1. Chromosomal Basis of Inheritance
Tracing Heredity through Inheritance of Specific Chromosomes

2. Sex Determination
Sex Chromosomes: homologous chromosomes that differ in size and genetic composition between males and females
Human
Chromosome X Y
Size and gene number
Larger
2142 genes
Smaller
326 genes
Genetic
Composition
Multiple genes unrelated
to gender
Single gene influences gender: TDF = testis
determining factor

3. Sex Determination
Autosome: any chromosome that is not a sex chromosome
Humans have 22 pairs of autosomes and 1 pair of sex chromosomes

4. Human Karyotype showing
homologous chromosome pairs

5. Phenotypic Ratio of Offspring
Sex Determination
Female Male
XX x XY
½ X ½ X
½ X
½ Y
¼ XX
¼ XX
¼ XY
¼ XY
Phenotypic Ratio of Offspring
½ Female + ½ Male

6. X-linked Genes Hemophilic Male Non-hemophilic Female
(father is hemophilic)
XhY x XHXh
½ XH ½ Xh
¼ XHXh
¼ XhXh
½ Xh
½ Y
¼ XHY
¼ XhY
Phenotypic Ratio of Offspring
¼ hemophilic males + ¼ non-hemophilic males
¼ hemophilic females + ¼ non-hemophilic females

7. Terms Specific to Sex-linked Genes
Females
Homogametic: only X found in gametes
Can be homozygous or heterozygous for traits on X-chromosome
Males
Heterogametic: either X or Y in gametes
Hemizygous for traits on the X-chromosome

8. Patterns of Inheritance
Autosomal Dominant
Autosomal Recessive
X-linked Dominant
X-linked Recessive
Y-Linked Inheritance

9. Pedigree for Huntington’s Disease,
an Autosomal Dominant Trait

10. Pedigree for Albinism, an Autosomal Recessive Trait

12. Pedigree for Colorblindness,
an X-linked Recessive Trait