13.1 Ecologists Study RelationshipsUnit 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 sex-linked 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 sex-linked genes are expressed.

– Males have no second copies of sex-linked genes.

7.1 Chromosomes and PhenotypeMAIN IDEAS • 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.