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

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 humantraits is complex. • Single-gene traits areimportant in understandinghuman genetics. Widow’s Peak 

3. Y X 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.

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

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