The gingham dog and the calico cat
Side by side on the table sat;
'T was half-past twelve and (what do you think!)
Nor one nor t'other had slept a wink!
The old Dutch clock and the Chinese plate
Appeared to know as sure as fate
There was going to be a terrible spat.
(I wasn't there; I simply state
What was told to me by the Chinese plate!)

The gingham dog went "bow-wow-wow!"
And the calico cat replied "mee-ow!"
The air was littered, an hour or so,
With bits of gingham and calico,
While the old Dutch clock in the chimney-place
Up with its hands before its face
For it always dreaded a family row!
(Now mind: I'm only telling you
What the old Dutch clock declares is true!)

The Chinese plate looked very blue,
And wailed, "Oh, dear! What shall we do!"
But the gingham dog and the calico cat
Wallowed this way and tumbled that,
Employing every tooth and claw
In the awfullest way you ever saw-
And, oh! How the gingham and calico flew!
(Don't fancy I exaggerate-
I got my news from the Chinese plate!)

Next morning, where the two had sat
They found no trace of dog or cat;
And some folks think unto this day
That burglars stole that pair away!
But the truth about the cat and pup
Is this: They ate each other up!
Now what do you really think of that!
(The old Dutch clock it told me so,
And that is how I came to know.)

The Duel
by Eugene Field (1850-1895)

(Poems of Childhood)

Chromosomes

Assignment

Audesirk, Audesirk & Byers part of Chapter 12, and several other figures

Today's musical selection
Beatles Ob la di
A cover of this song was the theme for the TV situation comedy Life goes on where Corky has Down syndrome

Of course, genes come on chromosomes.
There are autosomes and sex chromosomes.

Sex linkage

Figure 12-21
XY

Figure 12-22
sex determination

Figure (Chapter 10 opener)
Case study - Vive la difference Chapter 10, p. 167
Case study revisited Chapter 10, p. 186
Different organisms have different chromosomal means of sex determination (dimorphism).
Sry gene on Y codes for TDF (testicular determining factor)
In female, Wolffian ducts degenerate and Mullerian ducts develop into oviducts, uterus, and cervix (default pathway).
In male, testes make testosterone and MIH (Mullerian inhibiting factor), Mullerian ducts degenerate, Wolffian ducts become epididymus, vas deferens and seminal vesicles (active, not default)
urogenital groove becomes external genitals

Cartoon
In humans, Y determines male-ness and there are virtually no genes on Y except to differentiate testes in male.
Why map the Y? Science 261, 1993, p. 679
A guy bashing joke with genes like "inability to say 'I love you'" over the phone called "ME-2"
However, I am showing this picture to also make a serious point -- genes eventually get assigned to locations on the chromosome, but first, genetic linkage must be established
Linkage:
Independent assortment (Mendel's 2nd law) does not apply to genes (near enough to each other) on the same chromosome.
map location is based on cross-over probability (determined with a genetic cross)

Figure 12-23
Sex linked inheritance in Drosophila, white x red eye cross. Note that there is no corresponding gene on the Y, hence the term hemizygous.
males are XY, but tissues that are XO are male (though if fly or germ cells are X0, fly is sterile) and XX tissues are female, thus sex is based on number of X chromosomes. grasshopper XO male

Figure 10-13
X inactivation in calico cat

Figure 10-12
XX Barr body, X inactivation Mary Lyon
dosage compensation

Chromosomal abnormalities

Figure 12-32
Chromosomal Abnormalities
Nondisjunction e.g. trisomy
lethal, spontaneous abortions

Table 12-2
X abnormalities survive
Klinefelter's XXY
Supermale XYY
1968 prison if taller than 71 inches 1/11 XXY or XYY
population XXY - .08-.092%
XYY - .069-.095%
Research to find if people have X or Y abnormalities is controversial, for instance because of self-fulfiling prophesy.
It was widely rumored that Richard Speck, known for his mass murder of 8 student nurses in Chicago in 1966, was XYY.
Turner X0 1/2000 females
spatial sense abnormal

