Download Chapter 12-Inheritance Patterns and Human Genetics

Chapter 12-Inheritance
Patterns and Human
Genetics
Section 1
Chromosomes and Inheritance
Objectives
Understand gene expression and how the
genetic code is universal to almost all
organisms
Explain how mutations in DNA sequence
may or may not result in phenotypic
change
Explain how mutations in gametes may
result in phenotypic changes in offspring
Chromosomes and Inheritance
Section 1
In the early 1900’s Thomas Morgan began work on
small fruit flies.
Discovered they have four pairs of chromosomes
3 pairs were the same size in both male and female
1 pair differed in size and shape
Females have 2 identical chromosomes called Xchromosomes
Males have 1 X-chromosome and 1 Y-chromosome
These chromosomes are called sex chromosomes
Gene Expression
Gene expression- the activation or “turning on” of a
gene that results in transcription and the production
of mRNA.
Genetic code- the term for the rules that relate how a
sequence of nitrogenous bases in the nucleotides
corresponds to a particular amino acid
Why is this important???
Ever heard of genome?
Effects of Gene
Location
Sex linked trait- refers to a trait that is coded for by
an allele, that is located on a sex chromosome
X-chromosome larger than the Y
More X-linked traits than Y-linked
There are some genes that are inherited together.
These are linked genes
What causes mutations?
Mutations can be caused by several factors.
Replication errors can cause mutations.
Mutagens, such as UV ray and chemicals, can
cause mutations.
Some cancer drugs use mutagenic properties to
kill cancer cells.
Mutagens
Mutagen-is a physical or chemical agent that changes
the genetic material, usually DNA, of an organism
and thus increases the frequency of mutations above
the natural background level.
Mutagens are therefore also likely to be carcinogens.
They can cause cancer
Mutations
A change in the nucleotide-base sequence from a
gene or DNA molecule
Types of mutations
Germ-cell--occur in an organism’s gametes
Don’t affect the organism itself
Somatic-cell– take place in an organism’s body cells
Can affect the organism
Lethal mutations
Cause death, often before birth.
Some mutations can cause beneficial phenotypes
Chromosome Mutations
Deletion- the loss of a piece of a chromosome due to
breakage
Chromosome Mutations
Inversion- a chromosomal segment breaks off, flips
around backward, and reattaches
Chromosome Mutations
Translocation- a piece of one chromosome breaks off
and reattaches to a nonhomologous chromosome.
Chromosome Mutations
Nondisjuntion- a chromosome fails to separate from
its homologue during meiosis
Think about an extra copy of a chromosome, another
gamete doesn’t receive one. Down Syndrome
2 copies of chromosome at chromosomes 21
Polyploidy
It is the phenomenon of having more than two sets
of chromosomes or genomes. Polyploidy occurs in
nature due to the failure of chromosomes to
separate at the time of anaphase either due to
nondisjunction or due to non-formation of spindle.
In humans this will always result in death
Gene Mutations
Point Mutation- the substution, addition, or removal
of a single nucleotide
Occurs within a single gene or other segment of DNA
on a chromosome.
3 types of genetic mutations
Substitution
Frameshift mutation
Insertion mutation
Gene Mutations
Substitution- one nucleotide replaces another
Gene Mutations
Frameshift mutations- occurs when a single
nucleotide is deleted and the remaining sequences
shift to replace missing base.
Gene mutations
Insertion mutations- one or more nucleotides are
added to a gene.
another version of frameshift mutation
Section 2
Human Genetics
Learn about genetic disorders
The phenotype of an offspring might be affected by
gamate mutation
Do you guys remember Phenotype?
What causes mutations?
Genetic Disorders
Inheritance of Traits
Pedigrees
a diagram that shows how a trait is inherited over
several generations
Genes, mutations and
Phenotypes, oh my
Mutations may or may not affect phenotype.
Chromosomal mutations tend to have a big
effect.
Some gene mutations change phenotype.
A mutation may cause a premature stop codon.
A mutation may change protein shape or the
active site.
A mutation may change gene regulation.
Mutations aren’t all bad
Some gene mutations do not affect phenotype.
– A mutation may be silent.
– A mutation may occur in a noncoding region.
– A mutation may not affect protein folding or the
active site.