BIOL 151 Lecture Notes - Lecture 17: Thomas Hunt Morgan, Y Chromosome, Meiosis

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17 Apr 2017

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In many animals, sex is genetically determined and associated with chromosomal differences: the sex of an individual is determined by a special pair of unmatched chromosomes known as sex chromosomes. X chromosome and a y chromosome: the relative size and gene content of the x and y chromosomes differ greatly among species. This is the primary sex ratio, and it is not easily observed because the earliest stages of fertilization and development are inaccessible to large- scale study. The secondary sex ratio can be observed at birth, and it differs among populations but usually shows a slight excess of males. 17. 2 inheritance of genes in the x chromosome. Genes in the x chromosome are called x-linked genes. He realized that, when crossing the flies, that only the males could get the white-eyed gene. Genes in the x chromosomes exhibit a crisscross inheritance pattern. Biol 151 chapter 17: the key features of x-linked inheritance happen because:

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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.

___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).

1. If you had a fruitfly with phenotype A, what test would you make to determine if it was Aa or AA? Explain the different outcomes expected if the fly in question is AA or Aa.

2.The sex of birds, some insects, and other organisms is determined by a ZW chromosomal arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to XY in humans). Assume that a recessive lethal allele on the Z chromosome causes death of an embryo in birds. What sex ratio would result in the offspring if a cross were made between a male heterozygous for the lethal allele and a normal female?

3.A recessive gene for red-green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color-blind) marries a color-blind male. What is the likelihood that this couple's first son will be color-blind?

4. One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that they will have a daughter with hemophilia? (Note: In this problem, you must include the probability of having a daughter in your computation of the final probability.)

5. One form of hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a phenotypically normal woman whose father had hemophilia. What is the probability that their first son will have hemophilia?

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BIOL 151 Lecture Notes - Lecture 17: Thomas Hunt Morgan, Y Chromosome, Meiosis

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