Transcript Section 1 Chromosomes and Inheritance

Chapter 12
Section 1 Chromosomes
and Inheritance
Objectives
• Distinguish between sex chromosomes and autosomes.
• Explain the role of sex chromosomes in sex determination.
• Describe how an X- or Y-linked gene affects the inheritance of
traits.
• Explain the effect of crossing-over on the inheritance of genes
in linkage groups.
• Distinguish between chromosome mutations and gene
mutations.
Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomes
• Genes reside on chromosomes.
Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomes, continued
• Sex Chromosomes and Autosomes
– Sex chromosomes contain genes that determine
an organism’s sex (gender).
– The remaining chromosomes that are not directly
involved in determining the sex of an individual are
called autosomes.
Chapter 12
Section 1 Chromosomes
and Inheritance
Karyotypes: Male and Female
Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomes, continued
• Sex Determination
– In mammals, an individual carrying two X
chromosomes is female.
– An individual carrying an X and a Y chromosome
is male.
• Sex of an offspring is determined by the
male/father
Chapter 12
Section 1 Chromosomes
and Inheritance
Genetic Research – Early Work
• Thomas Hunt Morgan – early 1900’s
– Compiled research by using small fruit fly Drosophila
melanogaster
– While conducting his research he crossed a white-eyed
(recessive) male with a normal red-eyed female.
• The F1 generation all had red eyes, but when the F1
generation were crossed together the ratio became 3 redeyed to 1 white-eyed
– This shows evidence of crossing-over, but it doesn’t
show until the F2 generation
– Exactly like Mendel’s pea plant diagram pg. 175
Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location
• Sex-Linked Genes and Traits
– Genes found on the X chromosome are X-linked
genes.
– A sex-linked trait is a trait whose allele is located
on a sex chromosome.
– Because males have only one X chromosome, a
male who carries a recessive allele on the X
chromosome will exhibit the sex-linked trait.
• If a characteristic is sex-linked is occurs mostly in males
Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location, continued
• Linked Genes
– Pairs of genes that tend to be inherited together
are called linked genes.
• Colorblindness is sex-linked
Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location, continued
• Chromosome Mapping
– The farther apart two genes are located on a
chromosome, the more likely a cross-over will
occur.
– Researchers use recombinant percentages to
construct chromosome maps showing relative
gene positions.
Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location, continued
• Chromosome Maps:
– Depict the linear sequence of genes on a
chromosome
– Are constructed using crossing-over data from
mating experiments
– Are practical with species having only a few
chromosomes
Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations
• Germ-cell mutations occur in gametes and can be
passed on to offspring.
• Somatic-cell mutations occur in body
cells and affect only the individual organism.
ex. Certain types of human skin cancers
and leukemia result from somatic-cell
mutations, but can’t be passed on to
offspring to be inherited
Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations
• Lethal mutation cause death, often before death
• Effects of a mutation can be helpful, harmful, and/or
neutral
Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations, continued
• Chromosome Mutations
– Chromosome mutations are changes in the
structure of a chromosome or the loss or gain of
an entire chromosome.
Chapter 12
Section 1 Chromosomes
and Inheritance
Deletion: loss of a piece of
a chromosome due to
breakage
Chromosomal Mutations
Inversion: chromosomal
segments break off, flips
around backward, and
reattaches
Translocation: piece of
one chromosome breaks
off and reattaches to a
nonhomologous
chromosome
Fig 12-6 pg 239
Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations, continued
• Nondisjunction: a
chromosome fails to
separate from its homologue
during meiosis. One gamete
receives an extra copy of a
chromosome and another
gamete receives no copies.
• This occurs with Down
syndrome, a person with it
has 3 copies of chromosome
#21, which gives them 47
chromosomes total instead
of 46
http://img.dailymail.co.uk/i/pix/2007/07_02/gardinerDM1907_468x380.jpg
Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations, continued
• Gene Mutations
– Gene mutations are changes in one or more of the
nucleotides in a gene.
