AP Biology 2006-2007

Genetic Disorders

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Chromosomal abnormalities Incorrect number of chromosomes

nondisjunction chromosomes don’t separate properly

during meiosis breakage of chromosomes

deletion duplication inversion translocation

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Nondisjunction Problems with meiotic spindle cause errors in

daughter cells homologous chromosomes do not separate

properly during Meiosis 1 sister chromatids fail to separate during Meiosis 2 too many or too few chromosomes

2n n

n

n-1

n+1

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Alteration of chromosome number

AP Biologytrisomy

2n+1

Nondisjunction Baby has wrong chromosome number

trisomy cells have 3 copies of a chromosome

monosomy cells have only 1 copy of a chromosome

n+1 n

monosomy2n-1

n-1 n

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Human chromosome disorders High frequency in humans

most embryos are spontaneously aborted alterations are too disastrous developmental problems result from

biochemical imbalance imbalance in regulatory molecules?

Certain conditions are tolerated upset the balance less = survivable characteristic set of symptoms = syndrome

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Box #1 What are two causes of

nondisjunction? What is the outcome?

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Down syndrome Trisomy 21

3 copies of chromosome 21 1 in 700 children born in U.S.

Chromosome 21 is the smallest human chromosome but still severe effects

Frequency of Down syndrome correlates with the age of the mother

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Down syndrome & age of mother

Mother’s ageIncidence of

Down Syndrome

Under 30 <1 in 1000

30 1 in 900

35 1 in 400

36 1 in 300

37 1 in 230

38 1 in 180

39 1 in 135

40 1 in 105

42 1 in 60

44 1 in 35

46 1 in 20

48 1 in 16

49 1 in 12

Rate of miscarriage due to amniocentesis: 1970s data

0.5%, or 1 in 200 pregnancies

2006 data<0.1%, or 1 in 1600 pregnancies

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Genetic testing Amniocentesis in 2nd trimester

sample of embryo cells stain & photograph chromosomes

Analysis of karyotype

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Sex chromosomes abnormalities Human development more tolerant of

wrong numbers in sex chromosome But produces a variety of distinct

syndromes in humans XXY = Klinefelter’s syndrome male XXX = Trisomy X female XYY = Jacob’s syndrome male XO = Turner syndrome female

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XXY male one in every 2000 live births have male sex organs, but

are sterile feminine characteristics

some breast development lack of facial hair

tall normal intelligence

Klinefelter’s syndrome

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Klinefelter’s syndrome

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Jacob’s syndrome male XYY Males

1 in 1000 live male births

extra Y chromosome slightly taller than

average more active normal intelligence, slight learning disabilities delayed emotional immaturity normal sexual development

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Trisomy X XXX

1 in every 2000 live births produces healthy females

Why? Barr bodies

all but one X chromosome is inactivated

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Turner syndrome Monosomy X or X0

1 in every 5000 births varied degree of effects webbed neck short stature sterile

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Box #2 Describe two types of sex chromosome

abnormalities

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Changes in chromosome structure deletion

loss of a chromosomal segment

duplication repeat a segment

inversion reverses a segment

translocation move segment from one chromosome

to another

err

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ne

rro

r o

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AP Biology

Certain human genetic disorders can be attributed to the inheritance of single gene traits or chromosomal changes.

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Sickle cell anemia is a hereditary blood disorder caused by a single nucleotide substitution that results in abnormally shaped hemoglobin.

• Fatigue• Rapid heart rate• Strokes• Painful joints• Delayed growth

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Sickle cell disease is more common in those of African descent, due to heterozygote advantage. (People who are heterozygous for sickle cell have less chance of acquiring malaria.)

HAHA Normal blood cells

HAHS Heterozygote; less

likely to get malaria

HSHS Sickle cell disease

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Box #3 What are the advantages and

disadvantages of the sickle cell trait

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Huntington’s disease is an autosomal dominant disorder that causes degeneration of the nervous system. Affected individuals usually begin showing symptoms at 35-40.

• Hallucinations• Psychosis• Dementia• Jerking movements• Confusion• Rigidity• Death

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Color blindness is caused by a sex-linked recessive mutation. Because of this, males are twice as likely to inherit this trait as females.

• Trouble seeing colors and the brightness of colors.

• Trouble differentiating between shades of the same color or similar colors.

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Tay-Sachs disease is an autosomal recessive disorder of the nervous system, more prevalent in the  Ashkenazi Jewish population.

• Deafness• Blindness• Dementia• Eventual

paralysis• Seizures• Death, usually

before age 4 or 5.Cherry-red spot

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Many ethical, social and medical issues surround human genetic disorders.

Genetic screening for Tay-Sachs

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Ethical Considerations of Genetics Testing:

Possible discrimination by employers or health insurers

The need for ethical standards for work with human research subjects or tissues

Consideration of social, cultural and religious perspectives on genetics and health

Marketing of genetics tests Informed consent

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Box #4 Describe your stance on genetic

testing.

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The Human Genome Project sequenced the entire human genome.

An international collaboration between hundreds of labs in the United States, the UK, Japan, France, Germany and Spain.

Began in 1990; completed in 2000. Mostly funded by the US Department of

Energy, National Institute of Health and private interest groups.

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The Human Genome Project can help us understand diseases by:

Genotyping of specific viruses to direct appropriate treatment Identification of oncogenes and mutations linked to

different forms of cancer The design of medication and more accurate prediction of

their effects Advancement in forensics Biofuels and other energy applications; agriculture, Comparative sequencing to establish evolutionary

relationships (such as BLAST) The commercial development of genomics research

related to DNA based products (a multibillion dollar industry).

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Box #5 Describe the purpose of the human

genome project.

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 Historical Ethical, Legal, and Social Issues (ELSI) of Genetics

Eugenics advocates improving

human hereditary traits through

selective reproduction of more desired people and traits, and reduced

reproduction of less desired people and

traits.

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Sterilization Laws were practiced by many states during the 1900s.

Compulsory sterilization of mental health patients

Men sterilized to treat aggression and criminal behavior

Coerced sterilization of many ethnic groups

The American eugenics movement was the model for Nazi eugenics policies.

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Amniocentesis  is a medical procedure used in prenatal diagnosis of chromosomal abnormalities. A small amount of amniotic fluid, which contains fetal tissues, is sampled and the fetal DNA is examined for genetic abnormalities. The test is usually performed between the 15th – 20th week of pregnancy.

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Amniocentesis can lead to Selective Reduction of Multiple Embryos

Nadya Suleman , known as Octomom in the media, is an

American woman who came to international attention when she gave birth to octuplets in

January 2009. Suleman octuplets are only the second full set of octuplets to be born alive in the United States. The

circumstances of their high order multiple birth have led to

controversy in the field of assisted reproductive technology as well as an

investigation by the Medical Board of California of the fertility specialist involved.

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Actress Angelia Jolie made the headlines when she underwent a prophylactic mastectomy after finding out that she was genetically predisposed to breast cancer.

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The Genetic Information Nondiscrimination Act of 2008, also referred to as GINA, is a new federal law that protects Americans from being treated unfairly because of differences in their DNA that may affect their health. The new law prevents discrimination from health insurers and employers.

The Genetic Information Nondiscrimination Act (GINA)

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Can a gene be patented? Not according to the US Supreme Court.

• In Association for Molecular Pathology vs. Myriad Genetics, Inc., the Supreme Court ruled that a natural gene cannot be patented. However, synthetic genes, such as cDNA are patentable. (June 2013)

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Box # 6 Do you agree with the supreme courts

decision? Explain

AP Biology 2006-2007

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