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Bell Ringer: (5 min.). Section 11-3: Exploring Mendelian Genetics. Independent Assortment. Mendel wanted to know: Does the segregation of one pair of alleles affect that of another? For example: Does the allele for seed color effect the shape of the seed? - PowerPoint PPT PresentationTRANSCRIPT
Bell Ringer: (5 min.)
Section 11-3: Exploring Mendelian Genetics
Independent Assortment
• Mendel wanted to know:– Does the segregation of one pair of alleles affect
that of another?• For example: Does the allele for seed color effect the
shape of the seed?
• 1. To find this Mendel created a two factor cross and followed two different genes as they passed from one generation to the next.
The Two Factor Cross: F1
• Crossed true breeding plants for round (RR) yellow (YY)peas– 2. Genotype (RRYY)
• With true breeding plants for wrinkled (rr) green (yy) peas– 2. Genotype (rryy)
• And proceeded to observe the offspring
The Two Factor Cross: F1
ry ry ry ry
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
The F1 Results:
• 3. This shows that the dominant alleles are present:– Phenotype:
• Heterozygous• Round Yellow Seeds
– Genotype:• RrYy
• 4. Does this result show if genes segregate independently?– Nope
The Two Factor Cross: F2
• 5. Mendel took the F1 generation (heterozygous) and crossed them.
• He wanted to see if the two traits would separate independently of one another or if dominant would stick with dominant and recessive stay with recessive.
• Was very curious of the possible outcomes.
10. The Two Factor Cross: F2RY Ry rY ry
RY
Ry
rY
ry
The F2 Results:
• 6. & 8. There was a total of 556 seeds produced:– Round Yellow: 315– Round Green: 105– Wrinkled Yellow: 104– Wrinkled Green: 32– 7. There were seeds that displayed combinations not
found in the parents (RRYY and rryy)• Did Independent assortment occur?– YES!
Let’s Look at the Numbers Again:
• 9. Count up the Phenotypes, what is the ratio?– 9:3:3:1
• Round Yellow: 9– RRYY, RrYy
• Round Green: 3– RRyy, Rryy
• Wrinkled Yellow: 3– rrYY, rrYy
• Wrinkled Green: 1– rryy
11. Independent Assortment
• The alleles for a given trait segregate independently of one another and do not influence each other’s inheritance.
12. A Summary of Mendel’s Principles
• The inheritance of biological characteristics is determined by genes that are passed down from parents to their offspring
• 13. Two or more forms of a trait may exist (ex: Dominant and Recessive)
• The copies of genes are segregated from each other when gametes are formed
• The alleles for different genes usually segregate independently from one another
Beyond Dominant and Recessive
• 14. There are some alleles that are neither dominant or recessive, and many traits:
• Genetics tends to be a bit more complicated than that:– The majority of genes have more than two alleles,
and important traits are controlled by many different genes.
15. Incomplete Dominance
• Cases in which one allele is not dominant over the other– The heterozygous phenotype is somewhere
between the two homozygous phenotypes– Ex:• Strawberry Blonde• 4 ‘o Clock Plants
15. Codominance
• Both alleles contribute to the phenotype– Both alleles will be shown in the offspring
• Ex:– Erminette Animals• Black feathers is codominant with white• Offspring show both colors
– Humans• Proteins synthesis
15. Multipe Alleles
• Genes that have more than two possible alleles
• This does not mean that an individual can have more than two alleles for a gene– It means that there could be more than two
possibilities in a population– Ex:• Rabbit fur color• Blood Types in humans
Multiple Alleles
15. Polygenic Traits
• Traits that are controlled by two or more genes– Many traits are produced by the interaction of
several genes– Ex:• Human Skin Color• 4 genes control skin color• Human Eye Color
Applying Mendel’s Principles
• Thomas Morgan- Geneticist that worked with Fruit Flies to test Mendel’s Principles of Segregation– 16. Chose Fruit Flies because:
• Small in size• Easy to take care of in a lab setting• Capable of producing large numbers of offspring very quickly
• 17. The conclusion:– Mendel’s Principles apply to not just pea plants, but
other organisms as well
Genetics and the Environment
• 18. Genes are not the only factor for determining characteristics of an organism
• The Environment plays a role as well– Ex: Sunflower Height is determined by the genes,
but this will change depending on factors such as climate, water availability, and soil composition
Exit Slip
X
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Katy Perry Wolverine
Hair Color:-B: Black-b: Blue
Claws:-C: No Claws-c: Claws
Solve the Cross:Bbcc
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