Download 7.1 Chromosomes and Phenotype

Biology Unit Four C –
Chromosomes and Phenotype
Mrs. Pearson’s First Semester Biology
*For those watching by recording, watch for questions on the slides throughout
the presentation. Email me the answers to the questions within two days of the
lesson being presented in order to receive credit for watching the recording.
7.1 Chromosomes and Phenotype
Lesson Objectives
• Discuss nature of sex linked traits
• Discuss factors affecting the expression of phenotypes
7.1 Chromosomes and Phenotype
Getting Rave Reviews…
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Phenotype
Genotype
Recessive
Dominant
Heterozygote
Homozygote
Allele
7.1 Chromosomes and Phenotype
Word of the Day!
• Autosomal
• Any chromosome that is NOT one for determining
whether the organism is male or female.
7.1 Chromosomes and Phenotype
Two copies of each autosomal gene affect phenotype –
How do we know this?
• Mendel studied autosomal
gene traits, like hair texture.
• If a gene is not autosomal,
what is it?
7.1 Chromosomes and Phenotype
• Mendel’s rules of inheritance apply to autosomal genetic
disorders.
– A heterozygote for a recessive disorder is a carrier.
Why?
– Disorders caused by dominant alleles are uncommon.
(dominant)
**Those watching by
recording, include in
your email why it is
uncommon to have a
dominant allele that
causes a disorder.
7.1 Chromosomes and Phenotype
Males and females can differ in sex-linked traits.
• Genes on sex chromosomes are called sex-linked genes.
– Y chromosome genes in mammals are responsible for
male characteristics.
– X chromosome genes in mammals affect many traits –
not just female traits.
7.1 Chromosomes and Phenotype
• Male mammals have an XY genotype.
– All of a male’s sexlinked genes are
expressed – Why?
– Males have no
second copies of
sex-linked genes.
**Those watching by recording,
include in your email why all of a
male’s sex linked genes are
expressed.
7.1 Chromosomes and Phenotype
• Female mammals have an XX genotype.
– Expression of sex-linked genes is similar to autosomal
genes in females – why?
– X chromosome inactivation randomly “turns off” one X
chromosome.
7.2 Complex Patterns of Inheritance
Phenotype can depend on interactions of alleles.
• In incomplete dominance, neither allele is completely
dominant nor completely recessive – what might a
heterozygous individual look like?
– Heterozygous phenotype is intermediate between
the two homozygous phenotypes
7.2 Complex Patterns of Inheritance
• Codominant alleles will both be completely expressed.
What might that look like?
– Codominant
alleles are
neither
dominant nor
recessive.
– The ABO blood
types result
from
codominant
alleles.
• Many genes have more than two alleles.
7.2 Complex Patterns of Inheritance
Many genes may interact to produce one trait.
• Polygenic traits are
produced by two or
more genes.
Order of dominance:
brown > green > blue.
7.2 Complex Patterns of Inheritance
The environment interacts with genotype – think of a
way the environment may affect phenotype.
• 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.
**Those watching by recording, include in
your email why height is strongly affected by
environment.
7.2 Complex Patterns of Inheritance
Review
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Two copies of each autosomal gene affect phenotype
Males and females can differ in sex-linked traits\
Phenotype can depend on interactions of alleles
In incomplete dominance, neither allele is completely
dominant nor completely recessive
• Codominant alleles will both be completely expressed
• Many genes may interact to produce one trait
• The environment interacts with genotype
7.1 Chromosomes and Phenotype
Questions?