Download 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
Two copies of each autosomal gene affect phenotype.
• Genetic traits depend on
dominant and recessive
alleles
• Other factors affect
Phenotypes
– Which chromosome allele
is located on
– Sex chromosome
– Autosomal chromosome
• Mendel studied autosomal
gene traits, like hair texture.
7.1 Chromosomes and Phenotype
• Sexually reproducing organisms have 2 copies of each
gene, one from each parent
– Both chromosomes have same gene, different alleles
Ex. Purple flower vs White flower
7.1 Chromosomes and Phenotype
• Mendel’s rules of inheritance apply to autosomal genetic
disorders.
– They are either recessive or dominant
• One recessive disorder is Cystic Fibrosis
– Is a disease that causes excessive production of
mucus that causes blockage of pancreatic ducts,
intestines, and bronchi, it is fatal
– A heterozygote for a recessive disorder is a carrier.
(dominant)
7.1 Chromosomes and Phenotype
• Dominant disorders are less common
– Huntingtons disease affects the nervous system,
specifically causing brain cells to break down. It
occurs in adulthood, and is fatal.
• Since it occurs in adulthood someone can pass it on to there
children, even before they show symptoms.
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.
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.