Dunn M&C - Beyond Mendel

sex linkage, pedigrees, etc.

incomplete dominance

looks like the blending hypothesis of inheritance.

• e.g, the deep purple/pink allele of the flower color gene is incompletely dominant over the white allele

codominance

occurs when two alleles are phenotypically expressed simultaneously; in other words, heterozygotes express both phenotypes

Codominance

occurs when two alleles are phenotypically expressed in equal measure; in other words, heterozygotes express both phenotypes

APO blood groups

illustrates multiple alleles, IA, IB, i allele

IA allele

causes the surface glycoprotein to be modified by a red sugar

IB allele

causes the surface glycoprotein to be modified by a blue sugar

i allele

does not cause any modification (not blue or red sugar added)

polygenic traits

those determined by two or more genes

• e.g, hair color, skin color, eye color, height

• most considered complex, influenced by environmental factors such as diet.

autosomes

non-sex chromosomes

normal human karyotype

44 autosomes and 2 sex chromosomes

X & Y chromosome during meiosis

act as homologous pairs

• 50% of sperm contain X and 50% of sperm contains Y chromosomes

nondisjunction of sex chromosomes

leads to viable aneuploidies

aneuploidy

The occurrence of one or more extra or missing chromosomes in a cell or organism

reciprocal crosses

a cross in one in which you switch the sex of the parent affected by a phenotype.

• sex-linked inheritance patterns can be observed by different outcomes of this

mutations in x-linked genes

results in predominantly male diseases (X-linked diseases)

pedigrees

document the inheritance of traits in human families

• squares are males, circles are females

• lines between people mean that they mated

• filled square/circle = affected with a particular phenotype like a disease

patterns of inheritance

describe how traits are passed from parents to offspring, with common patterns including autosomal dominant, autosomal recessive, and X-linked inheritance.

Pedigree of an autosomal dominant allele causing a disease trait

brachydactyly example

pedigree of an autosomal receessive allele causing a disease trait

albinism is autosomal

• the trait may skip one or more generations

• females and males are equally likely to be affected.

• Individuals may have unaffected parents.

• Affected individuals often result from mating between relatives, typically first cousins.

X-linked recessive traits

observed virtually exclusively in males and are often passed through unaffected females

autosomal dominant example

autosomal recessive example