Epistasis, Polyploidy, Karyotypes, and Pedigrees Chapter 11

Epistasis- Gene interactions One gene interferes with the expression of another. In many animals, coat color is often determined by epistatic interactions of genes. E- gene for pigment and B- gene for depositing coat color. eebb eeB_ E_bb E_B_ No dark pigment present in fur Dark pigment present in fur

Polyploid y Those containing more than two paired (homologous) sets of chromosomes One or more extra sets of chromosomes. Always lethal in humans Earthworms and goldfish can sometime be polyploidy. Wheat (6n), oats (6n), sugar cane (8n)

Karyotypes

Normal Karyotype

Non- Disjunction Cell division during which sister chromatids fail to separate properly. How we see chromosomes with multiple copies. Non- disjunction occurs during anaphase II. Sister chromatids are not separated in to separate gametes.

Trisomy 21 characteristic facial features, short stature; heart defects susceptibility to respiratory disease, shorter lifespan prone to developing early Alzheimer's and leukemia. Often sterile, usually some degree of mental retardation.

Trisomy 13 serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months.

Trisomy 18 Almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.

Sex chromosome Non-disjunction Turner’s Syndrome

Cri du Chat 5p- syndrome Deletion of part of the 5 th chromosome. Intellectual disability, delayed development, small head size, low birth weight, low muscle tone. Infants have a cry that sounds like a distressed cat.

Which non- disjunction disorder is this?

Pedigrees

Pedigree- a diagram that traces a particular trait through generations.

Autosomal Recessive Affects males and females. Males and females can be carriers. Trait can skip a generation (s).

Autosomal Dominant traits- Men and women tend to be affected equally. There are no carriers or probability of carriers when genotypes are used.

Sex linked recessive trait Female carriers (or probability of female carriers if filling in genotype) Males are affected more often than females. (But females can be affected too!

Autosomal Recessive

Sex- linked recessive trait More males affected than females. Notice the females are not marked as carriers.

Autosomal Dominant Males and females affected equally Appears in every generation.