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
Objectives
• Students will be able to:
– 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
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.
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.
7.1 Chromosomes and Phenotype
• Review
– How are dominant-recessive patterns of inheritance in autosomal
chromosomes related to genetic disorders?
– What are the patterns of sex-linked traits?
– How are Mendel’s observations related to genes on autosomes?
– Why are males more likely than females to have sex-linked genetic
disorders?
– How are autosomal traits, including recessive genetic disorders that are
carried in a population, related to Mendel’s observations of heredity?
– Describe how sex-linked genes are expressed differently in males and in
females.
– How might a scientist determine whether a trait is sex-linked by observing
the offspring of several genetic crosses?
– How is the expression of sex-linked genes both similar to and different from
the expression of autosomal genes?
– Scientists hypothesize that over millions of years, the Y chromosome has
lost genes to the X chromosome. During what stages of meiosis might the Y
chromosome have transferred genes to the X chromosome? Explain.