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Uncover the inheritance patterns and complexities of human genetics using a combination of methods such as pedigree analysis. Understand sex-linked traits, autosomal genes, and chromosome mapping techniques through practical examples like Queen Victoria’s hemophilia.
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KEY CONCEPT A combination of methods is used to study human genetics.
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
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.
Females can only show the trait if both alleles are recessive ( Xh Xh ) • Females can be a carrier if heterozygous ( XH Xh )
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.
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
If the phenotype is more common in males, the gene is likely sex-linked.
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
Queen Victoria – Hemophilia • Sex-Linked recessive
X Y Several methods help map human chromosomes. • A karyotype is a picture of all chromosomes in a cell.
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