PartLIII: The Eugenics Movement; Bad Science

The major focus of Essay LIII is the historical development of pedigree charts, their purpose, and how they have been used by misguided individuals to promote racial injustice.  Simple genealogical charts have been around for centuries. Bacteria, fungi and other living organisms
with short life cycles serve as excellent subjects for genetic studies for obvious reasons. Humans, on the other hand, make poor subjects simply because no one lives long enough to observe several generations.  Furthermore,  a major tool of genetics is based on a controlled experiment which is highly unlikely since it means requiring (forcing?) two “purebred” individuals (for certain traits)to mate to study a given trait Consequently, geneticists have relied on case studies, twin studies, and pedigree charts.

Pedigree charts are a series of horizontal  lines which connect mates and siblings and vertical lines that connect generations. Circles represent females and squares represent males (and yes, I used to tell the boys in my classes that “they’re telling use we’re square!)” Affected-individuals for the trait (condition) are usually shaded in; carriers (heterozygotes) are usually half shaded squares or circles and dominant homozygotes (unaffected) individuals) are colorless. Pedigrees can now be used for testing as specific as single nucleotide differences in genes. Below, please find two pedigrees for hemophilia in the Royal family of England.

Pedigrees play a very important role in medical genetics and genetic counseling but what most people don’t know (including me until recently) is that pedigree analysis had a dark beginning in that it was developed by eugenicists who used the principles of genetics (a true science) to further  the pseudoscience of eugenics and apply it  to a social movement with the goal of controlling human heredity. The name most associated with eugenics is Charles B. Davenport, who tried to apply Mendelian genetics to social conditions such as alcoholism, criminality  and feeble- mindedness. In other  words, eugenicists used pedigrees to  try to explain a genetic link to mental, emotional, and behavioral characteristics. Their claims lacked scientific scrutiny, (hypothesis generation, empirical data collection, observation, peer review, etc.).    Davenport first introduced pedigrees in 1911 when his book Heredity in Relation to Eugenics was published and when the field of genetics was in its infancy and long before the chemical and physical basis of the gene and especially the DNA molecule were elucidated.  In fact, only a few years before Friedrich Miescher, a German physician had isolated a little-known chemical in the cell’s nucleus that was sugary, was slightly acidic, and contained phosphorous. Robert Feulgen, another German in 1914 found that it stained red when a dye, fuchsin, was applied and before the long debate among biologists and biochemists of which molecule, protein or DNA contained the hereditary code.
And what a fascinating story that was! See essay XX. (Baumer, L.)

When examining a pedigree to determine the specifics of a given trait or condition, the first thing to do is to determine the mode of transmission.   In other words, is the trait autosomal dominate (autosomal meaning the gene(s) is (are)) found on chromosome l-22, autosomal recessive (two non-dominant alleles (i.e., rr or hh)) and found on chromosome 1-22, X– linked dominant (like autosomal dominate meaning only one allele for the trait is required for the trait but unlike autosomal, the allele is found on a sex chromosome (X or Y)), or  X- linked recessive, needing only one allele for the trait to show up.  Perhaps you are wondering why I said  only one recessive allele is necessary for the trait to show up?  This is  because in sex (X) linked traits, the Y chromosome is very small and is devoid of many genes (alleles) that are only found on the X chromosome.

When completing this pedigree with autosomal recessive inheritance, individuals that are shaded are expressing the recessive phenotype and have a genotype of, say, “rr”. Use this knowledge and additional knowledge about how genes are passed from generation to generation to complete the remainder of the pedigree.

  It is possible to work backwards to determine the genotypes of the parents if the phenotype of a child is known in an autosomal recessive trait.  For example, if the child has the condition in unknown autosomal recessive traits, the parents must be heterozygous carriers but don’t have the condition.  A skipped generation, is often a clue of an autosomal recessive trait.

Examples: Cystic fibrosis, Sickle cell anemia,Tay-Sachs disease

Patterns for Autosomal Recessive Inheritance

After filling in the genotypes for individuals in several family trees that exhibit this mode of inheritance, some patterns that can be noticed are:

• Males and females have the same chance of expressing the trait
• You can only express the trait if you are homozygous
• If both parents express the trait, then all their offspring should also express the trait
• If the offspring express the trait but their parents don’t, then both parents are heterozygous
• If one parent expresses the trait, then their offspring who don’t express it are heterozygous
• The trait can skip generations

On the other hand, an autosomal dominate trait in an offspring cannot come from two  unaffected parents.  Skipped generations are not a sign of an autosomal dominant trait.

When completing this pedigree with autosomal dominant inheritance, individuals that are non-shaded are expressing the recessive phenotype and have a genotype of “rr”. Use this knowledge and additional knowledge about how genes are passed from generation to generation to complete the remainder of the pedigree. Shaded individuals will either have a genotype of “Rr” or “RR”. .

