Introduction to Genetics

Genetic variation within the White-cheeked Rosella

Heredity & Genetics

1. Heredity: The passing of traits from parents to offspring

2. Genetics: Study of heredity

3. Inherited characteristics are called traits

Gregor Mendel was the first person to predict how traits are transferred.

Austrian monk who studied garden peas

Mendel used peas because-they Reproduce sexually - gametes in the same

flower- Fertilization could be

controlled

http://www2.edc.org/weblabs/WebLabDirectory1.html

-Mendel transferred pollen from plant to plant and then studied resulting peas

-Studied only one trait at a time

- Mendel is called the “father of genetics”

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

Section 11-1

Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants

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Phenotypes & Genotypes

Phenotype: appearance of an organismExample: short, tall, green, yellow

Genotype: gene combination of an organismExample: tt, TT, Tt, gg, GG, Gg

Heterozygous: the 2 alleles are differentExample: Tt -heterozygous

Homozygous: the 2 alleles are the sameExample: TT means homozygous dominant, and tt means homozygous recessiveLivestock: http://www.parkelivestock.com/semensales.htm

http://www.mcrobertsgamefarm.com/buffalo/white_buffalo.htm

Heterozygous & Homozygous

Traits can be dominant or recessive

Dominant traits: exhibited trait, written with 1 or 2 capital letters

Example: T

Recessive traits: inhibited trait, written with recessive

letters(lowercase letters)Example: t

Monohybrid CrossesCrosses that differ by a single trait

Example: Tall pea plant x short pea plant

The first generation produced offspring resembling only one parent

Example: all tall pea plants

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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The second generation produced:3/4 of peas were tall1/4 of peas were short

Mendel concluded that each trait has 2 factors

Factors are now called alleles

Inherit one allele from mother and one allele from

father

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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Section 11-2

Tt X Tt Cross

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Section 11-2

Tt X Tt Cross

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Probability: the chance or percentage of chance of a trait being exhibited

Mendel Revisited

• Quick Review

– Genotype: genetic code for traits TT Tt tt– Phenotype: physical appearance– Homozygous, heterozygous, dominant, recessive

• Punnett Square:– TT x tt– Tt x Tt

Mendel’s Laws• 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. TT (tall) x tt (short) all Tall

• 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. Tt (tall) x Tt (tall) alleles act independently

75% Tall 25% short

Incomplete dominance Incomplete dominance-neither allele is Dominant or recessive Example- white flowers X red flowers= pink flowers

-a mixture or blend of the parent colors

Codominanceoffspring shows phenotype of neither parent both alleles are dominant Example- bay horse x white horsed= roan horse- both hair colors are present

Multiple and Sex-linked AllelesMultiple alleles: more than 2 alleles control a trait

Example-blood type in humansa. blood type is determined

by presence or absence of proteins on the surface

of red blood cellsExamples- A, B, AB, & O

Genotype PhenotypeAA, Ao A blood

BB, Bo B blood

OO O blood

To determine the blood types of possible offspring

Parents = A blood, O bloodGenotypes AA, AO OO

Calico Cats

• Calico is not a breed of cat, but an unusual coloring occurring across many breeds

• Virtually all calico cats are female– a male calico is a genetic anomaly and usually

sterile – Producing calico kittens through selective breeding

also is nearly impossible due to unpredictable actions of genes and chromosomes when cells multiply in a feline fetus

Sex linked alleles: controlled by genes located on sex chromosomes

-usually carried on the X chromosomes

-Females XX, males XY-If trait is X-linked, males pass

the trait on to all their daughters, but none to their sons

-mothers have 50/50 chance of passing it to all their children

Examples-colorblindness

Colorblindness,Hemophilia, MD

• Colorblindness – recessive disorder where a person can’t distinguish between certain colors.

• Hemophilia – blood clotting disorder• Muscular Dystrophy – deterioration of the

skeletal muscle. Children rarely live past early adulthood.

Colorblindness test

• http://www.geocities.com/Heartland/8833/coloreye.html

Aneuploidy

• Abnormal # of chromosomes • Trisomy – aneuploidy of the 1st 22 pairs of

chromosomes– Autosomes – 1st 22 pairs of chromosomes.

• Turners Syndrome – XO 1/2000. Females that lack ovaries, shorter, and live normal lives.

• Klienfelters syndrome – 1/500 males XXY taller than avg., longer limbs, sterile

Karyotype

• A chart of all 23 pairs of chromosomes– Tell the sex of the child– Aneuploidy yes/no

Significance of cell reproduction

Unicellular Organisms: reproduce by cell division, this is also called binary fission.

Multicellular organisms- growth and repair upon cell division, also the

production of sex cells.

Chromosomes

-Carriers of genetic material found in nucleus-Made up of DNA-Information is copied and passed to future generations

Usually exist as chromatin-long, winding strands which condense into chromosomes before dividing Humans have 46 chromosomes in body cells, 23 in sex cells

MeiosisMeiosis

• Similar in many ways to mitosisSimilar in many ways to mitosis• Several differencesSeveral differences• Involves 2 cell divisionsInvolves 2 cell divisions• Results in 4 cells with 1/2 the normal genetic Results in 4 cells with 1/2 the normal genetic

information information

VocabularyVocabulary

• Diploid (2N)Diploid (2N) - Normal amount - Normal amount of genetic materialof genetic material

• Haploid (N)Haploid (N) - 1/2 the genetic - 1/2 the genetic material.material.

• Meiosis results in the formation Meiosis results in the formation of haploid cells.of haploid cells.

• In Humans, these are the In Humans, these are the OvaOva (egg) and (egg) and spermsperm..

• Ova are produced in the Ova are produced in the ovariesovaries in femalesin females

• Process is called oProcess is called oogenesisogenesis• Sperm are produced in the Sperm are produced in the testestestes

of males.of males.• Process is called Process is called

spermatogenesisspermatogenesis

Meiosis Phases

• Meiosis occurs in 2 phases; Meiosis I, & Meiosis II.

• Meiosis I.– Prior to division,

amount of DNA doubles

Crossing OverCrossing Over

• During metaphase 1 During metaphase 1 homologous homologous chromosomes line-up chromosomes line-up along the metaphase along the metaphase plateplate

• Areas of homologous Areas of homologous chromosomes connect chromosomes connect at areas called at areas called chiasmatachiasmata

Crossing over contd.Crossing over contd.

• Crossing OverCrossing Over of genes of genes occurs now occurs now – Segments of homologous Segments of homologous

chromosomes break and chromosomes break and reform at similar locations.reform at similar locations.

– Results in new genetic Results in new genetic combinations of offspring.combinations of offspring.

– This is the main This is the main advantage of sexual advantage of sexual reproductionreproduction

Chromosome reductionChromosome reduction

• During anaphase 1, During anaphase 1, each homologous each homologous chromosome is chromosome is pulled to opposite pulled to opposite sides of the cell. sides of the cell. Unlike mitosis, Unlike mitosis, THE THE CENTROMERES CENTROMERES DO NOT BREAKDO NOT BREAK..

Meiosis I continuedMeiosis I continued

• Nuclei may or Nuclei may or may not reform may not reform following following division.division.

• Cytokenesis may Cytokenesis may or may not occur or may not occur

Meiosis II• DNA does not double• Chromosomes randomly

line-up along metaphase plate like regular mitosis.

• During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell.

• Nuclei reform and cytokenesis usually occurs (although it is often unequal).

Overview of MeiosisOverview of Meiosis

Comparison of Mitosis & MeiosisComparison of Mitosis & Meiosis