Genetic Processes: Sex-Linked Inheritance and Mutations

SBI3U (Secours)

Sex-Linked Inheritance and Transmission

transmission of genetic characteristics when they are carried on the X chromosomes

3 terms for describing the appearance of a sex-linked gene (the phenotypes)

1) Affected: characteristic manifests itself/is visible

2) Carrier: not affected, but have the gene

3) Unaffected: does not have the gene

In general, sex-linked diseases are:

recessive

which sex is more likely to be carriers, and which are more likely to be affected?

Carriers: females, because they have two X chromosomes

Affected: males, because they only have one X chromosome, so if the allele is present, they will have the disease

Pedigree

a diagram that illustrates the genetic relationship in a group of related individuals

another word for pedigree

genealogical tree

On a pedigree, _____ shapes are used for males, and _____ shapes are used for females

squares, circles

On a pedigree, if an individual is completely shaded in, they are ________. If they are ½ shaded, they are ______. If they are not shaded, they are _________.

affected, carriers, unaffected

On a pedigree, _____ are indicated with roman numbers, and _____ (including birth order) are indicated with arabic numbers.

generations, individuals

In human pedigrees, genotypes can only be _______ from the _____, they cannot always be determined with complete certainty.

inferred, phenotypes

the four main inheritance types

1. autosomal recessive

2. autosomal dominant

3. sex-linked recessive

4. sex-linked dominant

Autosomal Recessive features

• traits will often skip a generation

• parents can pass it on to offspring as carriers

• male and female equally affected

• both parents can be carriers

Autosomal Dominant features

• no skipping of generations (everyone with the dominant allele is affected)

• there will not be carriers

• almost all individuals will be heterozygous

• male and female equally affected

Sex-Linked Recessive features + examples

• fathers can only pass on traits to daughters, not sons (carried on x chromosome)

• sons can only recieve the trait from their mother

• males are more likely to be affected

ex: hemophilia, colour-blindness, muscular dystrophy

Sex-Linked Dominant features + examples

• similar to sex-linked recessive, except females will be affected if they recieve even 1 dominant allele

• affected fathers will pass it down to daughters but not sons (again, carried on x chromosome)

ex: Fragile-X syndrome, vitamin-D resistant rickets

Mutation

A change in DNA that has a positive, negative, or neutral effect

What can cause genetic mutations?

• Induced Mutations: environmental factors

• Spontaneous Mutations: random errors during DNA replication, repair, or recombination

If cancer was caused by carcinogens (ex: smoking, sunlight), can it be passed down? Why?

No, they cannot. This is because only certain cells are affected, usually not the sex cells.

When will a mutation be passed down?

If the mutation occured in a germ/sex cell

5 types of mutations

1. Deletion

2. Duplication

3. Inversion

4. Insertion

5. Translocation

Identify the mutation:

deletion

Identify the mutation:

duplication

Identify the mutation:

inversion

Identify the mutation:

insertion

Identify the mutation:

translocation

Identify all mutations:

deletion, duplication, inversion, insertion, translocation

Silent mutation

A mutation where the code changes, but the resulting amino acid does not (neutral effect)

Depending on the magnitude/size of the mutation, it is considered either:

Large scale mutation or point mutation

Large Scale Mutation

An entire portion of the chromosome is altered (rare)

Point Mutation

A small scale change in the sequence of the nitrogenous bases

⇨ Frame-Shift: a kind of insertion or deletion, where one of more nucleotides are added/deleged