Ch14 Mendel
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Mendel
P generation – true-breeding
• Why pea plants?• distinct heritable
features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits
• He could control mating between plants
• Small• Matures quickly
Results:• 1. Mendel produced 14
pure strains by self-pollination
• ------> P generation
• 2. cross-pollinated plants w/contrasting traits
• -----> F1 generation
• 3. self-pollinated F1 generation
• -----> F2 generation
• 4. counted and found ratios of traits
Figure 11.3-3
P Generation
Experiment
(true-breedingparents)
F1 Generation
F2 Generation
(hybrids)
Purple flowers White flowers
All plants had purple flowers
Self- or cross-pollination
705 purple-floweredplants
224 white-floweredplants
Would these results seem strange to you if you were Mendel?
Table 11.1
Good experiments have large sample sizes
What we now know
Figure 11.4
Allele for purple flowers
Pair of homologouschromosomes
Allele for white flowers
Locus for flower-color gene
Law of segregation• Each gamete only gets one allele for a gene
law of independent assortment• - alleles for different genes distribute to gametes
independently• i.e. dominant traits don't always get passed on with other
dominant traits
Are the alleles on the same chromosome or different chromosomes?
Punnett Square
Copy this down!For every problem, you must:
1. Define alleles
2. Define cross
3. Show work: Punnett Square
4. Box final answer
monohybrid cross• A cross between individuals that are heterozygous for one
character
Use your white board to solve• A brown eyed man whose mother was blue-eyed marries a
blue-eyed woman. • What is genotypic ratio of their potential offspring?• What are their phenotypes? • What is the probability that they will have two blue-eyed
children?
• Define alleles.• Define cross.• Show work/punnett square.• Box final answer.
Answer:• A brown eyed man whose mother was blue-eyed marries a blue-eyed
woman. • What is genotypic ratio of their potential offspring?• What are their phenotypes? • What is the probability that they will have two blue-eyed children?
• Define alleles.• Define cross.• Show work/punnett square.• Box final answer.
How can we tell the genotype of an individual with the dominant phenotype?
Figure 11.7 Technique
Predictions
Dominant phenotype,unknown genotype:
PP or Pp?
Eggs
Sperm
½ offspring purple and
½ offspring white
Recessive phenotype,known genotype:
pp
If purple-floweredparent is PP
If purple-floweredparent is Pp
Eggs
Sperm
All offspring purple
Results
or
or
p p
P
p
Pp
pp
Pp
pp
p p
P
PPp
Pp
Pp
Pp
• Possible genotypes?
• testcross: breeding the mystery individual with a homozygous recessive individual
• If any offspring display the recessive phenotype, the mystery parent must be heterozygous
Let’s try…• Imagine your candy preference is genetic.
• S = Snicker’s allele• s = Twix allele
• 7 kids like Snicker’s; 1 kid likes Twix
Answer:• Imagine your candy
preference is genetic.• S = Snicker’s allele• s = Twix allele
• 7 kids like Snicker’s; 1 kid likes Twix
dihybrid cross• A cross
between individuals that are heterozygous for two characters
Independent Assortment• Assume characters on different chromosomes
Memorize this pattern:
Memorize this pattern:
Answer:
You try:
• In humans, curly hair and freckles are dominant. A man with curly hair whose mom had straight hair mates with a woman who has straight hair. Both parents are heterozygous for freckles.
• What are the chances of having a child with straight hair and freckles?
• What would be the chance of a child having curly hair and no freckles?
• What about having two children with this phenotype?
Answer:• In humans, curly hair and freckles are dominant. A man with curly hair whose mom
had straight hair mates with a woman who has straight hair. Both parents are heterozygous for freckles.
• What are the chances of having a child with straight hair and freckles?
• What would be the chance of a child having curly hair and no freckles?
• What about having two children with this phenotype?
Probability:Figure 11.9
R r
R
r
Rr
Segregation ofalleles into eggs
Eggs
Sperm
¼
½ ½
½
½
Segregation ofalleles into sperm
Rr Rr
RR
¼
rr
¼
Rr
¼
Rule of Multiplication: “and”
• What is probability of getting:
• Heads and then a Tails
• Heads three times in a row
• A of hearts and then a Black Jack (w/replacement)
Rule of Addition: “or”• What is probability of getting:
• Heads or a Tails
• A of hearts or a Black Jack (w/replacement)
Let’s try a 2nd method for solving dihybrids:•CcFf x ccFf• What are the chances of
having a child with straight hair and freckles?
• What would be the chance of a child having curly hair and no freckles?
Trihybrids and beyond…
•AaBbCc x AABbCC• What is the probability of getting AaBbCc or AABBCC?