Structural Changes

What are the 2 ways mutations can alter chromosome structure and give examples

• Total amount of genetic information in the chromosome can change

  • EX:

    • Deficiencies/Deletions

    • Duplications

• Genetic material remains the same but is rearranged

  • EX:

    • Inversions

    • Translocations

What are the 5 types of structural alterations?

• Deficiency

• Duplications

• Inversions #ff8e00

• Insertions #8100ff

• Translocation #00d6ff

Deficiency/Deletions

• What

• Phenotypic consequences depends on

• Example

What: When a segment of a chromosome is lost/deleted

Phenotypic consequences depends on:

• Size of deletion

• Chromosomal material deleted

Example: Cri-du-chat syndrome in humans

• Deletion in short arm of chromosome 5

Duplications

• What

• Phenotypic consequences depends on

• More harmful or less than deletions?

What: When a segment of chromosome is copied resulting in extra genetic material

Phenotypic consequences depends on: Size of segment copied

Comparing to deletions: Less harmful

Chromosomal Inversions #ff8e00

• What

• What occurs to the total amount of genetic information

• So is there phenotypic consequences

• How can inversions alter phenotype

• Types

What: When a segment is in reverse sequence along a single chromosome

What occurs to the total amount of genetic information: Stays the same

So is there phenotypic consequences: Mostly no

How can inversions alter phenotype:

• Break point effect (inversion occurs in vital gene)

• Position effect (alters gene expression)

Types:

• Paracentric inversion: Segment of single chromosome breaks in 2 places and flips but centromere not involved

• Pericentric inversion: Segment of single chromosome breaks in 2 places and flips but centromere is involved

Insertion #8100ff

• What

• Examples

What: When a segment of a chromosome is deleted and inserted into another chromosome

Examples: Huntington’s disease and fragile X syndrome

Translocations #00d6ff

• What

• What occurs to genetic material

• Intrachromosomal translocation

• Interchromosomal translocation

  • Types

    • Cause phenotypic consequences?

    • AKA

  • Which one causes phenotypic consequences

    • So they are known as

What: When a segment or a whole arm is exchanged to another chromosome

Intrachromosomal translocation: Segment breaks off and reattaches in a different location on the same chromosome

Interchromosomal translocation: Segment from one chromosome is transferred to another chromosome

• Types of interchromosomal translocations:

  • Reciprocal: segment from 2 different chromosomes have exchanged

    • Cause phenotypic consequences: No because the total amount of genetic material is rearranged only

    • AKA: Balanced translocations (either combinations has all chromosomal material present)

  • Robertsonian: entire chromosome has attached to another chromosome at the centromere (whole arm or centric fusion translocation) and act as one chromosome

    • Cause phenotypic consequences: Can

    • AKA: Unbalanced translocations (either combination is missing material and has extra of other)

Translocations: Robertsonian Translocations #c500ff

• How can it occur

• Most common in

  • Example

• Is it a problem?

• Are there benefits from RT

How it can occur:

• Breaks occur at extreme ends of short arms of 2 nonhomologous acrocentric chromsomes

• Then small acentric fragments are lost

• Larger fragments fuse at centromeric regions to form a single chromosome

• Which is either metacentric or submetacentric

Most common in: Cattle

• 1:29 RT where the long arms of chromosome 1 and 29 fuse at the centromere

• Forming single metacentric chromosome

Is RT a problem: Yes

• Because it causes embryonic death

• So carriers have decreased fertility

Benefits from RT:

• Heifers (young female cows) that take longer to get pregnant (due to RT linked low fertility) continue to grow for longer

• Animals that don’t reproduce early may avoid physical stress of pregnancy and calving too young

Why are majority of these defects not seen frequently in animals?

Because they are incompatible with life

But what are the issues that these defects can cause?

Reproductive problems such as inferitlity, subfertility and intersexuality

Describe the karyotype of a robertsonian translocation cow

• Total chromosomes: 59

  • One fewer as normal cattle have 60 chromosomes

  • Indication of Robertsonian translocation

• Chromosome 1 and 29:

  • Instead of 2 separate acrocentric chromosomes for 1 and 29

  • There’s one large metacentric chromosome labeled as T

• 2 X chromosomes indicate that it’s a female cow

• Final karyotype: 59,XX,rob(1;29)

Describe this karyotype

60,XXY,t(1;29)

What are the results of chromosomal defects?

• Early embryonic death

• Minor to major congenital defects

• Subfertility, infertility or sterility

• Development of cancer