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 MutationC. Four types of chromosomal mutations:1) Deletion2) Duplication3) Inversion4) 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 SyndromeDefect – 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• 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 13Symptoms• 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- XOSymptoms: • May be intellectually disabled, some have normal

IQ• Short stature• Sterile (cannot have kids)• Webbed neck• Underdeveloped breasts

and ovariesDefect:• XO (missing a sex chromosome)

Turner’s Syndrome- XO Frequency:1 in 2,500Interesting 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 developDefect: XXY-Male with an

extra X chromosome in some cells

Klinefelter’s syndrome

• 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.

Eggs Sperm

Double Y syndrome- XYYSigns 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 malesInteresting fact: Questionable

connection to violent tendencies