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Genetics

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Genetics & Inheritance

What you get isn’t always what you see

Intro to Inheritance

What is Heredity?

http://learn.genetics.utah.edu/content/inheritance/intro/

What is a Trait?

http://learn.genetics.utah.edu/content/inheritance/traits/

http://learn.genetics.utah.edu/content/begin/t

our/inheritance.swf4/22/20152/3/03 10:39 AM

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Gregor Mendel (7/22/1822 - 1/6/1884)

“Father of Modern Genetics” Born in on July 22, 1822 in

Heinzendorf Moravia in what is now

the Czech Republic Was Heinzendorf,

Austria.

He died in Brno, Austria January 6,

1884

Augustinian monk employed as high

school natural science teacher for 20

years

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Gregor Mendel (7/22/1822 - 1884)

Experimented with garden peas Pisumsativum

Tested some 28,000 pea plants in 7 years

Used artificial fertilization

Worked in limited space in monastery garden

First to consider single traits of hybridization experiments results

Devised precise mathematical pattern

Did not understand biological process, eg. chromosomes & DNA

1900 three botanists “discovered” his papers while researching their own findings

Mendel, O.S.A., experimental garden (35x7 meters) in the grounds of the

Augustinian Monastery in Old Brno.Its appearance before 1922.

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Mendel’s Pea Plants

Scientific name: Pisum sativum Diploid

Seven pairs of traits

• Axial / terminal flowers (Aa)

• Purple / white Flower coats (Pp)

• Tall / short (Tt)

• Round / wrinkled (Ss)

• Green / yellow seeds (Gg)

• Inflated / constricted (Ii)

• Green / yellow unripe pods (Gg)

Mendel’s

Pea Plants

Pisum sativum

Mendel fertilized the pea flowers and removed other underdeveloped reproduction parts before self-fertilization could take place.

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William Bateson, English

Gave name genetics

based on Greek term

"to generate"

Promoted Mendell's

view of paired genes

using term allelomorph,

shortened to allele.

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Basic Ideas

Mendel used term unit characters based on physical elements and occurring in pairs of allele. We now call these genes.

The paired genes (allele pairs) separate form one another and are distributed to different sex cells through meiosis

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Mendel's 3 Laws

1. The Law of Dominance

In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.

Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.

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Mendel's 3 Laws

2. The Law of Segregation

During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.

Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

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Mendel's 3 Laws

3. The Law of Independent Assortment

Alleles for differenttraits are distributed to sex cells (& offspring) independently of one another.

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Terms

Allele: an alternate form of a gene. Variants that occur at the same locus.

Homozygous: having the same alleles for same trait

Heterozygous: having different alleles for same trait

Phenotype — physical looks of genes (Yellow, Green)

Genotype — the actual genes (YY, Yy, yy)

Dominance — phenotypic recognition

Recessive —carriers

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Labeling:

The standard way of labeling the variation information of a trait in a particular organism is using two letters.

Capital letters represent information which is dominant.

Lowercase letters represent the recessive. The letter being used describes a variation (usually the recessive) of the trait.

YY

stands for a plant where both

pieces of color information are

dominant - yellow. The plant is

yellow.

Yy

stands for a plant where one

piece of color information is

dominant - yellow, and the

other is recessive - green. The

plant is yellow.

yystands for a plant where both

pieces of color information are

recessive - green. The plant is

green.

Pea Plant Traits

Trait:

Dominant

Expression:

Recessive

Expression:

1 Form of ripe seed Smooth Wrinkled

2Color of seed albumen

Yellow Green

3 Color of seed coat Grey White

4 Form of ripe pods Inflated Constricted

5 Color of unripe pods Green Yellow

6 Position of flowers Axial Terminal

7 Length of stem Tall Dwarf15

Examples of genetic traits studied by Mendel

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Examples of Phenotypes & Genotypes

