Genetics Objectives Learn basic terms Genetics gene allele locus recessive dominant codominance homozygote heterozygote phenotype genotype Mendels experiments on pea plants Punnett ID: 299277
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Slide1
Lecturer: David
GeneticsSlide2
Objectives
Learn basic terms
Genetics, gene, allele, locus, recessive, dominant,
codominance
, homozygote, heterozygote, phenotype, genotype
Mendel’s experiments on pea plants
Punnett
squares
Be
able to identify the
phenotype and genotype ratiosSlide3
What is genetics?
Genetics is the science that studies heredity, the inheritance of traits from one generation to the next
Gene – DNA that codes for a particular
productSlide4
Chromosomes
46 Chromosomes
1 from each parent
XX versus XYSlide5
Definitions
Homologous chromosomes – Chromosomes with similar genes at the same loci
Locus – a particular position in a chromosome; a specific location on the chromosome
Allele – alternate forms of a gene found on a locusSlide6
Mendel and his pea plants
Mendel conducted an experiment by crossing pea plants with green and yellow peas.
Dominant allele
Y
Recessive allele
y Slide7
Heterozygote
&
Homozygote
Heterozygote – a person with 2 different alleles
For the peas:
Yy = Yellow peasHomozygote – a person with 2 identical allelesFor the peas:YY = Yellow peasyy = Green peasSlide8
Questions
Why were peas who were
Yy
,
yellow?
Why were peas who were
yy
,
green?
Why were peas who were
YY,
yellow?Slide9
Genotype
The genetic makeup of a person; whether they are homozygote or heterozygote
Phenotype
Physical characteristics of an individual’s genotype
Genotype versus phenotypeSlide10
Punnett
Squares!
Which is the recessive allele?
Which is the dominant allele?
Which ones are homozygous?
Which ones are heterozygous?Slide11
Co-dominance
Co-dominance occurs when BOTH alleles are expressed. There is a mixture of phenotypes or both phenotypes are expressed. Slide12
Example
What is this an example of?
Why?Slide13
What is this an example of?Slide14
Parental and filial generations
The generation you begin with to determine the genotype of subsequent generations is the parental generation
P
Any following generations are called filial
F1, F2, F3Slide15
Question
You decide to cross a purple flower (
Pp
) and and a yellow flower (
pp
). What are the genotypic ratios for the F1 generation? What about the phenotypic ratios? (P is dominant allele, p is recessive allele)Slide16
Answer
Genotype: 1Pp:1pp
Phenotype: 1:1 (
purple:yellow
)Slide17
Question
You decide to cross a heterozygote green pea (
Gg
) and a heterozygote green pea (
Gg
). What are the genotypic and phenotypic ratios of the F1 generation? (G – allele for green, g – allele for brown)Slide18
Answer
Genotype: 1GG:2Gg:1gg
Phenotype 3:1 (
green:brown
)Slide19
Question
You decide to cross a green eyed frog (GG) with a blue eyed frog (
gg
). What would the phenotypic and genotypic ratios be for the F1 generation? (G – dominant allele, g – recessive allele)Slide20
Answer
Genotype: 100%
Gg
Phenotype: 100% green eyed frogsSlide21
Question
You decide to cross a frog from the F1 generation of the previous question with a green eyed frog from the P generation. What do you expect your genotypic and phenotypic ratios to be? Slide22
Answer
Genotype: 1GG:1Gg
Phenotype: 100% green eyed frogsSlide23
Question
You now decide to cross two F1 generations. What phenotypic and genotypic ratios do you expect for the F2 generation? Slide24
Answer
Genotype: 1GG:2Gg:1gg
Phenotype: 3:1 (green
eyed:blue
eyed)Slide25
Question
You performed a cross between 2 flower plants. 100% of your flowers are red. What are the possible genotypes for the parental generation? (R – dominant allele, r – recessive allele)Slide26
Answer
The parental cross was either:
RR x
rr
Rr
x RR Slide27
Question
What percentage of heterozygotes would you expect from a cross between 2 blue birds? (The allele for blue is recessive)Slide28
Answer
No heterozygotes expectedSlide29
Question
What percentage of heterozygotes and homozygotes would you expect from a cross between 2 red birds (
Rr
)? Slide30
Answer
50% homozygotes
50% heterozygotesSlide31
Question
A heterozygous bean plant was crossed with a homozygous bean plant. What percentage of homozygotes and heterozygotes would you expect? (R – dominant allele, r – recessive allele)Slide32
Answer
50% heterozygotes
50% homozygotes Slide33
FYI
Monohybrid vs.
dihybrid
crosses
Monohybrid cross – cross of individuals
that contrast by 1 traitDihybrid cross – cross of individuals with 2 different traitsSlide34
Dihybrid
crossSlide35
Objectives
Learn basic terms
Genetics, gene, allele, locus, recessive, dominant,
codominance
, homozygote, heterozygote, phenotype, genotype
Mendel’s experiments on pea plants
Punnett
squares
Identify phenotype and genotype
ratiosSlide36
Lab today
Today you will be conducting a genetics lab with corn
For the first exercise you will be studying the cross between parental and F1 corn.
For the second exercise you will be studying the the F2 generation