Chapter 12
Gene Mutations
Section 1 Chromosomes
and Inheritance
Chapter 12
Section 2 Human Genetics
Objectives
• Analyze pedigrees to determine how genetic traits and
genetic disorders are inherited.
• Summarize the different patterns of inheritance seen in
genetic traits and genetic disorders.
• Explain the inheritance of ABO blood groups.
• Compare sex-linked traits with sex-influenced traits.
• Explain how geneticists can detect and treat genetic
disorders.
Chapter 12
Section 2 Human Genetics
Inheritance of Traits
• Pedigrees
– Geneticists use pedigrees to trace diseases or
traits through families.
– Pedigrees are diagrams that reveal inheritance
patterns of genes.
Chapter 12
Section 2 Human Genetics
Pedigree for Cystic Fibrosis
Chapter 12
Some Important
Genetic
Disorders
Genetic Disorder:
disease or
disabling condition
that have a
genetic basis
Section 2 Human Genetics
Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders
• Single genes having 2 or more alleles can determine
traits, such as blood type or cystic fibrous
• Polygenic Inheritance
– Geneticists have learned that most human
characteristics are polygenic characteristics (they
are influenced by several genes)
– Ex. Skin color results from additive effect of 3-6
genes
– Other Ex. Eye color, height, and hair color
Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• Complex Characters
– Complex characters, such as polygenic traits,
are influenced by both genes and environment.
– Ex. Skin color is influenced by genes and if
person lives in area with a lot of sun, the
skin will naturally be darker
– Ex. Height is influenced by genes and if the
person has good nutrition and no diseases
they should be taller than someone who has
poor nutrition and diseases
Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• Multiple Alleles
– Multiple-allele characters, such as ABO blood
groups, are controlled by three or more alleles of a
gene.
» Look at top of page 244
Chapter 12
Section 2 Human Genetics
Comparing Single Allele, Multiple Allele,
and Polygenic Traits
Click below to watch the Visual Concept.
Visual Concept
Chapter 12
Section 2 Human Genetics
Comparing Complete, Incomplete,
and Co-Dominance
Click below to watch the Visual Concept.
Visual Concept
Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• X-Linked Traits
– The gene for colorblindness, an X-linked recessive
gene, is found on the X chromosome.
Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• Sex-influenced Trait
– A sex-influenced trait, such as pattern baldness, is
expressed differently in men than in women even
if it is on an autosome and both sexes have the
same genotype.
• The difference is due to higher levels of
testosterone in men, which interacts with genotype
to produce pattern baldness
Chapter 12
Section 2 Human Genetics
Comparing X-Linked and Sex-Influenced Traits
Click below to watch the Visual Concept.
Visual Concept
Chapter 12
Section 2 Human Genetics
Detecting Genetic Disease
• Genetic screening examines a person’s genetic
makeup and potential risks of passing disorders to
offspring.
• Amniocentesis and chorionic villi sampling help
physicians test a fetus for the presence of genetic
disorders.
Chapter 12
Section 2 Human Genetics
Detecting Genetic Disease, continued
• Genetic Counseling
– Genetic counseling informs screened individuals
about problems that might affect their offspring.
– Process uses family pedigree to look at family
history of disease and can assist parents in
deciding whether or not to have children
Chapter 12
Section 2 Human Genetics
Treating Genetic Disease
• Genetic disorders are treated in various ways.
• Among the treatments are symptom-relieving
treatments and symptom-prevention measures, such
as insulin injections for diabetes.
Chapter 12
Section 2 Human Genetics
Genetic Disorder
Click below to watch the Visual Concept.
Visual Concept
Chapter 12
Section 2 Human Genetics
Treating Genetic Disease, continued
• Gene Therapy
– In gene therapy, a defective gene is replaced with
a copy of a healthy gene.
– Somatic cell gene therapy alters only body cells.
– Germ cell gene therapy attempts to alter eggs or
sperm.