4 Human inheritance (2015)

Human inheritance In this lesson we will describe the inheritance of traits due to dominant and recessive genes, located on autosomes and sex-chromosomes. We will learn how to determine the mode of inheritance of a given genetic disorder using pedigree analysis. Lesson overview

Human inheritance Some human traits have simple inheritance patterns like the traits that Gregor Mendel studied in pea plants. Other human traits have more complex inheritance patterns. How Mendelian traits are inherited depends on whether the traits are controlled by genes on autosomes or the X and Y chromosomes. Mendelian Inheritance in Humans

Human inheritance Human chromosomes 22 pairs of autosomes 2 sex chromosomes

Mammals: female has two X chromosomes, male has one X and one Y. Birds: female has one Z and one W, male has two Z chromosomes. Human inheritance Genetic determination of sex

Human inheritance Autosomic traits Capacity to roll the edges of the tongue

Human inheritance Autosomic traits

Human inheritance X-linked traits Color blindness (Daltonism) is a x-linked recessive trait

Human inheritance Many genetic disorders are caused by mutations in one or a few genes. Some of the disorders are caused by mutations in autosomal genes, others by mutations in X- linked genes. In both cases, the allele responsible for the disease can be either recessive or dominant. Genetic disorders

Sue and John Sue and John are planning to start a family. They visit a genetic counselor seeking advice about a genetic disease that both John’s and Sue’s families are suffering from. There is no genetic test for this trait. Its onset, which can be gradual, occurs after age 40. Both John and Sue are in their early 30’s. They would like to determine the chances of their children inheriting the disease. 1. What are the possible genotypes of John and Sue? 2. If you are John and Sue’s genetic counselor, how would you explain the chances of their children inheriting the disease?

In a pedigree analysis, information about family members is summarized in a special kind of diagram. Each individual is represented by a symbol, a square for a male and a circle for a female. Individuals who have the trait of interest are represented by black squares or circles. Human inheritance

Pedigree analysis and inheritance (part 1) Woody Guthrie Huntington desease Human inheritance

Males and females are equally likely to have the trait. There is male to male transmission. Traits do not skip generations (generally). If the trait is displayed in offspring, at least one parent must show the trait. If parents don't have the trait, their children should not have the trait (except for situations of gene amplification). The trait is present whenever the corresponding gene is present (generally). If both parents possess the trait, but it is absent in any of their offspring, then the parents are both heterozygous ("carriers") of the recessive allele. Homozygotes for the dominant condition have a more severe form of the condition. Pattern of autosomal dominant trait

Pedigree analysis and inheritance (part 2) Albinism Human inheritance

Males and females have the same chance of expressing the trait You can only express the trait if you are homozygous If both parents express the trait, then all their offspring should also express the trait If the offspring express the trait but their parents don't, then both parents are heterozygous If one parent expresses the trait, then their offspring who don't express it are heterozygous The trait can skip generations Pattern of autosomal recessive trait

Hemophilia is a x-linked recessive trait Human inheritance

The trait is more common in males than in females. If a mother has the trait, all of her sons should also have it. There is no male to male transmission. It has the same inheritance patterns as autosomal recessive for human females. The son of a female carrier has a 50 percent chance of having the trait. Mothers of males who have the trait are either heterozygous carriers or homozygous and express the trait. Pattern of x-linked recessive trait

Sue pedigreeJohn pedigree 1. What are the possible genotypes of John and Sue? 2. If you are John and Sue’s genetic counselor, how would you explain the chances of their children inheriting the disease?