Transcript 5-2 genetics summary

How are traits passed
from parents to
offspring?
Understanding Inheritance
• What determines the expression of
traits?
• How can inheritance be modeled?
• How do some patterns of inheritance
differ from Mendel’s model?
Understanding Inheritance
• gene
• heterozygous
• allele
• Punnett square
• phenotype
• incomplete dominance
• genotype
• codominance
• homozygous
• polygenic inheritance
What Controls Traits
• Mendel concluded that two factors—one
from each parent—control each trait.
• Mendel’s “factors” are part of
chromosomes which exist as pairs—one
chromosome from each parent.
• Each cell in an offspring organism
contains chromosomes from both
parents.
What Controls Traits (cont.)
• A gene is a section on a chromosome
that has genetic information for one
trait.
• The different forms of a gene are called
alleles. Each chromosome has one
allele for every gene on it.
• The two chromosomes in an offspring
cell may have the same or different
alleles.
What Controls Traits (cont.)
• Geneticists call
how a trait
appears, or is
expressed, the
trait’s phenotype.
• The two alleles
that control the
phenotype of a
trait are called the
trait’s genotype.
What Controls Traits (cont.)
phenotype
from Greek phainein, means “to
show”
What Controls Traits (cont.)
• When the two
alleles of a gene
are the same, the
genotype is
homozygous.
• If the two alleles of
a gene are
different, the
genotype is
heterozygous.
What Controls Traits (cont.)
Scientists use uppercase and lowercase
letters as symbols to represent the
alleles in a genotype.
How do alleles determine the
expression of traits?
Modeling Inheritance
A Punnett square is a model used to
predict possible genotypes and
phenotypes of offspring.
Modeling Inheritance (cont.)
A pedigree shows phenotypes of
genetically related family members.
Modeling Inheritance (cont.)
How can inheritance be
modeled?
Complex Patterns of Inheritance
• Sometimes traits appear to be blends
of alleles.
• Alleles show incomplete dominance
when the offspring’s phenotype is a
blend of the parents’ phenotypes.
• Codominance occurs when both
alleles can be observed in a
phenotype.
Complex Patterns of Inheritance (cont.)
Some traits, such as human ABO blood
type, are determined by more than one
allele.
Complex Patterns of Inheritance (cont.)
Polygenic inheritance occurs when
multiple genes determine the phenotype
of a trait.
How does polygenic
inheritance differ from
Mendel’s model?
Genes and the Environment
• An organism’s environment can affect
its phenotype.
• Some examples of environmental
factors that affect phenotype are soil
type that a flower is growing in or time
of year that a butterfly develops.
• The genes for traits are located on
chromosomes.
• Geneticists use Punnett squares to
predict the possible genotypes and
phenotypes of offspring.
• In polygenic
inheritance, traits
are determined by
more than one
gene and have
many possible
phenotypes.
What is the name for different
forms of a gene?
A. alleles
B. phenotypes
C. genotypes
D. chromosomes
What is the genotype when two
alleles of a gene are the same?
A. heterozygous
B. dominant
C. homozygous
D. recessive
What occurs when both alleles
can be observed in a phenotype?
A. incomplete dominance
B. homozygous
C. polygenic
D. codominance
Do you agree or disagree?
3. All inherited traits follow Mendel’s
patterns of inheritance.
4. Scientists have tools to predict the form
of a trait an offspring might inherit.