Genetic Mutations

Mutations

• New inherited traits, or mutations, may appear in a strain of plant or animal.

• The first individual showing the new trait iscalled a mutant.

2 Types of Mutations

1) Chromosomal mutations•An abnormal change in the structure

of all or part of a chromosome or in the number of chromosomes an organism has.• For example, an organism can be

missing a part of a chromosome or have 1 added to it’s total number.

2 Types of Mutations

2) Gene mutations•A change that affects a gene on a chromosome•Example could be a gene that creates a disease in an organism.

How Mutations are Inherited

•For a mutation to be inherited it must be present in the DNA of a gamete. The mutation must occur in a gamete or in any cell from which a gamete develops. Cannot be transmitted from body (somatic) cells.

How Mutations Happen

•Mutations occur naturally at a low rate. They are usually the result of random errors in replication of the DNA.• This can account for differences in DNA of

identical twins, especially during gestation.• If environmental factors cause a mutation,

the factor is called a mutagen. (eg x-rays, UV light, food preservatives, food colorings, etc.)

Mutation from UV Light

Chromosomal Mutations – 3 Kinds•1. Changes in Chromosome Structure• Chromosome structure may

become permanently altered during meiosis when chromatids become entangled and their parts rearranged. (Not the same as crossing over)

Types of Changes in Chromosomal Structure • Four types:• Translocation – transfer of a part of a chromosome

to a non-homologous chromosome• Inversion – piece of the chromosome is rotated

which reverses the order of genes• Addition – piece of a chromosome breaks off and

attaches to a homologous chromosome which causes some genes to be repeated• Deletion – piece of the chromosome breaks off

resulting in a loss of some genes.•

Mutations from X-Rays

Chromosomal Point Addition Syndrome

• Fragile X syndrome is caused when a spot on the X chromosome contains a stretch of nucleotides in which a small part of the chromosome is repeated (as many as 400 times).

• This causes a constriction in the x chromosome making it quite fragile.

• Males who inherit this X chromosome are mentally retarded. Females are only mildly affected.

Chromosomal Mutations – 3 Kinds

2) Nondisjunction• The addition or loss of a whole

chromosome.•Happens when chromosomes that

normally separate during meiosis remain together.

Interphase

Prophase I

Metaphase 1

Anaphase 1

Telophase 1

Prophase 2

Metaphase 2

Anaphase 2

Telophase 2

Haploid Cells at the end of Meiosis 2

Non-Disjunction Types • Monosomy refers to a condition in which there is one

chromosome is missing. It is abbreviated 2n - 1.

• For example, monosomy X is a condition in which cells have only one X chromosome.

• Trisomy refers to a condition in which there is one extra chromosome and is abbreviated 2n + 1.

• Trisomy 21 is an example of a trisomy in which cells have an extra chromosome 21.

Non-Disjunction Types

• Monosomies and trisomies usually result from nondisjunction during meiosis but can also occur in mitosis. They are more common in meiosis 1 than meiosis 2.• They are generally lethal except monosomy X (female

with one X chromosome) and trisomy 21 (Down’s Syndrome).• Affected individuals have a distinctive set of physical and

mental characteristics called a syndrome. For example, trisomy 21 is Down syndrome.

Some common chromosomal abnormalities:•Abnormality Karyotype•Down Syndrome Trisomy 21• Turner Syndrome X• Triple-X Syndrome XXX•Klinefelter Syndrome XXY• Jacob Syndrome XYY

Karyotypes

Down Syndrome Karyotype Turner Syndrome Karyotype

Triple X Syndrome

• Triple X syndrome, also called trisomy X or 47,XXX, is characterized by the presence of an additional X chromosome in each of a female's cells. • Although females with this condition may be

taller than average, this chromosomal change typically causes no unusual physical features. •Most females with triple X syndrome have

normal sexual development and are able to conceive children.

Triple X Syndrome

• Triple X syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. • Delayed development of motor skills (such as sitting and

walking), weak muscle tone (hypotonia), and behavioral and emotional difficulties are also possible, but these characteristics vary widely among affected girls and women. • Seizures or kidney abnormalities occur in about 10

percent of affected females.

Triple X Syndrome Karyotype

Klinefelter Syndrome

•Klinefelter's syndrome, 47, XXY, or XXY syndrome is a condition in which human males have an extra X chromosome. • The condition exists in roughly 1 out

of every 1,000 males. One in every 500 males has an extra X chromosome but does not have the syndrome.

Klinefelter Syndrome

• The principal effects are development of small testicles and reduced fertility.•A variety of other physical and

behavioral differences and problems are common, though severity varies and many boys and men with the condition have few detectable symptoms.

Klinefelter Syndrome Karyotype

Jacob’s Syndrome

• Jacob's syndrome is a rare chromosomal disorder that affects males. •Males with Jacob's syndrome, also

called XYY males.• Jacob's syndrome occurs when a male

inherits two Y chromosomes from his father instead of one.

Jacob’s Syndrome

• There are many symptoms associated with Jacob's Syndrome. The most common symptoms are: • learning problems at school• delayed emotional maturity•Males with Jacob’s syndrome are tall, thin,

have acne, speech problems, and reading problems.

Jacob Syndrome Karyotype

Turner Syndrome

• Turner syndrome is caused by monosomy X (absence of an entire sex chromosome). • Occurring in 1 in 2000 – 1 in 5000 females,

the syndrome has a number of varied side effects. • There are characteristic physical

abnormalities, such as ‘short stature, swelling, broad chest, low hairline, low-set ears, and webbed necks.

Turner Syndrome

• Girls with Turner syndrome typically experience non-working ovaries, which results in an absence of menstrual cycle and sterility. Other health concerns are also frequently present, including ‘congenital heart disease, hypothyroidism, diabetes, vision problems, hearing concerns, and many autoimmune diseases.• Cognitive deficits that are common with

particular difficulties in visuospatial, mathematical, and memory areas.

Down Syndrome Video • http://www.youtube.com/watch?v=5M--xOyGUX4