dna – double helix dna coils to form a chromosome you receive 1 set of chromosome from mom &...
TRANSCRIPT
DNA – double helix
• DNA coils to form a chromosome
• You receive 1 set of chromosome from mom & one from dad
• Chromosomes have areas that code for a gene
• 1 gene = 1 protein
The Central Dogma!
Number of Genes on Chromosomes
Introduction to GeneticsChapter 9
Section 1 – Mendel’s LegacySection 2 – Genetic Crosses
Mendel’s Legacy
Gregor Mendel was a priest in the mid 19th Century. Studied different pea plants Father of GENETICS – the scientific
study of heredityWhat is heredity?-passing down of
physical characteristics from parent to offspring
Mendel’s ExperimentsSelf pollinated
Developed a method of cross pollination
P generation, F1 generation, F2 generation
TRAITS: plant height, flower position, pod color, pod appearance, seed texture, seed color, flower color
The Outcome of Mendel’s WorkIn all of Mendel’s experiments
First generation ONLY produced one form of the trait (i.e. tall)
Second generation the “lost” form the trait reappeared in about ¼ of the plants
Mendel’s Findings TODAYFactors that control the traits are called
GENES.Alleles – contrasting forms of a gene
i.e. Tall vs. Short; round vs. wrinkled Inherited from parents Dominant Allele – trait always shows up
when the allele is present Recessive Allele – “masked” or hidden by
the dominant trait
TERMS TO KNOW Phenotype – the physical characteristic
displayed by the organism (PHYSICAL = PHENOTYPE)
Genotype – the actual combination of alleles held by the organism (GENOTYPE = GENES)
Genotype = Rr
Phenotype = Red
Mendel concluded that the paired “factors” or alleles separate when making reproductive cells This means that each gamete only gets one
copy of each allele When fertilized, the offspring would have 2
copies
Law of Segregation Alleles are segregated or separated during
the formation of gametes.
Mendel also observed that dominant traits do not always appear together.
Mendel concluded that these factors are not connected
Law of Independent Assortment“Factors” or alleles for different
characteristics are distributed to gametes independently
Explain this in YOUR words
Representing AllelesUse letters to represent alleles
Use the same letter for one trait (T for height)
Capital letter for dominant (T = Tall) Lowercase letter for recessive letter (t =
short)T T
t Tt Tt
t Tt Tt
Purebred Tall Parent
Purebred Short Parent
Hybrid Offspring
Genetic Crosses
What is the chance that a coin will land on heads?
Probability – a number that describes how likely it is that an event will occur.
Interdependence of Events
If you toss a coin once and then toss again, the first toss does not affect the second
Each TIME you toss the coin, you have a 1 in 2 chance of getting heads.
Probability & GeneticsHow is probability related to
Genetics? (Think about Mendel’s results)
Each time Mendel repeated his experiment, he got similar results. WHY?
Mendel was the first to discover that you could PREDICT the outcome of a cross.
Purebred Tall Plant X Purebred Short Plant
ALL TALL PLANTS
Punnett SquaresTool used by scientists to determine
the outcome of a genetic crossShows all the possible combinations
of offspring
T T
t Tt Tt
t Tt Tt
Purebred Tall Parent
Purebred Short Parent
Hybrid OffspringOUTCOME: TALL OFFSPRING
Monohybrid Crosses Involves ONE PAIR of contrasting traits Homozygous – purebred (has the same
type of alleles) Heterozygous – hybrid (has two types of
alleles)
T T
t
t
Genetic cross between a tall plant and a short plant
Genetic cross between 2 heterozygous tall plants
T t
T
t
TERMS TO KNOW Phenotype – the physical characteristic
displayed by the organism (PHYSICAL = PHENOTYPE)
Genotype – the actual combination of alleles held by the organism (GENOTYPE = GENES)
Genotype = Rr
Phenotype = Red
Ratio’s Phenotypic Ratio – the ratio of
phenotypes that appear in the offspring Genotypic Ratio – the ratio of genotypes
that appear in the offspring
Genotypic Ratio = 4:0
Phenotypic Ratio = 4:0
Monohybrid Punnett Square Review
Heterozygous Tall x Heterozygous TallGive phenotypic and genotypic ratios
TT x TtGive phenotypic and genotypic ratios
Dihybrid Crosses Involves TWO PAIRS of contrasting traits Homozygous – purebred (has the same
type of alleles) Heterozygous – hybrid (has two types of
alleles)Genetic cross between a Purebred tall
plant, purple flower and a Purebred short plant, white flower
TTPP x ttpp
What are the possible gametes?
(ALL THE POSSIBLE COMBINATION OF GAMETES)
Determining Gametes – all possible combinations
PARENT 1 TtPp
TP Tp tP tp
PARENT 2 TtPp
TP Tp tP tp
What are the possible gametes for these parents?
Heterozygous Tall plant w/ purple flower (TtPp) x Heterozygous Tall plant w/ purple flower
(TtPp)TP Tp tP tp
TP
Tp
tP
tp
Other Types of DominanceIncomplete Dominance
Two or more alleles influence the phenotype
An intermediate phenotype results; a blending of traits Red Flower x White Flower
(RR) (rr)
Pink Flower
(Rr)
Red Flower x White Flower
Outcome =ALL PINK FLOWERS
R R
r Rr Rr
r Rr Rr
Incomplete dominance Punnett Squares
Pink Flower x Pink Flower
Outcome =Red, White & Pink
Flowers
R r
R RR Rr
r Rr rr
Other Types of DominanceCodominance
Two or more alleles are expressed in the phenotype
A combination phenotype results
Red Cow x White Cow
(RR) (WW)
Roan Cow
(RW)
Red Cow x White Cow
Outcome =ALL ROAN COWS
R R
W RW RW
W RW RW
Codominance Punnett Squares
Roan Cow x Roan Cow
Outcome =Red, White & Roan Cows
R W
R RR RW
W RW WW