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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
Autosomes are body chromosomes
Two copies of each autosomal
gene affect phenotype.
• Mendel studied autosomal
gene traits, like hair texture.
7.1 Chromosomes and Phenotype
• Autosomal gene expression
– A heterozygote for a recessive disorder is a carrier.
– Disorders caused by dominant alleles are uncommon.
(dominant)
7.1 Chromosomes and Phenotype
Sex chromosomes are XX (girl) or XY (boy).
• Genes on sex chromosomes are called sex-linked genes.
– Sex linked disorders are linked to the X chromosome
• Hemophilia, Colorblindness and ALD are all sex linked.
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
– Example: XhY.
7.1 Chromosomes and Phenotype
• Female mammals have an XX genotype.
– Expression of sex-linked genes is similar to autosomal
genes in females.
– Example : XHXH