Honors Biology CH 9 Notes

Chromosomal Mutations

What is a mutation?

Changes in the genetic material (DNA). A feature of DNA.

Mutations can occur in two different types of cells:

1. Somatic (body) cells

2. Gamete (sex) cells

Mutations that occur in somatic (body) cells usually result in killing

that body cell only.

An exception to this is if the mutation occurs to the DNA that controls regulation of the cell cycle. This can result in cancer.

• Somatic mutations usually do NOT affect future individuals.

• Somatic mutations can NOT be passed on to the next generation.

Mutations that occur in gamete (sex) cells means that every cell of the developing fetus/baby will have that mutation.

• Gamete mutations usually do affect the individual with some genetic disorder.

• Gamete mutations can be passed on to the next generation.

There are two types of mutations that can occur in

gamete cells:

1. Gene Mutations

2. Chromosomal Mutations

CHROMOSOMAL MUTATIONS

• Multiple congenital anomalies (deformities)

• Occur during pregnancy, present at delivery

• Usually not inherited

5 types of Chromosomal Mutations:

1. Deletion

2. Duplication

3. Inversion

4. Translocation

5. Non-disjunction

Deletion

Involves the loss of part of a chromosome.

Interstitial Deletion

Terminal deletion

Deletion

• TWO TYPES OF DELETIONS:

• End missing (terminal)• Piece within

chromosome missing (interstitial)

Terminal deletion of p 5 Cri du Chat Syndrome = Cry of the Cat

•“Happy puppetsyndrome”•Low IQ•Abnormal gait•Inappropriately happy

Maternal15q11-13

Deletion of Paternal 15q11-13

Deletion of Paternal 15q11-13

Duplication

Involves the production of extra copies of parts of the chromosome.

Duplication

• 4 copies of the top of chromosome 22• Mental retardation in all babies

•Over sized babies•Over sized organs•Too much mitosis!•Insulin-like growth factor not turned off because two paternal alleles for chromosome11p

Inversion

Reverses the direction of parts of a chromosome.

Inversion

• Around the centromere

• Above or below the centromere

Two types of inversions

Paracentric Inversion:• An inversion in which

breakpoint occur on one arm of the chromosome.

• Does not span the centromere.

Pericentric Inversion:• An inversion in which

breakpoints occur on both arms of the chromosome.

• Includes the centromere.

Inversion

Also an inversion

Translocation

When one part of a nonhomologous chromosome breaks off and attaches to another chromosome.

Robertsonian Translocation

• A type of translocation in which two nonhomologous acrocentric (have centromeres near their ends) chromosomes break at their centromeres. The long arms become attached to a single centromere and serve a function. The short arms also join containing nonessential genes and is lost within a few cell divisions. (long arms fuse and short arms are lost.)

About one in a thousand newborns has a Robertsonian translocation. The most frequent forms of Robertsonian translocations are between chromosomes 13 and 14, 13 and 21, and 21 and 22.

• A Robertsonian translocation in balanced form results in no excess or deficit of genetic material and causes no health difficulties.

In unbalanced forms, Robertsonian translocations cause chromosomal deletions or duplication and result in syndromes of multiple malformations.

Translocations can be either balanced or unbalanced depending if genetic material is lost.

Translocation

A Robertsonian translocation

All essential genetic material is present so the children appear

normal

Most common birth defects with unbalanced translocations of 11 and 22 are cleft palate, heart defects, ear anomalies, and male genital defects.

Errors in Chromosomal Separation

Non-disjunction

Means “not coming apart”.

When homologous chromosomes fail to separate properly during anaphase 1 of meiosis.

• Results in abnormal numbers of chromosomes.

• Trisomy means a person has an extra copy of a chromosome.

• Monosomy means a person is missing a copy of a chromosome.

Normal female

Normal male

Trisomy means a person has an extra copy of a chromosome

•3 of chromosome 21

Non-disjuction: Trisomy

• Chromosome 18 does not separate properly during meiosis.

• This gives the child three parts of chromosome 18.

• Also called Trisomy 18

Edward’s Syndrome

•1/3000 births•Mental Retardation•Failure to thrive•Heart defect•Overlapping fingers•Low set, fawn-like ears

• three of chromosome 13 present

• These individuals are males.

• Little body hair is present.

• Typically tall.

• Some development of breast tissue normally seen in females.

• May or may not have evidence of mental retardation.

Monosomy means a person is missing a copy of a chromosome.

• These individuals are female• Underdeveloped ovaries• Individuals are sterile and lack expected

secondary sexual characteristics• Short stature, webbed/bull neck, broad

chest• Mental retardation typically not evident.

Turner’s Syndrome Baby•Only one X chromosome present

Turner’s Syndrome age 12

• Karyotyping

• Fluorescent (FISH)