Download 7.1 Chromosomes and Phenotype

13.1 Ecologists Study Relationships
Unit 3: Genetics
Chapter 7 Extending Mendelian Genetics
Section 7-1 Chromosomes and Phenotype
7.1 Chromosomes and Phenotype
KEY CONCEPT
The chromosomes on which genes are located can
affect the expression of traits.
7.1 Chromosomes and Phenotype
MAIN IDEAS
• Two copies of each autosomal gene affect
phenotype.
• Males and females can differ in sex-linked
traits.
7.1 Chromosomes and Phenotype
Objectives
• Relate dominant-recessive patterns of
inheritance in autosomal chromosomes to
genetic disorders.
• Describe patterns of inheritance in sexlinked traits.
7.1 Chromosomes and Phenotype
VOCABULARY
carrier, carrier, p. 201
sex-linked gene, p. 201
X chromosom
inactivation p. 203
7.1 Chromosomes and Phenotype
Two copies of each autosomal gene affect phenotype.
• Mendel studied autosomal
gene traits, like hair texture.
7.1 Chromosomes and Phenotype
• Mendel’s rules of inheritance apply to autosomal genetic
disorders.
– A heterozygote for a recessive disorder is a carrier.
– Disorders caused by dominant alleles are uncommon.
(dominant)
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.
7.1 Chromosomes and Phenotype
• Male mammals have an XY genotype.
– All of a male’s sexlinked genes are
expressed.
– Males have no
second copies of
sex-linked genes.
MAIN IDEAS
7.1
Chromosomes
and Phenotype
• Two
copies of each autosomal
gene affect phenotype.
• Males and females can differ in sex-linked traits.
VOCABULARY
carrier, carrier, p. 201 sex-linked gene, sex-linked gene, p. 201 X
chromosome X chromosome inactivation p. 203
MAIN IDEA
Two copies of each autosomal gene affect phenotype.
Objectives
• Relate dominant-recessive patterns of inheritance in autosomal
chromosomes to genetic disorders.
• Describe patterns of inheritance in sex-linked traits.
7.1 Chromosomes and Phenotype
• Female mammals have an XX genotype.
– Expression of sex-linked genes is similar to autosomal
genes in females.
– X chromosome inactivation randomly “turns off” one X
chromosome.