Transcript Ch.14 - Jamestown School District

Unit 4 Genetics
Ch. 14 The Human Genome
Human Chromosomes
 To analyze chromosomes, biologists
photograph cells in mitosis
 They then cut out the chromosomes from
the photograph, & group them together in
pairs
Human Chromosomes
 Karyotype - a picture of chromosomes
arranged in pairs
Human Chromosomes
 Sex chromosomes - 2 of the 46
chromosomes, that determine an
individual’s sex
– Females: XX
– Males: XY
 Autosomes - remaining 44 chromosomes
Human Traits
 Pedigree - chart that shows the relationships
within a family
Human Traits
 Remember that the phenotype of an
organism is determined by its genotype
 Also, that environmental effects on gene
expression are not inherited, genes are
Human Genes
 The human genome, our complete set of
genetic information, includes 10’s of 1000’s
of genes
 The DNA sequences on these genes carry
information for specifying many
characteristics
Human Genes
 Many genetic disorders are caused by
autosomal recessive alleles
Human Genes
 However, some genetic disorders may be
caused by a dominant allele
 Ex.) Dwarfism, Huntington’s Disease (loss of
muscle control, & mental function until death
occurs)
From Gene to Molecule
 In cystic fibrosis, & sickle cell disease, a
small change in the DNA of a single gene
affects the structure of a protein, causing a
serious genetic disorder
From Gene to Molecule
 Cystic fibrosis is caused by the deletion of 3
bases in the DNA of a single gene
– As a result, the body does not produce a protein
needed to transport chloride ions
– CF causes serious digestive & respiratory
problems
Cystic Fibrosis
From Gene to Molecule
 Sickle cell disease is common in African
Americans
– It is characterized by the bent & twisted shape
of the red blood cells
– The cells get stuck in the capillaries, damaging
cells, tissues, & organs
– It causes physical weakness, & damage
to the brain, heart, & spleen (may be fatal)
Human Genes & Chromosomes
 Genes located close together on the same
chromosome are linked, so they tend to be
inherited together
 Linked genes may be separated, however,
during crossing-over
Sex-Linked Genes
 Sex-linked genes - genes located on the sex
chromosomes
 Males have 1 X chromosome,
therefore, all X-linked alleles are
expressed in males, even if they
are recessive
Sex-Linked Genes
 Ex. of sex-linked disorders: colorblindness,
hemophilia, muscular dystrophy
Chromosomal Disorders
 Nondisjunction - when homologous
chromosomes fail to separate during
meiosis
 If it occurs, abnormal #’s of
chromosomes could find their
way into gametes, & a disorder of
chromosome #’s may result
Chromosomal Disorders
 Down Syndrome results when there is an
error on chromosome 21
Human DNA Analysis
 DNA Fingerprinting - (Gel Electrophoresis),
analyzes sections of DNA that vary from 1
individual to another
DNA Fingerprinting
The Human Genome Project
 The Human Genome Project is an ongoing
effort to analyze the human DNA sequence
 Biotechnology companies are rushing to find
genetic info. that may be used
in developing new drugs &
treatments for diseases
Gene Therapy
 In gene therapy, an absent or faulty gene is
replaced by a normal, working gene
 Viruses are often used because they can
enter cells so easily
Ethical Issues in Human
Genetics
 The goal of biology is to gain a better
understanding of the nature of life
 As our knowledge increases, so does our
ability to change the genetics of living
things, including humans
 What will happen to the human species if we
design our bodies?