What is the probability of rolling a 1 and 5 in two separate rolls? Agenda for Tuesday March 30 th...
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Transcript of What is the probability of rolling a 1 and 5 in two separate rolls? Agenda for Tuesday March 30 th...
What is the probability of rolling a 1 and 5 in two separate rolls?
Agenda for Tuesday March 30th • Mendel notes• Punnett Squares
Law of Segregation
• Chromosomes separate during meiosis and unite during fertilization
Law of Independent Assortment
• Random distribution of chromosomes occurring during meiosis– Genes on separate chromosomes sort independently
The point?
• It’s all random– Which alleles we get (genes) (traits)– Crossing over– Etc.
What is a trait?
Agenda for Thursday March 31st 1.Mendel2.Punnett Squares
Mendel• Father of genetics• Loved nature• Austrian monk
– taught natural science – worked on plant breeding experiments
using pea plants
• Developed basic understanding of genetics and inheritance
Mendel’s Work
• It took him 2 years to select the pea plant• He collected data for 10 years.• His sample sizes were large; he tabulated
results from 28,000 pea plants.• He replicated his experiments.• Published work but was dismissed
– Found later
Mendel’s Experiment
• P Generation – parent generation• F1 generation – first filial generation, offspring
of parents• F2 generation – second filial generation,
offspring of F1 generation
• Ratio of 3:1
Mendel’s ResultsP1 F1 F2 F2 ratio
smooth X wrinkled seeds
all smooth 5474 smooth1850 wrinkled
2.96:1
yellow X green seeds
all yellow 6022 yellow2001 green
3.01:1
axial X terminal flowers
all axial 651 axial207 terminal
3.14:1
red X white flowers all red 705 red224 white
3.15:1
inflated X constricted pods
all inflated 882 inflated299 constricted
2.95:1
green X yellow pods all green 428 green152 yellow
2.82:1
tall X dwarf plants all tall 787 tall277 dwarf
2.84:1
Collected 6022 yellow and 2001 green3:1 ratio
Conclusions• 2 forms of seed traits in the pea plants
– Alleles – forms of a gene passed on to each generation• Green and yellow pea seeds
– We use letters to represents alleles/genes/traits
– Individuals are diploid so we use 2 letters
**Genes are on the chromosomes
Dominant and Recessive
• Dominant – the trait we see (expressed with capital letter, A)
• Recessive – trait that is masked (expressed with lower case letter, a)
• Which is better, dominant or recessive?
Dominance
• Mendel’s experiment, green color was masked– Recessive
• Organism with two of the same allele – homozygous– AA, aa
• Organism with two different alleles – heterozygous– Aa– Dominant trait observed (notice the dominant allele)
Homozygous (pure bred)
Same
HH hh
Heterozygous (hybrid)
Different
Hh Rr
Genotype
Allele makeup of an individual
Tt T T tt
RR Rr rr
PhenotypeObservable characteristics of an individual
Punnett Squares
Let’s Practice
PracticeA Tt (tall) plant is crossed with a tt (short plant).
What percentage of the offspring will be tall?
A green pea sead (gg) is crossed with a hybrid yellow seed (Gg). What will be the genotypic and phenotypic ratios of the offspring?
PracticeA heterozygous plant (Tt) is crossed with another
heterozygous (Tt) plant. What percentage of the offspring will be tall?
In guinea pigs, rough coats are dominant over smooth coats. If an Rr guinea pig is crossed with an Rr guinea pig. What are the chances of each genotype and phenotype? Include genotypic and phenotypic ratios.
Define homozygous, heterozygous, phenotype, and genotype
Agenda for Friday April 1st 1.Quiz2. More practice with Punnett Squares
A Tt (tall) plant is crossed with a tt (short plant). What percentage of
the offspring will be tall?
• Quiz• Review Punnett Squares• Making Dragons
Making Dragons
A Rr (round) seed is crossed with a Rr (round plant). What are the
phenotypic and genotypic ratios?• Finish making dragons• Comparing ratios of Punnett squares to actual
ratios lab
What is the process of combining two gametes called?
• Finish Comparing Punnett Square ratios• Dihybrid Crosses
Dihybrid Cross
• a cross between of two individuals that differ in two traits of particular interest
For example: GGbb/ggBb or RRYY/rryy
What is a dihybrid cross?
• Dihybrid Review• Gene Linkage and Polyploidy
– Mapping Chromosomes
Genetic Recombination
• New combination of genes produced by crossing over and independent assortment
Why is genetic recombination important?
Gene Linkage
• Genes on same chromosomes are said to be linked– Travel together during Meiosis
• Not always true – crossing over occurs
• Genes close together cross over more frequently– Make chromosome maps based on that info.
Chromosome Map
• Map genes A, B, C, D
• Frequency of crossing over– AD = 25%– AB = 30%– CD = 15%– BD = 5%– BC = 20%
Polyploidy
• Most cells are Diploid (2n)• Polyploidy – one or more extra sets of
chromosomes– Triploid – 3n
• In humans polyploidy is lethal– Other organisms it is not– Roughly 1 in 3 plants are polyploidy
• Increased vigor and size