Transcript 7.1 Chromosomes and Phenotype

Biology Unit Four C –
Chromosomes and Phenotype
Mrs. Pearson’s First Semester Biology
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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?