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I. GeneticsA. Gregor Mendel

1. Known as the father of genetics.2. Worked with garden peas.3. Led to knowledge of inheritance.4. Heredity – transmission of traits from

parents to the offspring.B. Gene – the basic unit of inheritance.

1. Made of DNA.2. In sexual reproduction:

a) One gene from the male parent.b) One gene from the female parent.c) Why you have two copies of same

chromosome.

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3. Alleles – alternate forms of a gene.a)Ex: seed color (yellow, green seed)

C. Dominant and Recessive alleles1. Dominant alleles – an allele that masks

the presence of another allele.a)Always use capital letters.

2. Recessive alleles – an allele that is being masked by the dominant allele.a)Always use lower-case letters.

3. Homozygous – when both alleles are the same (homo = same).a)Homozygous Dominant (AA) or

homozygous recessive (aa)4. Heterozygous – when both alleles are

NOT the same (Hetero = different)a)Heterozygous dominant (Aa)

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5. Genotype – genetic makeup of an organism.a) Ex: AA, Aa, aab) Geno = genes, genetics

6. Phenotype – physical appearance of an organism.a) Ex: tall, yellow, wrinkledb) Pheno = physical

II. Mendel’s workA. Three Principles:

1. Principle of dominance – an allele masks another allele.

2. Principle of Segregation – two alleles for a characteristics separate during gamete formation.

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3. Principle of Independent Assortment – alleles for different characteristics (genes) are distributed to gametes independently.

III. Punnett Squares – used to describe the ratio of expected outcomes of a genetic cross.

A. Monohybrid cross – (mono meaning one) 1 trait is crossed.

1. Have two alleles for each gene.2. Ex: T = tall, dom

t = short

TT x tt (parents)

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3. More ex:TT x TtTt x Tt

4. Testcross – an individual with unknown genotype is crossed with a homozygous recessive individual.a)Ex: rabbit color B = black, dom

b = brown

BB x bb Bb x bb

• If any brown rabbits then the parents were heterozygous, if not then they were homozygous.

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5. Incomplete dominance – when one allele does not completely mask another.a)The organism shows a blend of the two.b)Ex: Japanese 4 o’clocks R = red

W = whiteRR x WW RW =

pink6. Codominance – when both alleles contribute

to the phenotype of the organism (no blending).a)Ex: cattle color R = red

r = whiteRR x Rr Rr =

roan7. Polygenic traits – traits controlled by two

or more genes. (poly = many)

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8. Sex-linked traits – trait occurs only on a sex chromosome.a)Ex: colorblindness XX =

femaleB = normal, dom

XY = maleb = colorblindness

XBXB = normal femaleXBXb = normal female, carrierXbXb = colorblind femaleXBY = normal maleXbY = colorblind male

XBXb x XBY

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9. Blood types:a)A blood = IAIA or IAib)B blood = IBIB or IBic)AB blood = IAIB d)O blood = ii

B. Dihybrid Crosses – two genes are crossed at the same time.1. Ex: seed color and textureP = purple kernel, domP = yellow kernel, recS = smooth, domS = wrinkled

PpSs x PpSs (remember Foil – for all possible combinations of gametes)