Chapter 7 Extending Mendelian

Genetics

Karyotype = picture of all chromos in cell

They can show a change in chromos whether autosomal or sex-linked

Autosomal recessive disorders take 2 copies of the recessiveEx. Albinism

Ex. Cystic fibrosisEx. Tay-Sachs disease

A carrier has 1 recessive, doesn’t show symptoms

Autosomal dominant disorders less common, only take 1 dominantEx. Achondroplasia

(dwarfism)Ex. Huntington’s disease

Sex linked genes (those on X & Y) also affect inheritance

Since males have 1 X (XY) they show all alleles on X (even recessive)

Ex. Color blindness is more common in men 3 genes on X chromo

Females are carries for sex-linked disorders

Ex. Queen Victoria carried the allele for hemophilia (on X) passed on to many in royal family

Not all alleles follow the dominant vs. recessive pattern

Ex. Red flowers x white flowers = pink flowers

Incomplete dominance = neither allele is completely dominant

Heterozygous shows a blend of the traits

Codominance = both alleles are expressed

Ex. Speckled chicken

Heterozygous shows both traits

Human example of codominance = blood type

Controlled by 3 allels; IA, IB, i

IA and IB are codominant, i is recessive

Also an example of multiple alleles

Polygenic trait = trait controlled by 2 or more genes Ex. Skin color in humans

is controlled by 4 genes

Ex. Human eye color is controlled by at least 3 genes

Phenotypes can also be affected by the environment (nutrition, exercise, health care)

A pedigree chart = genetic family tree (shows genos and phenos)

Squares = males; circles = females

Shaded in = has trait; not shaded = no trait

Pedigrees can be used to determine genotype based on whether the trait is autosomal or sex-linked, dominant vs. recessive