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light brown or lighter. Were the dark brown parents truly homozygous in hair color, and did the hair color of the offspring not grow darker with age, Mendelian expectation would be 100 per cent. dark brown. Actually, the result falls far short of that, just as the necessary conditions are far from being met. It is highly probable that in some of these families (notably Gil-B, Gue and Huf, and probably also Lat-A and Wil-D) the darker parent actually forms germ cells that lack black pigment. Of the four lightest haired children the ages of three that are known are 8, 10 and 15 years-ages at which the adult color is not fully shown. Under these circumone can not predict with certainty the outcome of matings of this class. One can only say that the proportions of light brown children and those with lighter hair should be less in proportion to the darker haired children in class B than in class A. The actual proportions in the two classes are in the direction of this expectation.

stances

TABLE V.

DISTRIBUTION OF HAIR COLOR IN THE OFFSPRING WHEN ONE PARENT HAS BLACK HAIR AND THE OTHER LIGHT BROWN HAIR (NO DIVISION, ON ACCOUNT OF FEWNESS OF FAMILIES)

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Assuming what is probably true for all the families, that the black-haired parent produces an equal number of germ cells with a tendency toward lighter hair and toward black, we should expect an approach toward an equality

FM.

FF.

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of light and dark haired offspring. Actually, the lighter colors are in excess-a result again doubtless due to the

TABLE VI.

DISTRIBUTION OF HAIR COLOR IN THE OFFSPRING WHEN ONE PARENT HAS BLACK HAIR AND THE OTHER BROWN HAIR

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relative immaturity of the children as compared with their parents.

Assuming, as in the discussion of Table V, that the blacks are heterozygous (except in the Ste-D family) we should expect an equality of dark and light haired offspring modified by preponderance of the lighter type owing to the immaturity of the average of the offspring. Actually, with brown hair and lighter there are 41 children as opposed to 7 (Ste-D omitted) kith either black or dark brown hair. When we compare the proportion of the children having hair brown or darker in this Table (60 per cent.), with that in Table V (36 per cent.) we realize how much more frequent the darker classes have become with the increased darkness in the hair of the second parent.

On account of the impossibility of drawing the line between the dark and the light shades of hair and on account

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Reference
Letters.

of the light color of immature offspring we are able only to compare this section with that which follows.

TABLE VII. DISTRIBUTION OF HAIR COLOR IN THE OFFSPRING WHEN BOTH PARENTS HAVE DARK BROWN OR BLACK HAIR

(a) When Both Parents Probably Form Light Germ Cells and Dark in

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Cla-A

Cur

Fue

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Gla-B

1 1

Gor-A

2 3

2

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2

2 1

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dk.br. N.

N.

br.

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br.

Had

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Har-A

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Hem-A

1 1

Mck

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lt.br. dk.br.

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Assuming that the qualities of light hair color and dark hair color (or absence and presence of intensifier) segregate in parents of mixed origin expectation is that Series A would yield 75 per cent. dark haired offspring, but on account of the impossibility of drawing the line between the dark and light shades of hair and on account of the light color of immature offspring we are able only to compare this series with series b in which expectation is 100 per cent. offspring of the darker color. Actually, in series there are 59 individuals light to 137 (or about 70 per cent.) dark while in series a only 55 per cent. are

dark.

A part of these light haired individuals probably result from recessive light hair color of parents and a part from immaturity.

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(b) When Both Parents are not Known to Form Light Germ Cells

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FF.

Reference Letters.

C. HEREDITY OF RED AND BROWN PIGMENT We have seen that the red series is quite independent of the yellow-brown series. Clear red-haired individuals lack black pigment themselves and can not transmit it to their offspring. This is, at least, a priori probable; but despite careful search we have found no case of two parents with clear red hair. One case of clear red and dark réd is given in Table I., Edw family, in which all three children have red hair. × dark red parentage with record (as yet unchecked).

OFFSPRING.

We have one of dark red

the following remarkable

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Dey-B

1 3 1 4 dk. red dk. red.

N

br.

N

We interpret this case to mean that the red is absent in some children (owing to heterozygotism of the parents) and dilute in others and here masked by black pigment.

TABLE VIII. DISTRIBUTION OF HAIR COLOR IN THE OFFSPRING WHEN ONE PARENT HAS HAIR OF A CLEAR RED COLOR; THE OTHER OF A BROWN

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In this table the yellow-brown series of colors predomi

nates

among the offspring over the reds.

This we inter

pret to mean that, as the red parents are usually heterozygous in the intensity of red that they bear, we have approximately one half of the offspring without any (or

only

a slight) tendency toward red.

Even when red

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