1 Chapter 11 Complex Inheritance and Human Heredity 11.3 Chromosomes and Human Heredity

2 Karyotype Studies Karyotype is a micrograph (picture) of chromosomes at metaphase arranged by size in homologous pairs. Karyotype is a micrograph (picture) of chromosomes at metaphase arranged by size in homologous pairs. Twenty-two pairs of autosomes are the same for males and females. Twenty-two pairs of autosomes are the same for males and females. Males have one X chromosome and one Y chromosome (not paired) and females have two X chromosomes (paired). Males have one X chromosome and one Y chromosome (not paired) and females have two X chromosomes (paired). Karyotypes are useful for detecting chromosome abnormalities Karyotypes are useful for detecting chromosome abnormalities

3 Karyotype Studies Chromosome smearKaryotype

4 Telomeres Telomeres protective end caps on the chromosomes made of DNA and proteins. Telomeres protective end caps on the chromosomes made of DNA and proteins. Short repetitive nonessential DNA sequences Short repetitive nonessential DNA sequences Prevent one chromosome form binding to another chromosome (not sticky) Prevent one chromosome form binding to another chromosome (not sticky)

5 Telomeres Absolutely essential for chromosome function Absolutely essential for chromosome function Telomeres decrease in size (length) as an organism ages and may play a role in aging and cancer. Telomeres decrease in size (length) as an organism ages and may play a role in aging and cancer. Cancer cells have increased length of telomeres compared to adult cells. Cancer cells have increased length of telomeres compared to adult cells. Telomere function is an intense field of research Telomere function is an intense field of research

6 Nondisjunction Failure of chromosomes to separate during cell division Failure of chromosomes to separate during cell division Results in one cell getting too many chromosomes and one cell not getting enough. Results in one cell getting too many chromosomes and one cell not getting enough. If nondisjunction occurs during meiosis the resulting gametes could form an organism with every cell having an incorrect chromosome number. If nondisjunction occurs during meiosis the resulting gametes could form an organism with every cell having an incorrect chromosome number.

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8 Down Syndrome Results of parental gamete nondisjunction resulting in trisomy (three chromosomes ) of chromosome #21. Results of parental gamete nondisjunction resulting in trisomy (three chromosomes ) of chromosome #21. Symptoms include: mental retardation, distinctive facial features, short stature, heart defects, sexually underdeveloped, sterile, more likely to develop leukemia and Alzheimer's, shorter life span Symptoms include: mental retardation, distinctive facial features, short stature, heart defects, sexually underdeveloped, sterile, more likely to develop leukemia and Alzheimer's, shorter life span

9 Down Syndrome

10 Down Syndrome Incidence of Down Syndrome increases with increasing age of the mother Incidence of Down Syndrome increases with increasing age of the mother Risk increases to 6% for mothers over age 45 Risk increases to 6% for mothers over age 45 Recommended fetal testing for mother’s age 35 and older Recommended fetal testing for mother’s age 35 and older

11 Other Trisomys Patau syndrome: trisomy 13; 1/5000; serious eye, brain and circulatory problems; lifespan less than 1 year Patau syndrome: trisomy 13; 1/5000; serious eye, brain and circulatory problems; lifespan less than 1 year Edward’s syndrome: trisomy 18; 1/10,000; effects every body organ; lifespan less than 1 year Edward’s syndrome: trisomy 18; 1/10,000; effects every body organ; lifespan less than 1 year

12 Nondisjunction of Sex Chromosomes Male Klinefelter syndrome: (XXY); 1/2000; males sex organs, testes abnormally small; sterile; feminine body characteristics (breast enlargement, fat deposition); normal intelligence Klinefelter syndrome: (XXY); 1/2000; males sex organs, testes abnormally small; sterile; feminine body characteristics (breast enlargement, fat deposition); normal intelligence (XYY); taller than average male; not characterized by a “syndrome”; some suggest increased aggression (XYY); taller than average male; not characterized by a “syndrome”; some suggest increased aggression

13 Nondisjunction of Sex Chromosomes Female (XXX): 1/1000; normal due to X inactivitation; only distinguishable by karyotype (XXX): 1/1000; normal due to X inactivitation; only distinguishable by karyotype Turner syndrome Monosomy X (XO): 1/5000; female with no maturation of sex organs; no secondary sex characteristics; short; sterile; normal intelligence with spatial learning disabilities Turner syndrome Monosomy X (XO): 1/5000; female with no maturation of sex organs; no secondary sex characteristics; short; sterile; normal intelligence with spatial learning disabilities

14 Fetal Testing Amniocentesis: removal amniotic fluid with sloughed fetal cells at 14 th -16 th week; for diagnosis of chromosomal abnormalities; 1% risk of complications Amniocentesis: removal amniotic fluid with sloughed fetal cells at 14 th -16 th week; for diagnosis of chromosomal abnormalities; 1% risk of complications

15 Fetal Testing Chorionic villus sampling: removal of placental sample at 8 th -10 th week; quicker results; less accurate; less than 1% risk of complications Chorionic villus sampling: removal of placental sample at 8 th -10 th week; quicker results; less accurate; less than 1% risk of complications

16 Fetal Testing Fetal blood sampling: sample of fetal blood; can detect increased number of genetic abnormalities; medication can be given to fetus before birth; greater risk to fetus Fetal blood sampling: sample of fetal blood; can detect increased number of genetic abnormalities; medication can be given to fetus before birth; greater risk to fetus