Bio 106

Lecture 12

Genetics and Man

A. Cytogenetics

B. Inborn Errors of Metabolism

C. Behavioral Genetics

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cytogenetics

The study of chromosome number, structure, function,

and behavior in relation to gene inheritance, organization and

expression

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cytogenetics

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cytogenetics

Variations in chromosome number: Euploidy – normal number and sets of chromosomes

Polyploidy - 3 or more complete sets of chromosomes

Aneuploidy – presence of additional or missing individual chromosomes

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cytogenetics Common Types of Polyploidy

Triploidy: 3n = 3(23) = 69

Tetraploidy: 4n = 4(23) = 92

Pentaploidy: 5n = 5(23) = 115

and so on………

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cytogenetics

Common Types of Aneuploidy: • Monosomy – one less chromosome (23 x 2) – 1 = 45 • Trisomy – one additional chromosome (23 x 2) + 1 = 47

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cytogenetics Monosomy X (45,X)

Turner Syndrome -named after Henry Turner

(amenorrhea)

(webbing)

(cubitus valgus)

(Coarctation of aorta)

1 out of 2500 female live births

Sex Chromosome Variations

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Turner Syndrome - Signs and symptoms may vary significantly, probably

showing prenatally or at birth or during infancy and even during teen and adult years of a female

- Other causes (aside from monosomy): 1. Mosaicism – due to errors in cell division during early fetal

development; chromosomal change in only some of the cells

2. Y chromosome material present in some cells together with the X chromosome (while some cells have only 1 copy of the X chromosome)

cytogenetics

- Family history doesn't seem to be a risk factor.

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Turner Syndrome

cytogenetics

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Trisomy 21 (standard)

Down Syndrome - named after John Langdon Down

cytogenetics

1 in 700 births

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cytogenetics

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Trisomy 21 - one of the most common causes of human birth defects

- symptoms vary from person to person and can range from mild to severe

• Persons with this condition have an increased risk of certain types of leukemia, which can also cause early death.

• The level of intellectual disability varies, but is usually moderate. Adults with Down syndrome have an increased risk of dementia.

cytogenetics

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Types of Down Syndrome: 1. Trisomy 21 - ~95% of the cases 2. Translocation Down syndrome ~3%

- occurs when an extra part or a whole extra chromosome 21 is present, but it is attached or “translocated” to a different chromosome rather than being a separate chromosome 21.

3. Mosaic Down syndrome: affects about 2% of the people with Down syndrome

cytogenetics

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cytogenetics Trisomy 18 Edwards Syndrome -named after John Hilton Edwards

1 in 5000 to 1 in 7000

births

More females affected

Mean life expectancy:

4 days

-Congenital heart defects -Growth retardation -Dysmorphic features -Facial clefts -Spina bifida -Severe developmental delay

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Trisomy 18 types: 1. Full trisomy 18 - ~95% of the cases

2. Partial trisomy 18 – very rare

3. Mosaic trisomy 18 – very rare

cytogenetics

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cytogenetics

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cytogenetics Trisomy 13 Patau Syndrome -named after Klaus Patau

1 in 12000 births

Mean life expectancy:

130 days

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cytogenetics

1 in 12000 births

Mean life expectancy:

130 days

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Trisomy 13 types: 1. Trisomy 13

2. Mosaicism

3. Partial trisomy 13

cytogenetics

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cytogenetics

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cytogenetics Trisomy 8 Mosaicism Syndrome (T8mS) -also known as Warkany syndrome after Dr Josef Warkany

1 in 25000 to 50000

births

A pear-shaped, bulbous nose with upturned nostrils, a protruding lower lip and large ears.

Stiff joints with a limited range of movement; clenched or bent fingers and/or toes; deep palm and sole creases; occasionally under-developed nails; missing or small kneecaps typically have mild to moderate intellectual disabilities.

•Most cases have mosaicism •Large ears, deep plantar furrows •Spina bifida, renal and ureteral anomalies, CHD •Increased risk of hematologic malignancy

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cytogenetics

Sex Chromosome Variations

Trisomy X (47,XXX)

•Incidence 1 in 1000 female births •Above average stature •Normal phenotype •Most have learning disabilities •Behavior problems common •Many never diagnosed

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cytogenetics Sex Chromosome Variations

Klinefelter Syndrome (47,XXY) •1:1000 male births

•Tall stature •Gynecomastia •Hypogonadism •Infertility •Learning disabilities •Problems with socialization •Many never diagnosed

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cytogenetics

Klinefelter Syndrome (47,XXY)

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cytogenetics Sex Chromosome Variations Jacob Syndrome (47, XYY)

•1/1000 newborn males •Tall stature •Most phenotypically normal •Normal IQ but 50% have learning disabilities (language and speech)

•Many never diagnosed

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cytogenetics

Jacob Syndrome (47, XYY) Most males with 47,XYY syndrome

have normal sexual development and are able to father children.

Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), hand tremors or other involuntary movements (motor tics), and behavioral and emotional difficulties are also possible.

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Factors that influence non-disjunction or premature sister chromatid separation: Age Recombination events

•The rate of Down syndrome and other trisomies increases with maternal age.

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Inborn errors of metabolism Lactase deficiency:

- common in adults; occurs more often in Native Americans and people of Asian, African, and South American descent than among people of European descent.

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Inborn errors of metabolism

PKU -AR - PKU is rare, estimated to affect 1 in every 10,000 babies born in the UK.

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Inborn errors of metabolism

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Inborn errors of metabolism Classic Galactosemia (GALT deficiency) - also known as type I, is the most common and most severe form of the condition. -occurs in 1 in 30,000 to 60,000

newborns -Autosomal recessive on chromosome 9p13 with male=female

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Behavioral genetics

An interdisciplinary field of study concerned with the genetic basis of

behavior and personality.

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Behavioral genetics

Both genes and environment interact to shape human behavior.

• The fundamental issue is how much a role genetics do play in shaping human behaviors.

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Behavioral genetics

• Genes do not directly produce behaviors.

• They produce proteins that increase the probability that a behavior will develop under certain circumstances.

• Genes can also have an indirect effect. – Genes can alter your environment by producing

behaviors or traits that alter how people in your environment react to you.

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Behavioral genetics

• Evolutionary psychology (sociobiology) focuses upon functional explanations of how behaviors evolved.

• Assumes that behaviors characteristic of a species have arisen through natural selection and provide a survival advantage. – Examples: differences in peripheral/color vision,

sleep mechanisms in the brain, eating habits, temperature regulation.

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Behavioral genetics

• Some behaviors are more debatable regarding the influence of natural selection. – Examples:

• Life span length

• Gender differences in sexual promiscuity

• Altruistic behavior

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Behavioral genetics

• twin studies remain one of the best ways of identifying genetic markers linked to complex behavioral traits

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Behavioral genetics Correlations for IQ scores MZ twins reared together 0.86 MZ twins reared apart 0.79 DZ twins reared together 0.60 Siblings reared together: 0.47 Parent and Child: 0.40 Foster parent and child at age 7: 0.31

– At age 18: 0.00 Siblings reared apart: 0.24

Cousins: 0.15

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Behavioral genetics

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Some behavioral disorders that are influenced by genes:

1. Alcoholism

2. Schizophrenia

3. depression

Behavioral genetics

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1. Alcoholism

Behavioral genetics

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1. Alcoholism

Behavioral genetics

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2. Schizophrenia

Behavioral genetics

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3. Depression

Behavioral genetics

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