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History: Gregor Mendel Austrian monk that studied pea plants Papers were rediscovered in 1900 Called Father of Genetics
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7.1MENDEL & ONE TRAIT CROSSES
Lesson Objectives Students will be able to:
Explain the major experiments conducted by Gregor Mendel
Define genes, alleles, genotype, phenotype
Demonstrate mastery of one-trait crosses by using punnett squares to complete genetics problems
History: Gregor Mendel 1822-1884 Austrian monk that studied pea
plants Papers were rediscovered in 1900 Called Father of Genetics
Genes & Alleles Genes:
Sequence of nucleotides on chromosome Codes for a protein
Alleles: Variations of a gene (create versions of the
same protein) Example: tall & short Each individual has two alleles for each
gene - diploid One allele from each parent (gametes fused) Homologous chromosomes
Genes & Alleles Alleles can be:
Dominant: always shown Tall: “T”
Recessive: Masked or covered up by dominant allele Short: “t”
Genotype Total of all alleles; genetic make-up
Two alleles Ex: TT, Tt, tt
Genotype types: Homozygous (same two alleles)
Homozygous dominant = TT Homozygous recessive = tt
Heterozygous (different alleles) One of each allele (Tt)
Phenotype Physical appearance of trait Examples:
Tall, short, straight, curly, etc.
Mini-quiz; T = tall; t = short Tall plant
Possible genotypes?
Phenotype?
Short plant Possible genotypes?
Phenotype?
Sexual Reproduction: Individuals are diploid – have two
alleles for each gene Human gametes: egg & sperm Gametes are haploid
Only contain one of each chromosome Have one allele for each gene
In sexual reproduction, it is totally random which allele for each gene is passed onto offspring
One-trait crosses
Single Factor Crosses
Let’s practice! Gametes can only have one allele for
each gene Homozygous dominant parent: TT
Gametes: T or T Homozygous recessive parent: tt
Gametes: t or t Heterozygote parent: Tt
Gametes: T or t
Let’s Practice! Cross: TT x tt
Determine all possible combinations of gametes One from each parent
How? Using Punnett square
Punnett Squares Cross: TT x tt
TT gametes: T or T tt gametes: t or t
F1 Genotype:
F1 Phenotype:
T T
t
t
Tt Tt
Tt Tt
Punnet Squares Cross: Tt x Tt
T = tall; t = short Tt x Tt
Gametes from parent #1: T or t Gametes from parent #2: T or t
Make a punnett square representing this cross and its results
Tt x Tt
TT TtTt tt
T t
T
t
TT
Tt
Tt tt
F1 cross results T = tall; t = short Genotypes: TT, Tt, tt
Genotypic ratio: 1:2:1 Phenotypes: tall, short
Phenotypic ratio: 3: 1
Practice Problem T = tall; t = short Cross a heterozygous tall plant with a
homozygous recessive plant What are the expected genotypes and
phenotypes of the offspring?
7.1 Practice Problems