Genetics Lecture 4

pedigree

• diagram listing members and ancestral relationships in a family

• used to study heredity

pedigree allows us to determine if trait is:

• dominant or recessive

• located on X or Y chromosome or autosome

• located on mitochondria

male pedigree symbol

square

female pedigree symbol

circle

autosomal dominant trait on pedigree

disease appears for at least one person in each generation

characteristics of autosomal dominant traits

• heterozygotes have abnormal phenotype

• every affected individual has at least one affected parent

• male and females are equally affected

if an affected individual with an autosomal dominant trait is heterozygous and mates with an unaffected individual, what is the percent chance of their child being affected?

50%

autosomal recessive traits

• most individuals have unaffected parents for rare traits

• all children of affected parents are affected

• affects males and females

• can skip generations if rare

inheritance of X and Y chromosomes for males and females

• males pass X chromosome to daughters and Y chromosomes to sons

• females pass X chromosomes to daughters and sons

what happens if a male inherits the X-linked recessive allele?

he expresses the X linked recessive phenotype

X linked dominant traits

• affected males have all affected daughters and no affected sons

• twice as many daughters are affected than sons

Y linked traits

• passed from male to male

• infertility is only Y linked trait

hemizygous

• having one copy of a gene instead of two

• all males because they only have one X chromosome

why are males usually more affected for X-linked traits

because they are hemizygous

mitochondrial inheritance

maternally inherited through cytoplasm of egg

how many genes do mitochondria have?

37 genes

what are genetic disorders in mitochondria often associated with?

energy conservation

penetrance

all or none expression of genotype

expressivity

severity or extent of gene’s phenotypic expression

genetic heterogenity

when mutations in different genes cause the same phenotype

complementation

• for phenotype that expresses genetic heterogeneity

• dominant allele from one parent can mask mutated gene from other parent