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