monday, february 25, 2013
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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 geneticsWhy 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)• 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• If two or more traits are present in a genotype:
AaBbDdEEit 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
• 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 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 = 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 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?
+T t OR +t T
14
14++ = 2
4
Pedigrees (family tree) p. 260 & fig 14.14A pedigree is a family history showing inheritance of a particular trait through familial generations
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 Normal Female
Karyotype of Down’s Syndrome Individual
Down’s
Syndrome
is also
called
Trisomy
21.
Is this a boy or girl’s
karyotype?
How does trisomy occur?Non-disjunction of either homologous chromosomes during meiosis I
Non-disjunction of sister chromatids during meiosis II
Some gametes exhibit trisomy (n+1) while others exhibit monosomy (n-1)?
Some gametes exhibit trisomy
(n+1) while others exhibit
monosomy (n-1)?