as PP white pansy as pp lavender as Pp
Phenotype Purple white
Genotype PP pp
F1 generation Pp lavender Pp
The dominant allele P for purple colour is not completely expressed over the recessive allele p for white colour. Hence, the offspring produced is lavender.
15.With a botanist friend’s help, the student decide to cross the lavender pansy with the white pansy. Will this result in any purple pansies? Explain. (5 points)
Yes it will. This cross is called a test cross.
Phenotype lavender lavender
Genotype Pp Pp
Alleles P and p
1 out of 4 flowers will be purple.