1. Mendelian Genetics

2. VOCABULARY Genetics: _______________________________
Heredity: the passing on of characteristics (traits) from parents to offspring
Genes: chemical factors that determine traits
located on chromosomes, they control how an organism develops
Alleles: different forms of the same gene (AA,Aa,aa)
Traits: specific characteristics that varies from one individual to another; EX: seed color and height
_______________: the uniting of male and female gametes (sperm and egg)
Cross: combining gametes from parents with different traits

3. ___________________ + = + = Male Zygote Female Zygote
Autosome: chromosomes that are not sex chromosomes + =
22 + Y
22 + X
44 + XY
Male Zygote + =
22 + X
22 + X
44 + XX
Female Zygote

4. Gregor Mendel
Mendel (1822): crossed pea plants to study the inheritance of traits.
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Why did Mendel use pea plants?
They reproduce sexually
They have two distinct, male and female, sex cells called gametes
Their traits are easily to isolate

5. Mendel Cont.
Mendel crossed (fertilized) the pea plants and studied the results
Mendel concluded 2 things:
Inheritance is determined by factors that are passed from one generation to the next
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6. Phenotype and Genotype
Phenotype: They way an organism looks
EX: red hair, brown hair, short, tall
Genotype: the gene combination of an organism
EX: AA or Aa or aa

7. Principle of Dominance
Dominant Trait: the trait that is expressed
traits always appear; uppercase letter (A)
Recessive Trait: the trait that is unexpressed
traits that dissappear; lowercase letter (a)
for a recessive trait to appear, both parents must give the recessive allele
Homozygous: The two alleles for a trait is the same; EX: (AA or aa)
Heterozygous: The two alleles for a trait is different; EX: (Aa)

8. Solving Crosses ____________ = A (AA or Aa) Recessive = a (aa)
Solve crosses using Punnett Square
Punnett Square: diagram used to determine the probability of an offspring having a particular genotype
Does not show what
the offspring will be.
Answer questions based on results from the Punnett Square
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9. Monohybrid Crosses Monohybrid Cross: Cross that involves one pair
of contrasting traits. Ex: hair color
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Sample problems: Red hair (R)is dominant to white hair (r)
RR x rr → red hair x white hair
Rr x rr → red hair x white hair
Rr x Rr → red hair x red hair
Rr x RR → red hair x red hair

10. Sample Problems R r 1. R R 2. r r Rr Rr r r Rr Rr 4. R r R r 3. R R R
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_________ r r Rr Rr
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_______ r r Rr Rr
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_______ 4. R r R r 3.
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_________ R R
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_______ R r
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11. Sample Question
Short hair (L) is dominant to long hair (l) in mice. What is the genotype and phenotype ratio of a heterozygous short-haired mouse crossed with a long-haired mouse?

12. Sample Answer
Short hair = dominant = L (LL or Ll) long hair = recssive = l (ll)
Ll x ll (heterozygote parent = Ll)
Punnett Square:
Genotype ratio: _______________________
Phenotype ratio: ______________________
Ll x ll L l