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
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