Mendelian Inheritance and Exception and Extensions of

Mendelian Inheritance

Tay-Sachs Disease

Conner Died at 22 months

Mendel

Performed experiments with pea plants in late 1850’s early 1860’s

Created theories explaining dominance, segregation, and independent assortment

Work not really noticed until after death

Considered “Father” of genetics

Mendel’s Experiments

Studied seven _______ traits Seed form (Round and

wrinkled) Seed color (Yellow and green) Pod form (Smooth and

constricted) Pod color (Green and yellow) Flower Position (Axial and

terminal) Seed coat color (Gray and

white) Stem length (Tall and short)

Mendel’s Experiments (cont)

Mendel took a _____-breeding tall and ____-breeding short and cross-pollinated them (_____ generation)

Result ________ tall (F1 generation)Repeated with other traitsConclusion: one form of trait is _________ over the other Tall is dominant, short is ___________

Dominant vs Recessive

These refer to an action or abundance of ___________

Recessive is often “_____ of function” If causes disorder, can be severe and early-

onset

Dominant can be “_______ of function”

Mendel’s Experiments (cont)

Mendel self-pollinated the F1 generation

Result: ____ Tall, ___ short (F2 generation)

Repeated with other traits

Conclusion: Each plant has two copies of trait that ___________ from each other during gamete formation; gamete used is chosen at random

Trait Nomenclature

_________- form of a traitDominant allele given capital; recessive is same letter, lower case (T= tall and t=short)Genotype- ______________________ Homozygous- same two alleles

Homozygous dominant- two dominant (_________) Homozygous recessive- two recessive (_________)

Heterozygous- two different alleles (_______)

Phenotype- expressed trait Wild type- expression of most common form of the trait Mutant- expression of different form of trait resulting from

mutation

Punnett Square

Bookkeeping tool for genetic problems

Gamete possibilities for each parent on each side

Independent Assortment

Traits are independent of each other if on different ______________

Mendel got lucky Most of the seven traits used were on different

chromosomes

Dealing with Two Traits

__________ cross

Two trait Punnett Square

Still list all possible gametes on each side

What are the possible gametes for a parent who is TtRr?

Dihybrid Cross

Probability

Can be used to determine the outcome of inheritance

Probability of Simple Events

Probability of Independent Events

Probability of Dependent Events

Pedigree

Pictorial genealogy of a family showing the inheritance of a particular trait

Individuals are shown and connected using symbols on pg 88

Can be used Determine if trait is dominant or recessive Determine probable carriers within family Determine probability of inheritance for future

generations

Pedigree Analysis

Pedigree Analysis (cont)

Polydactyly

Beyond Mendelian Inheritance

Sometimes inheritance doesn’t seem to follow Mendel’s laws

Lethal Alleles

Sometimes the combination of two alleles is lethal (____________________)

If death is during development, expected Mendelian ratio is not observed

Multiple Alleles

Trait has more than _________ alleles

Human Blood Groups- ________ system Three alleles

IA (codes for an ___-type ID on blood cell) IB (codes for a ___-type ID on blood cell) i (codes for ____ ID on blood cell)

Incomplete Dominance

Heterozygotes express phenotype __________ two homozygous phenotypes

Snap dragon flowers RR= red Rr = ________ rr= white Pink is created because Rr plants don’t have as

much pigment as RR plants do

Codominance

Heterozygotes express _____________ within the phenotypeHuman Blood Groups IA IA- A blood (only A-type ID on blood cells) IA i- A blood (only A-type ID on blood cells) IB IB- B blood (only B-type ID on blood cells) IB i- B blood (only B-type ID on blood cells) ii- O blood (no ID on blood cells) IA IB- AB blood (both A-type and B-type ID on blood

cells)

Epistasis

One gene affects the __________ of another

Bombay phenotype- encodes for glycoprotein on red blood cell needed to attach the A-type or B-type ID

A person who is homozygous recessive for Bombay (____) will have ____ blood regardless of their ABO genotype

Penetrance

Percentage of how often a genotype is expressed into a phenotype

____________ penetrance- person with affected genotype always expresses the phenotype

____________ penetrance- person with affected genotype may not show the phenotype

Expressivity

Expresses the varying _________ of a phenotype being expressed

Pleiotropy

Occurs when an inherited gene causes many effects within the body

Can be difficult to trace because symptoms may vary from person to person

Phenocopy

___________________ creates symptoms that mimic a genetic phenotype

Genetic Heterogeneity

Different genes can create the same ________________

Mitochondrial DNA

Mitochondria contain a “mini-chromosome” with _______ genes

mtDNA mutes rapidly because there is no DNA repair and high exposure to free radicals

Only inherited from _________ (mother passes to ____ her children)

Genes code mostly for machinery for protein synthesis

Mitochondrial Disorders

Often affect most tissue with high amounts of mitochondria

Heteroplasmy- individual has mitochondria with normal genes and mitochondria with mutant genes

Creates a wide range of expressivity

Linkage

Linked genes are on the same ___________

Linked traits do not show independent assortment

Mixing of these traits can only occur during ______________

Linkage Nomenclature

_________ inheritance- inheritance of allele combination in parents without crossing-over__________ inheritance- inheritance of allele combination created during crossing-over_____ formation- person heterozygous for both traits has both dominant alleles on one homolog and both recessive alleles on the other______ formation- person heterozygous for both traits has one dominant and one recessive allele on each homolog

Linkage Map

Linkage results can be used to map out relative positions of genes on chromosomes

Distance between genes is measured in centimorgans (equal to the percentage of recombination occurring between the two)