1. DNA2. Gene

4. Genome

5. Individual

3. Chromosome7. Population

6. Family (pedigree)

Cell

Human Genetics

A karyotype is a set of photographs of chromosomes grouped in ordered pairs.

Human Chromosomes• We get 23 pairs of chromosomes.

• One set from our mom, and one set from our dad, for a total of

46 chromosomes.

Sex Chromosomes• The first 44 chromosomes are

known as autosomes.

• The last 2 are called sex chromosomes because they determine an individual’s sex.

• Females are XX.• Males are XY.

What is the probability that a newborn will be male or female?

XX XX

XY XY

Female (XX) X X

XMale (XY)

Y

1 2

A pedigree is a chart that shows the relationships within a family.

Circle = femaleSquare = male

Horizontal line connecting a male and female = marriage

Vertical line and a bracket connect the parents to their children

Half-shaded circle or square = person is a carrier of the trait

Completely shaded circle or square = person expresses the trait.

Circle or square that is not shaded = person neither expresses the trait nor is a carrier of the trait.

Section 14-1

Figure 14-3 A PedigreeUnderstanding a Pedigree

Insert 10-15 on study guide.

Homologous chromosomes fail to separate

Meiosis I:Nondisjunction

Meiosis II

Section 14-2

NondisjunctionNondisjunction

Nondisjunction is an error in meiosis in which chromosomes fail to separate

Chromosomal Disorders• Monosomy occurs when one

chromosome from a pair is missing.

• Trisomy occurs when there is an extra, or third, chromosome for one pair.

Trisomy 21(Down’s Syndrome)

Trisomy XXY(Klinefelter’s Syndrome)