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Monday, February 25, 2013. Take a penny lab and staple it Take a “ How to Solve a Basic…. ” handout Turn in Meiosis Lab onto Computer cart. Genotype Phenotype Homozygous Heterozygous Allele. Gregor Mendel : ‘ father ’ of modern genetics.

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monday february 25 2013
Monday, February 25, 2013
  • Take a penny lab and staple it
  • Take a “How to Solve a Basic….” handout
  • Turn in Meiosis Lab onto Computer cart


  • Phenotype
  • Homozygous
  • Heterozygous
  • Allele
gregor mendel father of modern genetics
Gregor Mendel: ‘father’ of modern genetics
  • Why did Mendel use pea plants for his experiments?
  • Easy access and availability
  • Plants Exist in many varieties; have > heritable traits
  • Able to control reproduction of peas: self vs. cross pollination
  • Choose characters (traits) that exist in 2 distinct forms
  • Start experiments with true (pure) breeding [homozygous] lines of plants for a character/trait
  • Document parental cross & results of ALL offspring
  • Able to perform lots of trials in short time; obtain >> offspring
mendel s results and conclusions laws
Mendel’s Results and Conclusions (laws)
  • There are alternate versions of a trait (gene) = allele
  • Alleles are at the same locus on homologous Chromosomes
  • Offspring receive 2 alleles of each trait: one from each parent
  • Homologous Chromosomes ‘re-pair’ when gametes combine to form zygotes
  • Each allele (on homologous Xome) separates during gamete formation: Law of Segregation (Law of meiosis)

If alleles for a trait are different (Rr) then 50% chance of gametes (1/2) receive one allele (R) & 50% receive the other allele (r)

  • If alleles are different: Rr, then one allele ‘R’ is fully expressed as phenotype & other allele ‘r’ has no phenotypic effect =Law of Dominance
law of independent assortment
Law of Independent Assortment
  • If two or more traits are present in a genotype: AaBbDdEE

it can be assumed (unless otherwise stated) that each allele (letter) is on a separate chromosome

-->So how many chromosomes are represented by the genotype above?

-->How many possible gametes are created from the genotype above? (HINT: each trait is on a separate chromosome so apply law of independent assortment!)

--> How many possible offspring genotypes exist if both parents have the genotype above?

mendel and genetics problem vocabulary
Mendel and Genetics Problem Vocabulary
  • Generations: P1, F1, P2, F2
  • Gene, Allele, Trait
  • Dominant allele, recessive allele
  • Homozygous, Heterozygous
  • Genotype, Phenotype
  • Genotypic Ratio, Phenotypic Ratio
  • Test Cross
  • Hybrids: Monohybrid, Dihybrid, Trihybrid
mendel and genetics problem vocabulary1
Mendel and Genetics Problem Vocabulary

Trait = Seed shape

Phenotypes: Round seeds or Wrinkled seeds

Genotypes: = AA, Aa, aa

Homozygous = AA or aa

Homozygous Dominant = AA

Homozygous Recessive = aa

Heterozygous (hybrid) = Aa

Genotypic Ratio: 1AA : 2 Aa : 1aa

Phenotypic Ratio: 3 Round : 1 Wrinkled

probability rules
Probability Rules

Probability = chance event will occur

total # of possible events

“AND” Rule: Rule of Multiplication

For two or more separate events occurring at the same time (or in succession), multiply the individual probabilities of events together

EX 1: If parents are BB and Bb, what is chance of B gamete & b gamete combining to form zygote?

1/1 B and 1/2 b = 1/1 * 1/2 = 1/2 chance of Bb zygote

EX 2: Parent genotype is AaBBDdEe:

What is probability of gamete with genotype of ABdE?

1/2 * 1* 1/2 * 1/2 = 1/8 chance of ABdE

probability rules1














Probability Rules

“OR” Rule: Rule of Addition

To determine the chance one event OR another will occur, ADD the individual probabilities of each event

EX 1: If both parents are Tt, what is chance offspring will also be Tt?



pedigrees family tree p 260 fig 14 14

Pedigrees (family tree)p. 260 & fig 14.14

A pedigree is a family history showing inheritance of a particular trait through familial generations

karyotypes figure 13 3 p 237

Karyotypes (figure 13.3, p. 237)

Karyotypes are photographs of stained, human chromosomes present at metaphase of mitosis. Karyotypes are used to determine if chromosomes are defective and help to diagnose chromosomal disorders such as Down’s Syndrome.

karyotype of down s syndrome individual
Karyotype of Down’s Syndrome Individual



is also




Is this a boy or girl’s karyotype?

how does trisomy occur

Non-disjunction of either homologous chromosomes during meiosis I

How does trisomy occur?

Non-disjunction of sister chromatids during meiosis II