Transcript Human Genetics

HUMAN GENETICS
Mutations, Sex-linked traits, Disorders, Pedigrees
What’s a Mutation?
 A change in DNA sequence
 Two types:
 Changes in a single gene
(called gene mutation)
 Changes in a whole chromosome
(called chromosomal mutation)
What’s a Mutation?
 Gene Mutations: Two types…
 1. Point Mutation
 One nucleotide is affected …
that is…
ONE LETTER IS WRONG!
 TTA-GTA-CCG becomes
 TAA-GTA-CCG
(usually changes one amino acid in a protein)
What’s a Mutation?
 Gene Mutations: Two types…
 2. Frameshift Mutation
 Addition or deletion of one letter (nucleotide)
 Sequence is “read” one letter off from correct way
 TTA-GTA-CCG
TTT-AGT-ACC-G
becomes
thesunwashotbuttheoldmandidnotgethishat
What’s a Mutation?
 Chromosomal Mutations
 1. Deletion
 Part of chromosome is missing
What’s a Mutation?
 Chromosomal Mutations
 1. Deletion
 Part of chromosome is missing
 2. Duplication
 Part of chrom. is included twice
What’s a Mutation?
 Chromosomal Mutations
 1. Deletion
 Part of chromosome is missing
 2. Duplication
 Part of chrom. is included twice
 3. Inversion
 Part of chrom. is reversed from usual direction
What’s a Mutation?
 Chromosomal Mutations
 1. Deletion
 Part of chromosome is missing
 2. Duplication
 Part of chrom. is included twice
 3. Inversion
 Part of chrom. is reversed from usual direction
 4. Translocation
 Two non-homologous chrom. exchange portions
Mutagens
 Can alter DNA’s ability to be edited
(corrected)
 Affects gamete and somatic cell formation
 Sources
 Ultraviolet radiation
 Radioactive substances
 X - rays
 Chemical exposure
What’s a Mutation?
 Some mutations are significant and severe,
some are less so, some are never noticed…
 Consider the car…
Sex-Linked Traits
 Sex-linked diseases are X linked…
 The sex chrom. are the X and y
 Consider Hemophilia
(the inability for blood to clot properly)
 Also Colorblindness
(the inability to distinguish certain colors)
Gene that can cause it found on X chrom.
Sex-Linked Traits
 Hemophilia (sex-linked recessive)
 Females/Males:
 XH XH
 XH Xh
 Xh Xh
 XH y
 Xh y
Female, clots
Female, clots (carrier)
Female, can’t clot
Male, clots
Male, can’t clot
Other Disorders
 While mutations are generally gene related
and inherited from one or both parents,
sometimes OTHER reasons cause problems…
 NONDISJUNCTION
 The parent’s genes can be fine. But during
MEIOSIS of the gametes, too many or too few
chromosomes were pulled into the new gamete
cell…
Normal Male Karyotype:
22 sets of autosomes, 1 set of sex chromosomes
Inheritance Patterns
 AUTOSOMAL DOMINANT
 Only one mutated gene on one chrom. is needed
to display the disorder
 AUTOSOMAL RECESSIVE
 Two copies of mutated gene must be present to
display the disorder
 X-Linked DOMINANT
 Mutations on the X chrom. that are dom.
 X-Linked RECESSIVE (like hemophilia)
Pedigrees
 A pedigree chart is a tool used to show all the
known phenotypes of an organism and its
ancestors…
 Used in human genealogy study
Pedigrees
 Let’s build one…