Karyotype and Chromosomal Mutation Notes

What is a karyotype? A karyotype is a picture of chromosomes found in a typical human body cell. The karyotype is the result of a haploid sperm cell, carrying 23 chromosomes fertilizing a haploid egg cell, carrying 23 chromosomes.

A Normal Human Karyotype The chromosomes in a human karyotype are arranged in homologous pairs. The first 22 pairs of chromosomes are called autosomes. The 23rd pair of chromosomes are known as the sex chromosomes.

Chromosomal Mutation B. Chromosomal mutations involve changes in the number or structure of chromosomes. Such mutations may change the locations of genes on chromosomes, and may even change the number of copies of some genes.

Chromosomal mutations occur during crossing over. The exchange of genetic material between homologous pairs of chromosomes  

IV. Chromosomal Mutation C. Four types of chromosomal mutations: Deletion Duplication Inversion Translocation

1) Deletion

2) Duplication

3) Inversion

4) Translocation

IV. Chromosomal Mutation D. Deletions involve the loss of all or part of a chromosome E. Duplications produce extra copies of all or part of a chromosome F. Inversions reverse the direction of parts of chromosomes G. Translocations occur when part of a chromosome break off and attach to another chromosome.

IV. Chromosomal Mutation H. Most mutations are neutral – they do not change the expression of genes or proteins. I. Some are harmful, some are beneficial.

Nondisjunction J. Nondisjunction occurs during meiosis when homologous chromosomes fail to separate. Nondisjunction means “not coming apart”. When it occurs, abnormal numbers of chromosomes may find their way into gametes (sperm or egg), and a disorder of chomosome numbers may result.

Nondisjunction

Chromosomal Disorders

Down’s Syndrome Defect – autosomal disorder (extra copy of chromosome 21) Symptoms: Have delayed mental and social development. Common problems may include: Impulsive behavior Poor judgment Short attention span Slow learning

Down’s Syndrome Neither! Due to nondisjunction. Disorder is also called trisomy 21. Have an extra 21st chromosome. Dominant or Recessive? Neither! Due to nondisjunction.

Down’s Syndrome Interesting Facts: It is usually the egg that provides the extra copies of chromosome 21 The older the mother, the chances of having a baby with Down’s Syndrome increases Age 20, 1 in 1500 Age 40, 1 in 60

Patau Syndrome- Trisomy 13 Symptoms Cleft lip or palate Clenched hands (with outer fingers on top of the inner fingers) Close-set eyes -- eyes may actually fuse together into one Decreased muscle tone Extra fingers or toes (polydactyly) Low-set ears Scalp defects (missing skin) Seizures Skeletal (limb) abnormalities Intellectually Disabled

Turner’s Syndrome- XO Symptoms: May be intellectually disabled, some have normal IQ Short stature Sterile (cannot have kids) Webbed neck Underdeveloped breasts and ovaries Defect: XO (missing a sex chromosome)

Turner’s Syndrome- XO Frequency: 1 in 2,500 Interesting Fact: Caused by non-disjunction. (Occurs in meiosis when the sister chromatids aren’t pulled apart.

Klinefelter’s Syndrome- XXY Symptoms: Underdeveloped testes Inability to produce sperm Muscle structure, fat and hair distribution similar to that of a female Breasts develop Defect: XXY-Male with an extra X chromosome in some cells

Klinefelter’s syndrome Eggs Sperm Dominant or recessive – chromosomal mutation XXY Frequency – 1 in 400 males Interesting fact – often goes undiagnosed. Caused by nondisjunction. Can be treated with male hormones.

Double Y syndrome- XYY Signs and symptoms: Often less than average IQ Tall High levels of male hormones Large ears Sunken chest Delayed speech and language skills Defect: Chromosomal mutation - XYY Frequency: 1 in 250 males Interesting fact: Questionable connection to violent tendencies