Two trait

phenotypes for

garden peas

Two trait

genotypes for

garden peas

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Green Round GGRR GgRr

Yellow Round ggRR ggRr

Green Wrinkled GGrr Ggrr

Yellow Wrinkled Ggrr —

Terms

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Monohybrid Cross

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Punnett Square

Diagram of a Monohybrid

Cross

Y Y

y

y

Monohybrid Cross, P1

Genotype Phenotype

Gg Green

Homozygous Green X Homozygous Yellow

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Homozygous Yellow

Homozygous

Green

Offspring

Heterozygous Yellow

P1 Y Y

yYy Yy

yYy Yy

Monohybrid Cross, P

Genotype Phenotype

Gg Green

Homozygous Green X Homozygous Yellow

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Homozygous Yellow

Homozygous

Green

Offspring

Heterozygous Yellow

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Monohybrid Cross, ƒ1

Genotype Phenotype

GG Green

Gg Green

gg Yellow

Heterozygous Green

X

Heterozygous Green

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Monohybrid Ratios

Genotypic Ratio

1:2:1

Phenotypic Ratio

3:1

# Genotype Phenotype #

1 GG Green3

2 Gg Green

1 gg Yellow 1

Dihybrid Cross

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Dihybrid Cross

Use each letter only twice

G g R r

GR Gr gR gr

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

Genotypes

GGRR

GGRr

GgRR

GgRr

GGrr

ggRR

Ggrr

ggRr

ggrr

Genotypic Ratio

1:1:2:2:4:2:2:1:1

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

Phenotypes

Green Round

Green Wrinkled

Yellow Round

Yellow Wrinkled

Phenotypic Ratio

9:3:3:1

Dihybrid Ratios ƒ1 cross

Genotypic Ratio

1:1:2:2:4:2:2:1:1

Phenotypic Ratio

9:3:3:1

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Law of Probability

The chance of two

or more independent

events occurring

together is the

product of the

chances for their

separate

occurrences.

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Terms

Codominance

Heterozygote expressing

each allele equally

Semidominance

Similar to codominance,

but not equal expression

of both alleles

Filial

Latin for progeny

F1 --

F2 --

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Partial Dominance

When one allele isn't

fully dominant over its

partner

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Partial Dominance Example

Genotype Phenotype

RR Red

Rr Pink

rr White

Pink flowers

X

Pink flowers

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Epistiasis - two genes affecting property do not have

equal vote

Example:

Melanin and melanin deposition (black, white, and brown coat of guinea pig).

Black is dominant brown is recessive when melanin producing gene is present.

Coat is white when no melanin is deposited.

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Collaboration

Two genes interact to

produce a novel

phenotype

Example: comb types

in chickens

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Multiple Gene Inheritance (polygenic)

Nilsson-Ehle's trigenic

cross of wheat (10-8)

Frequency distribution

(10-9)

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Sex-related Characteristics

Holandric - genes

unique to Y

chromosome, hair

pinna on ears

Eye color in fruit flies

Hemophilia

Color blindness

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Sex-Linked Characteristics

A trait associated with a gene that is carried only by the male or female parent.

If a gene is found only on the X chromosome and not the Y chromosome, it is said to be a sex-linked trait.

Because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to the gender of the individual.

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Sex-linked Inheritance

Drosophila

Fruit Flies

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Sex-linked Inheritance

Hemophilia

Rare disorder in which blood doesn't clot normally because it lacks sufficient blood-clotting proteins (clotting factors).

20K to 200K US cases per year

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Sex-linked Inheritance

Color Blindness

There is no actual blindness but there is a deficiency of color vision.

Will be expressed in males with a higher probability than in females because males only have one X chromosome

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Pedigree

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Slugs Mating

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Webpage Links The Genetic Code - S.D. Black, U. of Texas Health Center at Tyler Table relating nucleic acid

triplet to the corresponding amino acid.

Molecular Biology - The Biology Project, Biology, University of Arizona Activities, Problems sets, and Tutorials: Molecular Genetics; Nucleic Acids; Recombinant DNA Technology; Eukaryotic Gene Expression

Prokaryotic Genetics and Gene Expression from the MIT Hypertextbook - M.I.T. Tools for studying prokaryotic genetics, biochemical genetics, Lac operation, etc.

The making of the nucleosome - D. Pruss Simplified images and a tour.

http://www.agen.ufl.edu/~chyn/age2062/lect/lect_10/lect_10.htm

http://www.borg.com/~lubehawk/mendel.htm

http://www.sonic.net/~nbs/projects/anthro201/disc/