1. KEY CONCEPT A combination of methods is used to study human genetics.

2. Human genetics follows the patterns seen in other organisms.
The basic principles of genetics are the same in all sexually reproducing organisms.
Inheritance of many human traits is complex.
Single-gene traits are important in understanding human genetics.
Widow’s Peak 

3. Females can carry sex-linked genetic disorders.
Males (XY) express all of their sex linked genes.
No second X chromosome to mask the X present
Expression of the disorder depends on which parent carries the allele and the sex of the child. X Y

4. Females can only show the trait if both alleles are recessive ( Xh Xh )
Females can be a carrier if heterozygous ( XH Xh )

5. A pedigree is a chart for tracing genes in a family.
Phenotypes are used to infer genotypes on a pedigree.
Autosomal genes show different patterns on a pedigree than sex-linked genes.

6. Tracing Autosomal Genes
Equal numbers of males and females
If the recessive phenotype shows, it must be homozygous
The dominant phenotype can be either homozygous or heterozygous

7. If the phenotype is more common in males, the gene is likely sex-linked.

8. Tracing Sex-Linked Genes
More males than females show the trait
Females must inherit 2 recessive alleles to show up, males need only 1 allele
Heterozygous females are carriers
Female carriers can pass on the recessive allele to either males or females
Males can pass the recessive allele only to female offspring

9. Queen Victoria – Hemophilia
Sex-Linked recessive

10. Several methods help map human chromosomes.
A karyotype is a picture of all chromosomes in a cell.
X Y

11. Karyotypes can show changes in chromosomes.
deletion of part of a chromosome or loss of a chromosome
large changes in chromosomes
extra chromosomes or duplication of part of a chromosome
Trisomy: three
of one
chromosome