Figure 12-33
Autosomal aneuploidies are often lethal
Trisomy 21 = Down's syndrome
(the term "Mongulism" is used less in this era of political correctness, especially in light of Down's unsavory attitude toward non-European races in his writings)
retarded but nice, increases with increasing maternal age and is in percents for women over 40
age 40 almost 1% age 50 almost 10%

Figure 12-34
Here is a graph of that increase with age

Figure E13-5
Many couples choose to test the chromosomes of the fetus using amniocentesis of chorionic villus sampling

All human "eggs" are already made around the time of birth (while sperm are made throughout life). It seems likely that either "eggs" suffer from aging (alternatively the good ones are used in the earlier reproductive years).

Questions used in 2007 & 2008 related to this outline

What would have happened if Mendel had done his dihybrid cross using two traits that were near each other on the same chromosome?
(a) That is what he did and how he got the 3/1 ratio.
(b) That is what he did and how he got the 9/3/3/1 ratio.
*(c) His ratio would not have been 9/3/3/1 and he might have discovered linkage.
(d) That is what he did and how he obtained the ratio of ABO blood groups.
(e) He would have discovered Klinefelter syndrome.

Why is there a relatively high frequency of X chromosomal aneuploidies?
(a) The X chromosome is not subject to amniocentesis.
(b) The X chromosome is even smaller than chromosome 21.
(c) There are many nondisjunctions when mitosis involves the X chromosome.
*(d) All but one X chromosome is inactivated.
(e) X chromosomal abnormalities are not detected in chorionic villus sampling.

The human Y chromosome
(a) has most of the genes that are on the X.
*(b) is important for sex determination.
(c) is not as important for sex determination as the number of X chromosomes.
(d) is seen histologically as the Barr body
(e) is the cause of coat color mosaicism in the Siamese cat

A female fruit fly homozygous for red eyes is mated to a white eyed male.
*(a) Male and female offspring are red eyed.
(b) Female offspring have red eyes but males have white eyes.
(c) Female offspring have white eyes but males have red eyes.
(d) Female and male offspring have white eyes.
(e) Female and male offspring have pink eyes, halfway between red and white.

Amniotic fluid
(a) is used for chorionic villus sampling.
*(b) should contain no maternal cells.
(c) is used for cloning.
(d) is the source of prions.
(e) would be present only if nondisjunction had occurred during mitosis.

Which is a way to test for chromosomal abnormalities in the embryo?
(a) gel electrophoresis
(b) administering dopamine
(c) using rubella
(d) testing for chorionic gonadotroin
*(e) chorionic villus sampling

Children with Down syndrome
(a) are heterozygous.
*(b) have 47 chromosomes.
(c) accumulate glycolipids from an enzymatic deficiency.
(d) have a mutation of a gene on chromosome 21.
(e) are born when older men decide to have children.

Name a cell that could have 22 autosomes and one Y chromosome.
(a) a human egg
*(b) a human sperm
(c) a human diploid cell
(d) a body cell from a Klinefelter's syndrome individual
(e) a cell from a Turner's syndrome individual

A human female has one X chromosome with the normal gene and the other with the recessive mutated gene.
(a) She passes the normal gene to her daughters and the mutated gene to her sons.
(b) She is called "hemizygous."
(c) All her daughters are carriers since she passes both X chromosomes to daughters.
*(d) She is a mosaic of cells expressing one or the other X.
(e) Her sons would have Klinefelter's syndrome

The testicular determining factor is found in what chromosome in humans?
(a) X
(b) #21
*(c) Y
(d) No single chromosome; it is explained by polygenic inheritance.
(e) The chromosome has not been identified yet.

"Early female sexual development is the default." Meaning?
(a) Like with fruit flies, two X chromosomes specify female development.
*(b) Ducts become female genitals in the absence of factors present in the male.
(c) Many genes specifying male characteristics are mapped to the Y chromosome.
(d) Since females have two X chromosomes and males have one, it is no wonder males and females are different.
(e) That is the statement that got Lawrence Summers fired as president of Harvard.