Examples: familial hypercholesterolemia,  hypertrophic cardiomyopathy (HCM), Marfan’s syndrome (MFS)

Patterns for Autosomal Dominant Inheritance

After filling in the genotypes for individuals in several family trees that exhibit this mode of inheritance, some patterns that can be noticed are:

• Males and females are equally likely to have the trait.
• There is male to male transmission.
• Traits do not skip generations (generally). If the trait is displayed in offspring, at least one parent must show the trait.
• If parents don’t have the trait, their children should not have the trait (except for situations of gene amplification).
• The trait is present whenever the corresponding gene is present (generally). If both parents possess the trait, but it is absent in any of their offspring, then the parents are both heterozygous (“carriers”) of the recessive allele.
• Homozygotes for the dominant condition have a more severe form of the condition.

Remember:

• Genes act in pairs, one from each parent.
• Gene pairs separate during meiosis and the formation of the sex cells along with the chromosomes.
• When the sperm fertilizes the egg, the father’s genes (and chromosomes) join the mother’s, or both contribute to the genetic makeup of the offspring.
• One form of a gene may be dominant over another form which is recessive and the dominant form would be expressed. (MI Genetics Resource Center)

The next step is to determine if the trait is autosomal or X-linked.   If the condition favors one sex (i.e. males) more than the other sex, it is sex-linked and if females don’t have the-condition (i.e. genotype X^RX^R or X^R X^r), and only males have the trait,(X^rY), it is an X- linked recessive trait. (Shotwell, M)

When completing this pedigree with X-linked recessive inheritance, use the symbols X and Y in the genotype to represent the sex chromosomes passed on from the previous generation. The X chromosome will contain the alleles for the trait and the Y chromosome will have no alleles for this trait. When completing this pedigree with X-linked recessive inheritance, shaded females who are expressing the recessive phenotype can only have the genotype of X^rX^r, the shaded males who are expressing the recessive phenotype can only have the genotype of X^rY, and the non-shaded males who are expressing the dominant phenotype and can only have the genotype X^RY. U

Examples: red-green color blindness and hemophilia A

Patterns for X-linked Recessive Inheritance

After filling in the genotypes for individuals in several family trees that exhibit this mode of inheritance, some patterns that can be noticed are:

• The trait is more common in males than in females.
• If a mother has the trait, all of her sons should also have it.
• There is no male to male transmission.
• It has the same inheritance patterns as autosomal recessive for human females.
• The son of a female carrier has a 50 percent chance of having the trait.
• Mothers of males who have the trait are either heterozygous carriers or homozygous and express the trait.

Real Examples: Hemophilia, Muscular Dystrophy and Fragile X.

Remember:

• The father passes his X sex chromosome (and all its genes) to his daughters and his Y sex chromosome (with its genes) to his sons.
• Genes act in pairs, one from each parent for the females. For this mode of inheritance, males get their gene for the trait from their mother.
• Gene pairs separate during meiosis and the formation of the sex cells along with the chromosomes.
• When the sperm fertilizes the egg, the father’s genes (and chromosomes) join the mother’s, or both contribute to the genetic makeup of the offspring.
• One form of a gene may be dominant over another form which is recessive and the dominant form would be expressed.

When completing this pedigree with X-linked dominant inheritance, non-shaded females who are expressing the recessive phenotype can only have the genotype of X^rX^r, the non-shaded males who are expressing the recessive phenotype and can only have the genotype of X^rY, and the shaded males who are expressing the dominant phenotype and can only have the genotype .X^RY.

Examples:Renal phosphate transport disorder, Vitamin D Deficiency, Rickets

Patterns for X-linked Dominant Inheritance

After filling in the genotypes for individuals in several family trees that exhibit this mode of inheritance, some patterns that can be noticed are:

• All daughters of a male who has the trait will also have the trait.
• There is no male to male transmission; the trait follows the inheritance of the X-chromosome.
• Sons can have the trait only if their mother also has the trait.
• Same inheritance pattern as autosomal dominant traits in human females.

Remember:

• The father passes his X sex chromosome (and all its genes) to his daughters and his Y sex chromosome (with its genes) to his sons.
• Genes act in pairs, one from each parent for the females. For this mode of inheritance, males get their gene for the trait from their mother.
• Gene pairs separate during meiosis and the formation of the sex cells along with the chromosomes.
• When the sperm fertilizes the egg, the father’s genes (and chromosomes) join the mother’s, or both contribute to the genetic makeup of the offspring.
• One form of a gene may be dominant over another form which is recessive and the dominant form would be expressed.

Returning to the dark side of the eugenics movement, the dihybrid cross was employed to support claims of genetic differences between races and a rationale for prohibiting interracial marriages. Eugenics misguided thinking probably reached its most radical extreme in Nazi Germany with Adolf Hitler’s experiments to produce a “super” race which takes us back to the beginning arguments for people not being good subjects in genetic matings. The eugenics movement can be traced back to Francis Galton who just happened to be  Darwin’s half cousin. We will finish the eugenics movement in the next essay.

 

References

Baumer, L. Republish date Aug. 12, 2020 Part XX: DNA or Protein; The Great Debate Bluehost/WordPress

MI Genetics Resource Center genetics@michigan.gov

Shotwell, M. 2019 The Misuse of Genetics: The Dihybrid Cross & the Threat of “Race Crossing” American Biology Teacher