Genetics Pedigrees and Karyotypes
Karyotype
Karyotype
• What to look for in a karyotype?• When analyzing a human karyotype, scientists
first look for these main features:• Are there 46 chromosomes? • Are there 2 identical pairs of each autosome and
2 sex chromosomes? • Are there any rearrangements between
chromosomes or large deletions?
Chromosomes
• Humans have 46 chromosomes
• 44 chromosomes are autosomes
• 2 are sex chromosome• Females have two X
chromosomes• Males have one X and
one small Y chromosome
PedigreesMALEMALE FEMALEFEMALE
Shaded means the person is
“affect” by a disorder
Shaded means the person is
“affect” by a disorder
Unshaded means the person is
not “affect”
Unshaded means the person is
not “affect”
Half shaded means the
person is not “affect”, but is a carrier of the disorder
Half shaded means the
person is not “affect”, but is a carrier of the disorder
Pedigrees MARRIEDMARRIED
THEIR KIDSTHEIR KIDSTHE SON & HIS WIFE
THE SON & HIS WIFE
THEIR KIDSTHEIR KIDS
Inheritance of sex chromosomes
• Egg cells contain one X chromosome
• Sperm cells contain either one X chromosome or one Y chromosome
• So in a human population, half are male and half are female
Sex linked Genes• Genes located on the
sex chromosomes are called sex-linked genes.
• Males have just one X chromosome, so all X-linked alleles are expressed in Males
• What percent of offspring will be girls?
• What percent of offspring will be boys?
• What percent of offspring will have normal vision?
• What percent of offspring will be colorblind?
• What percent of offspring will be carriers?
Sex-Linked Genes
Hemophilia Pedigree
Chromosomal Disorders
• Nondisjunction
Chromosomal Disorders
• Down syndrome– Trisomy 21– Due to non-disjunction
in second stage of meiosis
Chromosomal Disorders
• Turner’s Syndrome
• What is missing?
• Karyotype is (45,X)
• Only one X chromosome
Chromosomal Disorders
• Klinefelter’s Syndrome
• What is extra?
• Karyotype 47 XXY
• Extra X chromosome