Genetics
Father of genetics
Gregor Mendel
What did Mendel know?
What did Mendel do?
Trait
Heritable trait / BASIC GENETICS REVIEW
·  study of heredity (inheritance of traits).
·  Austrian monk born in 1822.
ü  high school teacher and gardener.
ü  studied inheritance in garden pea plants.
·  flowers have male and female parts.
ü  produce pollen and egg cells.
ü  fertilization: male and female sex cells join
to form new cell
ü  peas are self-pollinating.
§  true-breeds: produce offspring like
themselves when s-p.
·  crossed true-bred peas: fertilized one plant with pollen from another.
ü  hybrids: offspring (F1) of crosses between
parents (P) with different traits.
·  true-bred short male(tt) X true-bred tall mom(TT)
ü  hybrid offspring = Tt
·  specific characteristic varies betw/ individuals.
·  trait that can be passed on to offspring.
What did Mendel conclude?
Principle of dominance
What did Mendel do next?
Law of Segregation / ·  factors that control traits are passed from generation to generation.
ü  genes: chemical factors that determine traits
ü  alleles: contrasting forms of a gene.
§  e.g. gene for “tallness” or “shortness”
·  some alleles are dominant; some are recessive.
ü  dominant allele: if present this trait is seen.
ü  recessive allele: seen if dominant allele is
not present.
ü  e.g. trait = plant height
tt = short plant
Tt or TT = tall plant
·  crossed hybrid pea plants (Tt X Tt)
ü  recessive trait not seen in F1.
ü  recessive trait seen in F2!
·  alleles separate when gametes (sex cells) are formed (during meiosis).
·  SO…..4 possible combinations of gametes during fertilization
Probability
Genetics?
Punnett Square
Vocabulary
Monohybrid cross
example
/ Genetics and Probability
·  likelihood that a particular event will occur.
ü  each toss is separate: heads = ½ each toss.
·  probability can be used to predict outcomes of genetic crosses.
ü  predictions are averages not absolutes
ü  larger sample sizes closer to predictions.
·  diagram used to record possible gene combinations from genetic crosses.
genotype: genetic makeup: write out alleles:“3Tt: 1tt”
phenotype: physical characteristics: “3 tall: 1 short”
homozygous: 2 identical alleles for a trait: TT or tt
heterozygous: 2 different alleles for a trait: Tt
·  cross 2 heterozygous tall plants (Tt x Tt)
ü  Offspring genotypes:
Ø  ¼ homozygous tall (TT);
Ø  2/4 heterozygous tall (Tt);
Ø  ¼ homozygous short (tt)
ü  offspring phenotypes: ¾ tall; ¼ short
Dihybrid cross
Example
Parents (P)
Filial (F1)
2nd generation (F2)
Principle of Independent Assortment
Summary of Mendel’s Principles / ·  cross true-bred pea plants with 2 traits
ü  dominant: round(R); yellow(Y)
ü  recessive: wrinkled (r); green (y)
·  RRYY (round/yellow) X rryy(wrinkled/green)
ü  offspring: RrYy (hybrid)
·  cross 2 F1 plants RrYy X RrYy
ü  possible gametes (FOIL): RY, Ry, rY, ry
·  genes for different traits segregate (separate) independently during formation of gametes.
ü  creates variation in offspring.
1.  Inheritance determined by genes passed from parents to offspring.
2.  Alleles of genes can be are dominant or recessive.
3.  Somatic cells have 2 copies of each gene (1 from mom; 1 from dad).
4.  Genes segregate independently of each other (RrYy) = RY, Ry, rY, ry.
Incomplete Dominance
Example
Codominance
Example
Multiple Alleles
Example
Blood type
Example

Sex linked genes
Example
Polygenic Traits
Epigenetics
(epi = above) / OTHER PATTERNS OF INHERITANCE
It’s not always so simple……
·  no allele is completely dominant.
ü  heterozygote is blend of 2 homozygous phenotypes.
·  red carnation X white carnation = pink carnation.

P genotype: ___X___
F1 genotype: ______phenotype: ______
·  both alleles dominant: both show up in phenotype of offspring.
·  red cow X white cow = roan cow (red and white).

P genotype: ___X___
F1 genotype: ______phenotype: ______
·  more than 2 forms of a gene
ü  more than one allele is dominant.
ü  more than 2 phenotypes in population.
·  alleles: dominant = A B; recessive = O
genotype / phenotype
AA / A
AO / A
BB / B
BO / B
AB / AB*
OO / O*
possible blood types
P phenotype: ____X____
F1 genotype: ______
F1 phenotype: ______
·  Gene located on X or Y chromosome (more commonly X…the Y chromosome is tiny)
1.  Colorblindness (recessive gene) located on X chromosome
ü  possible genotypes: XC Xc , XCXC, XcXc, XCY, XcY
ü  to be colorblind females need XcXc, males only need XcY
P genotype: ____X_____
F1 genotype: ______F1 phenotype: ______
2.  Hemophilia carried on X chromosome
ü  possible genotypes:XH Xh, XHXH, XhXh, XHY, XhY
P genotype: ____X_____
F1 genotype: ______F1 phenotype: ______
·  traits controlled by 2 or more genes.
ü  human skin color, eye color, height.
ü  AABBCCDD X aabbccdd…..many combinations.
ü  MANY intermediate phenotypes possible
·  traits determined by interaction of genes and environment.
ü  Genes are the PLAN.
ü  ENVIRONMENT determines how plan unfolds.
·  smoking, diet, stress, prenatal nutrition, trauma, etc. can affect which genes are turned on or off.
ü  chemical “tags” on DNA or change in histones.
ü  may be inherited over multiple generations.
ü  can change over a lifetime.
Mitosis Review

Meiosis
WHY? / MEIOSIS
·  1 cell division results in 2 genetically identical daughter cells
ü  makes cells for growth, repair, asexual reproduction
ü  occurs in somatic (body) cells
ü  starts and results in diploid cells (2n)
Ø  2 sets of homologous chromosomes
Ø  1 set from mom; 1 set from dad

·  2 cell divisions results in 4 daughter cells with ½ the number of chromosomes
ü  makes gametes (sex cells)
ü  occurs in sex organs of animals, plants, fungi, etc.
ü  starts with diploid cell (2n)
ü  results in 4 haploid cells (n)

Chromosomes
Crossing over
Gene Linkage and Mapping /
·  different number for each species.
·  humans: 2N = 46; 1N = 23
·  dog: 2N = 78; 1N = 39
·  shrimp: 2N = 254; 1N = 127
·  pineapple: 2N = 50; 1N = 25
·  homologous chromosomes exchange parts during Prophase I of meiosis
·  increases genetic variation

·  genes can be mapped to specific locations on chromosomes.
ü  figured out with fruit flies.
Ø  linked traits are on the same chromosome.
ü  linked genes not always inherited together
Ø  chromosomes cross-over during meiosis
ü  linkage maps show relative location of genes
Ø  lower cross-over frequency = closer
·  cross-over frequencies: A-B=8% B-C=10% C-A=2%