Non-Mendelian Genetics · Free PowerPoint Backgrounds Non-Mendelian Genetics Be sure to review Mendel’s 3 Laws!

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Non-Mendelian Genetics

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

• Barr Bodies

• Domestication

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: Red horses (RR) crossed with white horses (rr)

produce Rr roans that are “pink” in color.



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)

Often the controlling 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 carries the albino gene (c)

no matter what genes that organism has for color, the

organism will be albino.

B=black coat

c= albino

So a mouse with a

genotype of BBcc

will have NO

color!



Albinism



Albinism



Albinism



Albinism



Polygenic traits

Characterized by many genes are needed to affect a

single trait.

How would the alleles be written?

Ex: Eye color

EX: Hair color



Sex influenced

Genes that are expressed differently based on hormones

produced by the sex chromosomes X or y.

EX: patterned baldness-

Sexual dimporphism


http://en.wikipedia.org/wiki/Image:Male_pattern_baldness.jpg

http://en.wikipedia.org/wiki/Image:Male_pattern_baldness.jpg


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 genes carried on the X or Y

chromosomes.



• EX: Hemophilia

• XhXh or XhY= hemophilia.

• Gender specific heterozygosis



Why?

• X and y are not the same molecular mass/size

• Y chromosome has one job, change female default into male phenotype using hormones

• X carries over 1,000 genes

• y carries 78



Epigenetics

Phenotype that changes as genes are exposed

to external stimuli, like temperature.

Ex: Foxes or Siamese cats





Pleiotropy

One set of genes control multiple outcomes.

EX: White coat color & ability to hear. Or

fizzle-feather gene and egg production.





Barr Bodies• 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. Areas that are knocked out are called Barr bodies.

• Ex: calico cats





Domestication

• Human impacts on critical development results in phenotypic outcomes not seen in nature. Happens as sets of genes are controlled artificially. Ex: pie-balding, curled tail, droopy ears



Reduced penetrance

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

• EX: Reduced penetrance often occurs with familial cancer syndromes. For example, many people with a mutation in the BRCA1or BRCA2gene will develop cancer, but some people will not.

• Makes genetic predictors and treatment difficult.



Variable Expressivity

• Variable expressivity refers to the range of signs and symptoms that can occur in different people with the same genetic mutation.

• EX: 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).



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





• Which map would be used to show a

purebred dog’s ancestry?

• Which map would be used to show that a

non-disjunction has occurred in a human?

• Which map would be used to tell a person

that they have the gene for a specific

disorder.

• Be sure you know WHY, be ready to share

your answer


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Non-Mendelian Genetics · Free PowerPoint Backgrounds Non-Mendelian Genetics Be sure to review Mendel’s 3 Laws!