Chapter 6 - Pedigree

What are the constraints on studying human genetics?

controlled mating isn't possible, long generation time, and small family size

Pedigree

pictorial representation of a family history that outlines the inheritance of one or more characteristics

Proband

the person for whom the pedigree is initiated

Characteristics of autosomal recessive traits

appear equally among the sexes, both sexes can transmit the trait to their offspring, skips generations, affected offspring are usually born to unaffected parents

What makes autosomal recessive traits appear more frequently

incest

When both parents are heterozygous, autosomal recessive traits affect what proportion of their offspring?

1/4

Characteristics of autosomal dominant traits

affect both sexes equally, both sexes can transmit the trait to their offspring, doesn't skip generations, affected offspring must have an affected parent, unaffected parents do not transmit the trait

When one parent is heterozygous for an autosomal dominant trait and the other is unaffected, what proportion of the offspring will be affected?

half

Characteristics of X-linked recessive traits

usually more males than females affected, skips generations, never passed from father to son

How do x-linked recessive traits transmit from father to daughter?

all daughters of affected fathers are carriers

How do x-linked recessive traits transmit from mother to son?

affected sons are usually born to unaffected mothers, half of a carrier mother's sons are affected

How do x-linked recessive traits transmit from father to son?

they don't

How can a woman be affected by an x-linked recessive trait?

her father has to be affected and her mother must be either a carrier or affected

Characteristics of X-linked dominant traits

affects more females than males, doesn't skip generations

How do x-linked dominant traits pass to daughters?

daughters must have either an affected father or an affected mother

How do x-linked dominant traits pass to sons?

affected sons must have an affected mother

Characteristics of y-linked traits

only males affected, passed from father to all sons, doesn't skip generations

Amniocentesis

using an ultrasound and a needle, amniotic fluid is collected. Fetal cells are isolated and expanded. Tests can then be performed on the cultured cells.

When can amniocentesis be performed?

15-20 weeks into pregnancy

Chorionic villus sampling

a catheter is inserted into the outer layer of the placenta to get chorion cells which can be tested without culturing

pros and cons of chorionic villus sampling

can be done early in pregnancy but can cause placental abruption