Download Chromosomes and Phenotype

Chromosomes and Phenotype
KEY CONCEPT
The chromosomes on which genes are located can
affect the expression of traits.
Chromosomes and Phenotype
Autosomes
• Autosomes are:
– All chromosomes other than – Mendel studied autosomal
sex chromosomes
gene traits like hair texture
– Do not directly determine an – Two (2) copies of each
organism’s sex
autosomal gene affect
phenotype
Chromosomes and Phenotype
Autosomal gene expression:
• Two (2) alleles that interact to produce a phenotypic trait
• Mendel’s rules of inheritance apply to autosomal genetic
disorders.
• Complete the Punnett square in
the notes using this one…
– A heterozygote for a
recessive disorder is a
carrier.
– Disorders caused by
dominant alleles are
uncommon.
(dominant)
Chromosomes and Phenotype
Sex Chromosomes
• Sex chromosomes are:
The genes that determine
an organism’s sex
– Y chromosome genes
in mammals are
responsible for male
characteristics.
– X chromosome genes
in mammals affect
many traits.
Chromosomes and Phenotype
Inheritance of sex chromosomes: Complete the Punnett square
in the notes using this one…
Chromosomes and Phenotype
Inheritance of sex chromosomes: (nothing for notes)
• Genes on sex chromosomes are called sex-linked genes.
• Males and females can differ in sex-linked traits
Meow.
Chromosomes and Phenotype
Expression of sex-linked genes in males:
• Sex linked genes are genes on the sex chromosomes
• Male mammals have an XY genotype.
– All of a male’s sexlinked genes are
expressed.
– All sex-linked genes
are expressed
because there is no
2nd allele that could
mask the 1st allele
Chromosomes and Phenotype
Expression of sex-linked genes in females:
• Sex linked genes are genes on the sex chromosomes
• 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.
Chromosomes and Phenotype