Bell Ringer Look at your classmates. Note how they vary in the shape of the front hairline, the space between the two upper front teeth, and the way.
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Bell Ringer
Look at your classmates. Note how they vary in the shape of the front hairline, the space between the two upper front teeth, and the way in which the earlobes are attached.
Make a list of the different forms of these traits that you have observed in the class or among other people you know.
1. Could these traits be inherited? From whom could they be inherited?
2. How is it possible that these traits could be found in a person and his or her biological grandparents but not in the biological parents?
Bell Ringer
1. Could these traits be inherited? From whom could they be inherited?
2. How is it possible that these traits could be found in a person and his or her biological grandparents but not in the biological parents?
Bell Ringer
1. Could these traits be inherited? From whom could they be inherited?
Yes; from parents.
2. How is it possible that these traits could be found in a person and his or her biological grandparents but not in the biological parents?
Bell Ringer
1. Could these traits be inherited? From whom could they be inherited?
Yes; from parents.
2. How is it possible that these traits could be found in a person and his or her biological grandparents but not in the biological parents?
Genes are passed from generation to generation, but are not necessarily expressed in every generation.
3. Every living thing – plant or animal, microbe or human being – has a set of characteristics inherited from its parents.
Gregor Mendel
In 1865, Gregor Mendel published studies of inheritance in pea plants.
During sexual reproduction, male and female gametes join to form a zygote in the process known as fertilization.
Genetics= the scientific study of heredity.
Heredity is… the passing
on of traits from parents to offspring.
1. Controlled by “factors.”
2. Passed from generation to generation.
3.Probability (pg. 267)
4. Traits – characteristics that are inherited.
1902 – Chromosome Theory of Heredity
Genes (Mendels “factors”) are located on chromosomes. Genes are segments of DNA. Genes are traits
The different forms (variations) of a gene are called Alleles.
This is the basis for the modern science of Genetics.
Genetic Principles
1. Alleles – gene form, Y or y, for each variation of a trait of an organism.
2. Dominant or Recessive
D= visible, observable trait of an organism that masks a recessive form of a trait.
R = a hidden trait of an organism that is masked by a dominant gene.
3. Separation, or Segregation; each allele will segregate or separate from each other and it will ½ chance that you receive either allele. Ex. Y or y
4. Independent Assortment
Other Terms
Phenotype – the way an organism looks and behaves. Physical characteristics of an organism.
Genotype – the gene combination of an organism; the genetic make-up of a trait or gene.
Homozygous – when an organisms two alleles for a trait are the same. Homozygous recessive ex. rr; homozygous dominant ex. RR
Heterozygous – when an organisms two alleles for a trait are not the same.
Genes VS Alleles
Gene Plant Height Flower Color
AlleleTall Plant Purple Flowers
Short Plant White Flowers
R.C. Punnett
In 1905, R.C. Punnett introduced the Punnett square.
Punnett squares can be used to predict and compare the genetic variations that will result from a cross (pg. 268).
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y
y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y
y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy
y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy
y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy
y Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy
y Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy Yy
y Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy Yy
y Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
Parents (P)
Y Y
y Yy Yy
y Yy Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype: YY x yy
Phenotype: Yellowx green
All (100%) offspring in F1 Generation are Yellow hybrids.
Parents (P)
Y Y
y Yy Yy
y Yy Yy
Monohybrid CrossGenotype: Yy x Yy
Phenotype: Yellow x Yellow
Phenotypic Ratio:
75% (3/4) offspring are Yellow; Ratio is 3:4 (Yellow : total)
25% (1/4) offspring are green; Ratio is 1:4 (green : total)
F1 Generatio
nY y
Y YY Yy
y Yy yy
Dihybrid Cross
Round pea seed (R) is dominant to wrinkled pea seed (r).
FOIL: YyRr YR, Yr, yR, yr
(These are the possible genotypic combinations)
Dihybrid CrossRound pea seed (R) is dominant to
wrinkled pea seed (r). Possible
Combinations
YR Yr yR yr
YR
Yr
yR
yr
Dihybrid CrossRound pea seed (R) is dominant to
wrinkled pea seed (r). Possible
Combinations
YR Yr yR yr
YR YYRR YYRr YyRR YyRr
Yr YYRr YYrr YyRr Yyrr
yR YyRR YyRr yyRR yyRr
yr YyRr Yyrr yyRr yyrr
What is the probability that the plant will produce:
Yellow, Round Peas:
Yellow, Wrinkled Peas:
Green, Round Peas:
Green, Wrinkled Peas:
Possible
CombosYR Yr yR yr
YRYYRR
Yellow, Round
YYRrYellow, Round
YyRRYellow, Round
YyRrYellow, Round
YrYYRr
Yellow, Round
YyrrYellow,
wrinkled
YyRrYellow, Round
YyrrYellow,
wrinkled
yRYyRR
Yellow, Round
YyRrYellow, Round
yyRRgreen, Round
yyRrgreen, Round
yrYyRr
Yellow, Round
YyrrYellow,
wrinkled
yyRrgreen, Round
Yyrrgreen,
wrinkled
What is the probability that the plant will produce:
Yellow, Round Peas: 9/16
Yellow, Wrinkled Peas: 3/16
Green, Round Peas: 3/16
Green, Wrinkled Peas: 1/16
Possible
CombosYR Yr yR yr
YRYYRR
Yellow, Round
YYRrYellow, Round
YyRRYellow, Round
YyRrYellow, Round
YrYYRr
Yellow, Round
YyrrYellow,
wrinkled
YyRrYellow, Round
YyrrYellow,
wrinkled
yRYyRR
Yellow, Round
YyRrYellow, Round
yyRRgreen, Round
yyRrgreen, Round
yrYyRr
Yellow, Round
YyrrYellow,
wrinkled
yyRrgreen, Round
Yyrrgreen,
wrinkled
To find the probability that two different events will happen at the same time, multiply the
probabilities of each event happening
separately.
To find the probability that two different events will happen at the same time, multiply the
probabilities of each event happening separately.
Probability of offspring having YELLOW pea seeds:
¾
Probability of offspring having ROUND pea seeds:
¾
Probability of offspring having BOTH YELLOW AND ROUND PEAS:
¾ X ¾ = 9/16
Trihybrid Cross
Tall Stem (T) is dominant to short stem (t).
The probability of producing tall stems in a monohybrid cross is:
What is the probability that the offspring in a trihybrid cross will be Yellow, Round, and Tall?
Trihybrid Cross
Tall Stem (T) is dominant to short stem (t).
The probability of producing tall stems in a monohybrid cross is:
¾ What is the probability that the offspring in
a trihybrid cross will be Yellow, Round, and Tall?
¾ X ¾ X ¾ = 27/64
Incomplete dominance (also called partial dominance) occurs when the phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. For example, the snapdragon flower color is either homozygous for red or white. Example: Red flowers
(RR) crosses with white flowers (WW) shows incomplete dominance for pink flowers (RW)
Codominance – when both alleles contribute to the phenotype.
Example – black feathers codominant with white feathers in chickens, both white and black feathers are present separately. Also blood types and a cholesterol enzyme in humans.
Other Terms
Multiple alleles-genes that have more than 2 allelesThis means that there are more than 2
possible alleles in a population Example: rabbit fur colors
Polygenic traits – traits controlled by more than 2 genes Example: human skin color is controlled by
more than 4 different genes
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