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MBG 1000 Lecture Notes - Lecture 6: Male Reproductive System, Zygosity, Y Chromosome

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puceporpoise629
6 Apr 2016
School
University of Guelph
Department
Molecular Biology and Genetics
Course
MBG 1000
Professor
Georgevander Merwe

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Document Summary

Monday, february 22, 2016 and wednesday, february 24, 2016 sex linkage. Humans: 2n=46: 22 pairs of autosomes and 1 pair of sex chromosomes. Hemizygocity: when one copy of a gene is present instead of the customary two: there is no counter allele, gene deleted, hemizygous chromosome. When only one copy is present in a diploid organism. Sex-determining region y (sry) gene: encodes the tesis determining factor (tdf) Only found in males: passed from father to son only, found in all male descendants of afected male. Concepts of dominant or recessive does not apply: only one allele (on y) ever present in any one male, y-linked genes are hemizygous. Examples of y-linked disorders: male inferiliiy (1:2000 1:3000 in us, defects in development of male reproducive system. Female-speciic traits and many others: larger coding capacity than y chromosome, all genes on x chromosome deemed x-linked . Paterns of inheritance: male ofspring: x chromosome from mother.

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Related Questions

According to the multiplication rule of probability, the chance of crossing two pea plants that are heterozygous for height and have none of four offspring showing the recessive short phenotype is:A. ¼ × ¼ × ¼ × ¼.

B. ¾ × ¾ × ¾ × ¾.

C. (¼ × ¼ × ¼ × ¼) + (¾ × ¾ × ¾ × ¾).

D. ¼ + ¼ + ¼ + ¼.

E. None of the above.

What characteristic is exhibited by an X-linked trait?

a) Only females have the trait.
b) Females inherit X-linked traits from their maternal parent only.
c) Females can inherit a gene for an X-linked trait from either parent.

d) Males inherit X-linked traits from their paternal parent only.

e) Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.
What characteristic is exhibited by a Y-linked trait?
a) Y-linked traits appear only in male offspring of men with the trait.
b)Y-linked traits are only passed from father to son.
c) Y-linked traits can be passed from mother to son.
d) Both A and B are characteristics of Y-linked traits.
e) Both A and C are characteristics of Y-linked traits.
Which of the following codes for a phenotypic human male?
a) XO with a copy of SRY gene on an autosomal chromosome?
b) XXYY with one copy of the SRY gene deleted?
c) XX with a copy of SRY gene on an autosomal chromosome?
d) All of the above sex compliments results in a person with a sex phenotype of male.
e) XY with the SRY gene located on an autosomal chromosome?
In Drosophila, yellow body is due to an X-linked gene (Xy) that is recessive to the gene for gray body (X+). A homozygous gray female is crossed with a yellow male. What are the genotypes of the F1 progeny?
In some goats, the presence of horns is produced by an autosomal gene that is dominant in males and recessive in females. A horned female is crossed with a hornless male. The F1 offspring are intercrossed to produce the F2. What proportion of the F2 females will have horns?
a)1/2
b)3/4
c)1/4
d) All
None
a) Females are X+X+; males are X+Y.
b)Females are X+X+; males are XyXy.
c)Females are X+X+; males are XyY.
d) Females are X+Xy; males are XyY.
e) Females are X+Xy; males are X+Y.

Females inherit X-linked traits from their maternal parent only.
Females can inherit a gene for an X-linked trait from either parent.
Males inherit X-linked traits from their paternal parent only.
Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.
Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.

11) CIRCLE ALL CORRECT ANSWERS: Human males are hemizygous for

a) Sxl gene b) pseudoautosomal region of the Y c)SRY d) gene for testis determining factor e) Xist gene

12) The X inactivation center codes for

a) gonadal ridges to form ovaries b) gonadal ridges to form testes c) RNA d) testosterone e) protein enhancing transcription of sex linked genes

13) CIRCLE ALL CORRECT ANSWERS: The pseudoautosomal region is found on

a) autosomes in males b) autosomes in females c) X chromosome d) Y chromosome e) both the X and Y chromosome f) could occur in fruit flies

14) Comparing two monozygotic XX twins to two monozygotic XY twins

a) XX are more identical b) XY are more identical c) monozygotic twins do not occur

EXPLAIN YOUR ANSWER:

15) CIRCLE ALL CORRECT ANSWERS: Butterflies and Habrobracon differ in

a) which sex is homogametic b) which sex is monoploid c) one has sex chromosomes and the other does not d) one produces some gametes by mitosis, the other does not

___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 organism’s 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).