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)