Non-Mendelian Genetics and Gene Mapping...•XhXh or XhY= hemophilia. •Gender specific...

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Non-Mendelian Genetics

and Gene Mapping

Be sure to review Mendel’s 3 Laws!

http://www.powerpoint-2010.com/


Today, we know that genes often do not

follow Mendel’s Laws all the time! There are

exceptions…..

• Incomplete dominance

• Co-dominance

• Epistasis

• Polygenics

• Sex influenced

• Sex linkage

• Epigenetics

• Pleiotropy

• X-Inactivation

• Reduced Penetrance & Variable Expressivity



Incomplete dominance

• Characterized by a blending of traits. Phenotype of

offspring falls somewhere between each parent, when

genotype is heterozygotic. These intermediate

offspring are called roans.

• EX: Wavy hair is the product of sharing alleles for curly

and straight hair. Or roan horses that appear “pinkish”



Co-dominance

• Characterized by the

expression of both

alleles. Shared

dominance. Even the

recessive allele affects

the organism.



EX: Blood type - A

and B are both

dominant!

• IAIA or IAi= A type

• IAIB = AB type

• IBIB or IBi = B type

• ii = O type

• Marker proteins

on cell membrane



Epistasis

• Characterized where one set of genes (2 alleles) controls a totally separate set of genes (2 other alleles)

at an entirely different loci on a different chromosome.

• One set of alleles block expression of the other alleles. Can results in general conditions called Somatic mosaicism, Ex: Heterochromia iridum Or can result in full blocking of entire gene sequence Ex: albinism



Epistasis

Ex: Albinism. If an organisms has the albino gene set (cc)

no matter what genes for pigmentation that organism

has for coat color, the organism will be albino.

B=black coat

c= albinoSo a mouse with a

genotype of BBcc

will have NO

color!



Albinism



Polygenic traits

Characterized by the need for multiple alleles

(genes) for the expression of a single trait.

Ex: Eye color

EX: Hair color



Sex influenced

Genes that are expressed differently based on hormones

produced by the sex chromosome combinations XX or

Xy. (testosterone/estrogen levels) Results in sexual

dimorphism

EX: patterned baldness or horn/antler development



X and y sizing

Y chromosome has one job, change female default into male phenotypeX carries over 1,000 genesy carries 78



Sex linkage

• If the genes are on the

y, they are called

holandric. Ex: Ear hair

• Those carried on the X

are more abundant

• EX: Muscular Dystrophy

Characterized by alleles (genes) physically located

on the X or y chromosomes.



• EX: Hemophilia

• XhXh or XhY= hemophilia.

• Gender specific heterozygocity



Ex: Red/Green

Colorblindness



Epigenetics

Characterized by phenotypic changes in

expression as those genes are exposed to

external stimuli.

Examples:



Domestication

• Human impacts on critical development results in epigenetic outcomes not seen in nature: Ex: pie-balding, curled tail, droopy ears



Stress and other factors?

• Ghost in your genes???



Pleiotropy

Characterized when one set of genes control

multiple outcomes.

EX: White coat color & ability to hear. Or

fizzle-feather gene and egg production.



X-Inactivation• Since females have 2 X chromosomes, if each

carries a regular dominant genes there could be a conflict in expression.

• So one set of genes is chemically blocked through a process called methylation to prevent conflict of expression.

• Ex: calico cats



Gene regulation in complex eukaryotes



Reduced penetrance

• Refers to the proportion of people with a particular genetic change (such as a mutation in a specific gene) who exhibit signs and symptoms of a genetic disorder.

• If some people with the mutation do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.

• Reduced penetrance often occurs with familial cancer syndromes. For example, many people with a mutation in the BRCA1 or BRCA2 gene will develop cancer, but some people will not.

• Makes genetic predictors and treatment difficult.

http://www.powerpoint-2010.com/http://ghr.nlm.nih.gov/gene/BRCA1http://ghr.nlm.nih.gov/gene/BRCA2


Variable Expressivity

• Although some genetic disorders exhibit little variation, most have signs and symptoms that differ among affected individuals. Variable expressivity refers to the range of signs and symptoms that can occur in different people with the same genetic mutation.

• For example, the features of Marfan syndrome vary widely— some people have only mild symptoms while others experience life-threatening complications even though all affected people with this disorder have a mutation in the same gene (FBN1).

• As with reduced penetrance, variable expressivity is probably caused by a combination of genetic, environmental, and lifestyle factors, most of which have not been identified.

http://www.powerpoint-2010.com/http://ghr.nlm.nih.gov/condition/marfan-syndromehttp://ghr.nlm.nih.gov/gene/FBN1


Gene mapping

There are 3 main types of gene maps based on the details

the “map” illustrates

A) Pedigree

B) Karyotype

C) Cytological

Gene maps are used to track and predict genetic traits and disorders.



Pedigree Maps are used to illustrate a known

phenotype through families. They do not illustrate

chromosomes or gene sequences.

Circles=Female, Squares=Males



Karyotype, or Chromosomal Map, shows

the overall large chromosome structure, but

not gene sequence details-Autosomal versus

sex chromosomes



Cytological maps - illustrate actual gene

sequences of the DNA


Non-Mendelian Genetics and Gene Mapping...•XhXh or XhY= hemophilia. •Gender specific...

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