'Dosage compensation explains the high prevalence of abnormalities like Turner's syndrome and Klinefelter's syndrome.' Dosage of
*A) genes on the X chromosome
B) p53
C) colchicine
D) polar bodies
E) antibodies

Chromosome map position
A) was first determined in Darwin's classic genetic experiments.
*B) is based on the cross-over frequency for linked genes.
C) is determined by the normal distribution.
D) was 9:3:3:1 when Mendel figured it out.
E) is calculated using the Punnett square.

Amniotic fluid
A) causes mutations.
B) is hybrid in the F1 generation.
C) is the universal donor in blood transfusions.
D) is produced by the Sry gene on the Y chromosome.
*E) can be used to screen for chromosomal and genetic abnormalities in the fetus.

The failure of chromosomes to distribute equally to gametes is called
*A) nondisjunction.
B) conjugation.
C) segregation.
D) inversion.
E) independent assortment.

Which disorder is more common among the babies of older mothers?
A) Turner syndrome
B) XYY
C) hemophelia
D) Huntington's disease
*E) Down syndrome

Klinefelter syndrome
A) results when detrimental alleles become homozygous because of incest.
B) is an autosominal dominant disorder.
C) females would lack a Barr body.
*D) results from sex chromosomal nondisjunction.
E) is because of crossing-over.



Questions used in 2002 relating to this outline (and other outlines) [some overlap particularly with genetics questions]

In your genetics coverage, you were introduced to the term "locus." Of the following, which would be the best term to substitute for "locus?"
(a) true-breeding
(b) hybrid
(c) chromosome
*(d) gene
(e) allele

Most people have two copies of chromosome 21. These two copies would be called
(a) alleles.
(b) tetrads.
*(c) homologues.
(d) spindles.
(e) centromeres.

Name a cell that could have 22 autosomes and one Y chromosome.
*(a) a human sperm cell
(b) a human ovum
(c) a human diploid cell
(d) a body cell from a Klinefelter's syndrome individual
(e) a cell from a Turner's syndrome individual

Which is a dominant lethal mutation which probably would not be expressed until after affected men and women have had children?
(a) Down's syndrome
(b) PKU
*(c) Huntington's chorea
(d) Tay Sachs disease
(e) Sickle cell anemia

Which is a mutation?
(a) Klinefelter's syndrome
*(b) Tay Sach's disease.
(c) Down's syndrome
(d) XYY
(e) Turner's syndrome

A person has 44 autosomes plus one X chromosome plus one Y chromosome. Which statement is true for this person?
*(a) The Y chromosome came from the father.
(b) The X chromosome becomes a Barr body.
(c) The X chromosome could have come from either the father or the mother.
(d) The Y chromosome's inactivation is described by the Mary Lyon hypothesis.
(e) This person has Klinefelter's syndrome.

Which statement applies to the Siamese cat having white fur with black extremities?
*(a) A mutation makes an enzyme for melanin synthesis temperature-sensitive.
(b) Black vs. white depends on which X chromosome is active.
(c) There is incomplete dominance like for snapdragon flower color.
(d) The cat is heterozygous for the body color gene.
(e) Sons of such a female cat will be either black or white.

To see whether your baby would be born with trisomy-21, you could use
(a) recombinant DNA.
(b) a microarray.
*(c) chorionic villus sampling.
(d) autoradiography.
(e) reverse transcriptase.

Which is the best statement about human chromosomes?
(a) Presence of two X chromosomes causes development of the female.
*(b) Dosage compensation in females works by X chromosome inactivation.
(c) Male development begins under the control of the one X chromosome.
(d) The male genome is haploid while the female genome is diploid.
(e) The Y chromosome has all the same loci as the X chromosome.

This page was last updated 7/13/09

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