BSC 1010 Lecture Notes - Peter H. Raven, Dna Ligase, Helicase

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17 Jul 2013

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A) explain what is sex linkage, and b) apply the concept of sex linkage to explain why color blindness is more prevalent in men than in women. A sex linkage is when a gene is located on one of the sex chromosomes instead of the other chromosomes. This is caused by recessive mutant alleles on the x chromosome. The y chromosome contains fewer functional alleles than the x chromosome and it does not include those involved in this disease. In every cell, only 1 of the set of 2 chromosomes is used, which is switched off at a random process and is independent in every cell. In females this principle applies to the x chromosomes, as both are fully functional. If the mutant allele is present on one of the x chromosomes, it is expressed in 50% of cells; however, it is still preformed because the other 50% of cells easily compensate for the mutant allele.

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Complete the following paragraph to learn about x-linked inheritance. expressed, men, sex-linked, ... Question: Complete the following paragraph to learn about X-linked inheritance. expressed, men, sex-linked,... Complete the following paragraph to learn about X-linked inheritance. expressed, men, sex-linked, repressed, X, Y, autosomal, two, one Sex-linked alleles have a different pattern of inheritance compared to those found on ____________ chromosomes. This is because on ____________ alleles, the allele is only carried on the X chromosome and not the Y chromosome. That means that females can pass down diseased alleles to offspring through ____________ ____________ chromosomes, while males can pass down alleles through ____________ ____________ chromosome. For this reason, it is more likely that ____________ are afflicted with sex-linked diseases, because whatever allele is carried on their ____________ ____________ chromosome is ____________ .

___1. Nationally, the most common cause of Down Syndrome is
a. nondisjunction of Chromosome 21 during meiosis
b. translocation of Chromosome 21 onto another chromosome
c. inversion of a large section of Chromosome 21
d. deletion of the Down Syndrome gene
___2. In humans, sex is determined by
a. The presence or absence of the Y chromosome
b. The ratio of X chromosomes to sets of autosomes
c. The temperature during fetal development
d. Which parent is stronger at the time of conception
___3. A translocation is
a. a chromosomal abnormality in which a piece of one chromosome breaks off and attaches to a different chromosome
b. an abnormality in which the chromosomes are translocated out of the nucleus
c. a condition in which the chromosome has broken in two places and come back together with the middle segment backward
d. an abnormality in which there is an extra copy of one chromosome
___ 4. In snapdragons, a red-flowered plant crossed with a white-flowered plant produces all pink-flowered offspring. But crossing two pink-flowered plants produces red, pink, and white in a 1:2:1 ratio. This is a good example of
a. Incomplete dominance
b. Dominance of the red allele over the white allele
c. Lethal effects of the pink allele
d. Sex-linkage of the flower-color alleles
___ 5. If a person with type AB blood marries a person with Type O blood, what blood types are possible in their children? (Assume this trait is a single-gene trait, not complicated by interaction with other genes).
a. A, B, AB, or O
b. A or B only
c. AB or O only
d. AB only 2
___6. In what phase of meiosis are haploid nuclei first formed? a. Anaphase I b. Metaphase II c. Telophase II d. Metaphase I e. Telophase I
___7. What is the phenotype of a heterozygous tall pea plant? a. tall b. Tt c. TT d. tt e. dominant
___ 8. If genes A and B are far apart on a chromosome, and A and C are close together, which of the following observations is expected?
a. Crossing over will occur more often between A and C than between A and B
b. Crossing over will occur at equal frequencies between A and C, and between A and B
c. Crossing over will occur more often between A and B than between A and C
___9. Sometimes an organismâs genotype for one gene masks the effect of a different gene. This phenomenon is called
a. Dominance
b. Incomplete dominance
c. Co-dominance
d. Epistasis
e. Variable expressivity
___10. The dominant allele of a gene is
a. The one that is expressed most often in a population
b. The one that is expressed most often in any particular cross
c. The one that is expressed in an individual that has two different alleles
d. The one that is most healthy to have, that gives the greatest fitness
___11. In human cells, DNA replication occurs
a. In S phase of interphase
b. In G1 phase of interphase
c. In G2 phase of interphase
d. In prophase of mitosis
e. Whenever the cell needs to read the DNA to make proteins
___ 12. A process in which recipient cells take up genes from DNA molecules floating free in the surrounding medium is called
a. conjugation
b. specialized transduction
c. generalized transduction
d. transformation 3
___ 13. Most calico cats are female. However, a few rare males are observed. What is the genotype of a male calico cat?
a. X BX 0
b. X OY
c. X BY
d. X BYY
e. X BX OY
___ 14. A type of red-green color-blindness is a sex-linked (X-linked) recessive trait in humans. Can a woman have this type of color-blindness?
a. Yes, a woman could be color-blind if her mother and father were both heterozygous.
b. Yes, a woman could be color-blind but only if she has an abnormal number of sex chromosomes.
c. No, women can't show sex-linked traits because they lack a Y chromosome.
d. No, women can't show sex-linked traits because they have two X chromosomes.
e. Yes, a woman could be color-blind if her father was color-blind and her mother was a carrier (heterozygous).

Please explain, and no hand-written work please, please type answer

Sex-Linked Traits (traits located on the sex chromosomesâusually the X chromosome)

Follow the directions for the lab. Enter data you obtain for the following crosses and answer questions on this answer sheet. (NOTE: The traits used in this Module 3 Lab are sex-linked. Therefore, you CANNOT click the âignore sexâ button for these crosses. You need to see separate results for males and females to analyze data for sex-linked traits.)

Question: In this lab exercise, should you click the "ignore sex" button for the crosses?

1. a. Perform a monohybrid cross between a female fly with a tan body and a wild-type male fly. Show results for the F₁ offspring. (NOTE: You will use these F₁ flies in the next cross.)
ENTER DATA HERE:

Question: Are the phenotypes of the F₁ offspring what you would have predicted for this cross: why or why not?

Question: Each F₁ female received a tan allele from her mother and a wild allele from her father. Why do all of the F₁ females show the wild-type phenotype?

Question: Compare the number and type (X or Y) of sex chromosomes found in female and male flies.

Question: Compare the number of alleles present on the X and Y chromosomes.

Question: How can you tell that tan body is a sex-linked trait?

Question: How can you tell whether tan body is located on the X chromosome or the Y chromosome?

Question: If tan body was located on the Y-chromosome, what would be the phenotype of all the male F₁ offspring? Is this what you obtained for the cross above?

Question: If tan body was located on the Y-chromosome, could females even show the trait? (HINT: When analyzing the cross results, remember that Y-linked traits are passed down only from affected males to their sons. Females cannot display Y-linked traits since they do not have Y chromosomes. On the other hand, both males and females can inherit X-linked traits since they both have X chromosomes.)

PUNNETT SQUARE:

List the genotypes of the parent flies in this cross (HINT: You must use X and Y symbols):

List the gametes produced by each parent fly in this cross:

Show the Punnett Square for the above cross.

BSC 1010 Lecture Notes - Peter H. Raven, Dna Ligase, Helicase

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