Transcript Chapter 7 sections 1,2,4

Chapter 7 sections 1,2,4
Extending Mendelian Genetics
Section 1
 Standard:
 Discuss observed inheritance patterns cause by various modes of
inheritance, including dominant, recessive, codominant, sex-linked,
polygenetic, and multiple alleles.
Section 1: Chromosome and
Phenotype
 Two copies of each
autosomal gene affect
phenotype.
 Autosomal chromosomes do
not play a role in sex
determination.
 You have two alleles for each
gene; one from each parent.
 Most traits are the result of
autosomal genes.
 Curly or straight hair
 Many genetic disorders are
caused by autosomal genes.
 You can predict how likely
someone will be to inherit a
disorder by using a Punnett
Square.
Section 1: Chromosome and
Phenotype
 Disorders caused by recessive
alleles.
 Two copies of the recessive
allele must be present for a
person to have the disorder.
 Often occur when the parents
are heterozygous for the
disorder.
 Cystic fibrosis
 A carrier is someone who
does not show disease
symptoms but has one
recessive allele.
 Allows for lethal disorders to
still show up in the
population’s gene pool
Section 1: Chromosome and
Phenotype
 Disorders caused by dominant
alleles.
 These are far less common
than recessive disorders.
 Huntington’s disease
damages the nervous system
and symptoms only show up
during adulthood.
 50% chance of the offspring
having the disorder if only one
parent carries the trait and
75% chance if both parents
carry the trait.
Section 1: Chromosome and
Phenotype
 Males and females can differ in
sex-linked traits.
 Sex-linked genes
 Genes that are located on sex
chromosomes.
 X and Y chromosomes
 XX=female, XY=male
 Females can only pass on X
and males can pass on either
an X or Y
 X chromosomes have more
influence on phenotype. (has
a lot more genes than the Y
chromosome).
Section 1: Chromosome and
 Expression of Sex-Linked
Genes
Phenotype
 Pattern of expression is
different in sex chromosomes
than in autosomes.
 Males only have one allele
due to only having one X,
while females have two.
 Male express all alleles on
the X.
 Female mammals go through
a process called X
chromosome inactivation.
 One X is randomly “turned
off”
 Due to this females are a
mixture of two types of cells;
one showing mom allele,
one showing dad allele.
 Female calico cats.
Section 2: Complex Patterns of
Inheritance
 Standard:
 Discuss observed inheritance patterns caused by various modes of
inheritance, including dominant, recessive, codominant, sex-linked,
polygenic, and multiple alleles.
Section 2: Complex Patterns of
Inheritance
 Phenotype can depend on
interactions of alleles.
 In incomplete dominance,
neither allele is completely
dominant not completely
recessive.
 Heterozygous phenotype is
intermediate between the
two homozygous phenotypes.
 Homozygous parental
phenotypes not seen in F1
Section 2: Complex Patterns of
Inheritance
 Codominant alleles will both
be completely expressed.
 Codominant alleles are
neither dominant nor
recessive.
 The ABO blood types result
from codominant alleles.
 Many genes have more than
two alleles.
 Blood type
Section 2: Complex Patterns of
Inheritance
 Many genes may interact to
produce one trait.
 Polygenetic traits are
produced by two or more
genes.
 Eye color
 Skin color
Section 2: Complex Patterns of
Inheritance
 An epistatic gene can
interfere with other genes
 In mice fur color is determined
by 5 genes.
 Albinism is a single gene that
can interfere with the
expression of other genes
Section 2: Complex Patterns of
Inheritance
 The environment interacts with
genotypes.
 Phenotype is a combination of
genotype and environment.
 The sex of sea turtles depends
on both genes and the
environment.
 Height is an example of a
phenotype strongly affected
by the environment.
 Poor diet when growing can
stunt your growth.
Section 4: Human Genetics and
Pedigrees
 Standard:
 Discuss observed inheritance patterns caused by various modes of
inheritance, including dominant, recessive, codominant, sex-linked,
polygenic, and multiple alleles.
Section 4: Human Genetics and
Pedigrees
 Human genetics follows the
patterns seen in other
organisms
 The basic principles of
genetics are the same in all
sexually reproducing
organisms.
 Inheritance of many human
traits is complex.
 Single-gene traits are
important in understanding
human genetics.
Section 4: Human Genetics and
Pedigrees
 Females can carry sex-linked
genetic disorders.
 Males (XY) express all of their
sex linked genes.
 Due to them only having one
allele for the trait.
 Expression of the disorder
depends on which parent
carries the allele and the sex
of the child.
 If the father carries the trait
the male offspring will not
have the trait. (father can
only give Y to male offspring,
not the X)
Section 4: Human Genetics and
Pedigrees
 A pedigree is a chart for
tracing genes in a family.
 A pedigree is a chart that can
help trace phenotypes to help
determine genotypes.
 Phenotypes are used to infer
genotypes on a pedigree.
 Autosomal genes show
different patterns on a
pedigree than sex-linked
genes.
Section 4: Human Genetics and
Pedigrees
 If the phenotype is more
common in males, the gene is
likely sex-linked.
 Colorblindness
Section 4: Human Genetics and
Pedigrees
 Several methods help map
human chromosomes.
XY
 A karyotype is a picture of all
chromosomes in a cell
Section 4: Human Genetics and
Pedigrees
 Karyotypes can show changes
in chromosomes.
 Deletion of part of a
chromosome or loss of a
chromosome.
 Large changes in
chromosomes
 Extra chromosomes or
duplication of a part of a
chromosome.