genetics and mendel. gregor mendel austrian monk studied peas 1860 (darwin’s voyage ended 1836)...
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Genetics and Genetics and MendelMendel
Gregor MendelGregor Mendel
• Austrian Monk • Studied peas 1860
(Darwin’s voyage ended 1836)
• Developed laws of inheritance of traits
• Did not know about genes or DNA
Mendel’s ExperimentsMendel’s Experiments
Mendel’s PeasMendel’s PeasAfter many test crosses of plants Mendel decided some traits were dominant (expressed) and some
traits were recessive (not expressed) but still resided in the organism
Law of DominanceLaw of Dominance
• Only the dominant trait will appear in the offspring
• The other trait does not appear and is recessive
When crossing two purebred individuals:
Mendel’s Laws of Mendel’s Laws of InheritanceInheritance
• Each individual has two factors for each traitEach individual has two factors for each trait• The factors segregate (separate) during the The factors segregate (separate) during the
formation of gametesformation of gametes• Each gamete contains only one factor from each Each gamete contains only one factor from each
pair of factorspair of factors• Fertilization gives each new individual two factors Fertilization gives each new individual two factors
for each traitfor each trait• Factors sort independently of each otherFactors sort independently of each other
• All possible combinations of factors can occur in All possible combinations of factors can occur in the gametesthe gametes
Modern GeneticsModern Genetics• Each person has two alleles for each trait, one
on each homologous chromosome• Meiosis separates the alleles when gametes are
formed• Each gamete receives one of the alleles
• Fertilization gives each new individual two alleles for each gene of a trait
• During metaphase I the tetrads arrange randomly at the equatorial plane
• All possible combinations are in the gametes
AllelesAlleles• Alternate forms of the same gene• Dominant alleles –
– expressed – capital letter used
• Recessive alleles – – suppressed by the dominant allele – not expressed– Lower case letter used
• Gene locus - – specific location on homologous
chromosomes
Homozygous vs. Homozygous vs. HeterozygousHeterozygous
• Homozygous –– Two identical alleles for the trait
• Heterozygous –– Two different alleles for the trait
Homozygous dominant for shape
Heterozygous for pod color
Genotype vs. PhenotypeGenotype vs. Phenotype
• Genotype – Genotype – – Alleles received Alleles received – Genetic code of the Genetic code of the
individualindividual
• PhenotypePhenotype– Physical Physical
appearanceappearance– Gene expressionGene expression
Genotype is homozygous dominant for
shapePhenotype is
Round
Genotype is heterozygous
for color Phenotype is Green pod
color
Genotype vs. PhenotypeGenotype vs. Phenotype
Genotypes? Phenotypes?
Homozygous
recessive
Heterozygous
Wrinkled
Green pod
color
• Humans Humans Alleles for finger length:Alleles for finger length:– Short is dominantShort is dominant– Long is recessiveLong is recessive
• What letter will indicate the dominant allele?What letter will indicate the dominant allele?
S (capital)S (capital)
• What letter will indicate the recessive allele?What letter will indicate the recessive allele?
s (lower case)s (lower case)
Genotype vs. PhenotypeGenotype vs. Phenotype
What are the possible genotypes and phenotypes?What are the possible genotypes and phenotypes?
GenotypesGenotypes Phenotypes Phenotypes
Genotype vs. PhenotypeGenotype vs. Phenotype
SS
Ss
ss
Short Fingers
Short Fingers
Long Fingers
• Mendel discovered that tall pea plants Mendel discovered that tall pea plants (T) were dominant over short pea (T) were dominant over short pea
plants (t). plants (t).
• If the phenotype of a pea plant is short, If the phenotype of a pea plant is short, what is its genotype?what is its genotype?
• Explain:Explain:The short gene is recessive. To be The short gene is recessive. To be
expressed, both recessive genes must be in expressed, both recessive genes must be in the genotypethe genotype
Genotype vs. PhenotypeGenotype vs. Phenotype
tt
Predicting ResultsPredicting ResultsPunnett Square: predicts the probability of the
offspring having a specific genotype and phenotype
STEPS:
1) Assign a symbol for each allele
2) Determine genotype of each parent
3) Determine all possible gametes each parent can produce (set up Punnett square)
4) Determine all allele combinations of offspring
5) Determine phenotype of each offspring from genotype
Given:
Purple flowers are dominant over white flowers Two heterozygous purple flowers are crossed
Predicting ResultsPredicting Results
1)Assign a symbol for each allelePurple: PWhite: p
2)Determine genotype of each parentHeterozygous: Pp
Given: Purple flowers are dominant over white flowers Two heterozygous purple flowers are crossed
Predicting ResultsPredicting Results
3) Determine all possible gametes each parent can produce 4) Determine all allele combinations of offspring
Father’s gametes
Mother’s gametes
P
P
p
p p
p
ppP
PP PFirst write the letters at the top of each column in each square below
Then write the letters at the beginning of each row in each square across
Separate and write one parent’s alleles across the top of each columnPlace the other parent’s alleles down the side in front of each row
Predicting ResultsPredicting ResultsGiven: Purple flowers (P) are
dominant over white flowers (p) Two heterozygous purple flowers are crossed P
P
p
p p
p
ppP
PP P5) Determine phenotype of
each offspring from genotype
PP = 1 Purple
Pp = 2 Purple
pp = 1 WhiteWhat percentage of offspring are purple? What percentage of offspring are white?
¾ = 75%¼ = 25%
Genotypes vs. Genotypes vs. PhenotypesPhenotypes
Which color is dominant?
Which color is recessive?
Which plants are homozygous?
Which plants are heterozygous?
GenerationsGenerations
• The original parents: – Called the P generation
– Produce P gametes
• Offspring of P generation: – Called the F1 generation
– Produce F1 gametes
Two Trait InheritanceTwo Trait Inheritance
Yellow (YY)
Round (RR)
(YYRR)
Green (yy)
Wrinkled (rr)
(yyrr)
P gametes YR yr
YyRrF1 Generation
Only combinations possible since they are homozygous for both traits
Two Trait InheritanceTwo Trait InheritanceYellow, Round (YyRr)
F1 gametes: YR Yr yR yr
YR
YR
Yr
Yr
yR
yR
yr
yr
Y
Y
Y
Y
Y
Y
Y
Y
RR
RR
RR
RR
r
r
r
r
r
r
r
r
y
y
y
y
y
y
y
yY R Y R Y R Y R
Y r Y r Y r Y r
y R y R y R y R
y r y r y r y r
FF22 Generation Generation
YR
YR
Yr
Yr
yR
yR
yr
yr
YYRR
YYRr
YyRR
YYrr YyRr Yyrr
YyRrYyRRYYRr
YyRr
yyRR
Yyrr
YyRr
yyrryyRr
yyRr
How many: Yellow Smooth? Yellow wrinkled? Green Smooth? Green wrinkled?
9 33 1
What to Know:What to Know:
• Know and apply terminology for geneticsKnow and apply terminology for genetics
• Describe genotypes and phenotypesDescribe genotypes and phenotypes
• Identify and explain dominant and Identify and explain dominant and recessive traits recessive traits
• Identify gametes of parents for one and Identify gametes of parents for one and two traitstwo traits
• Set up and complete Punnett squares for Set up and complete Punnett squares for both one and two traitsboth one and two traits