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 X- chromosomes 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.