genetics & heredity mendel and his peas. heredity – the passing of traits from parents to...
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GENETICS & HEREDITY
Mendel and His Peas
Heredity – the passing of traits from parents to offspring
Gregor Mendel – “father of genetics” Austrian monk performed experiments on peas
to help answer questions about genetics
Genetics – the study of how traits are passed from parents to offspring
Gregor Mendel
Mendel’s First Pea Experiment Cross-pollinated
Purple flowers x purple flowers = all purple flowers
White flowers x white flowers = all white flowers
Purple flowers x white flowers = all purple flowers
Mendel’s Second Pea Experiment Self-pollinated the hybrid flowers from
the first generation (the offspring that were a result of the purple flowers x white flowers)
Results: some offspring were purple
and some were white
Mendel’s Conclusions
Dominant and Recessive Dominant Trait
a genetic factor that blocks another genetic factor (ex. purple color (P))
Recessive Trait a genetic factor that is blocked by the presence
of a dominant factor (ex. white color (p)) recessive trait is observed only when two
recessive genetic factors are present in offspring (pp)
A comparison of two numbers or quantities by division The ratio of purple to white flowers in
Mendel’s second experiment is 3 to 1 or 3:1 or 3/1
Try it: There are 14 girls and 7 boys in a
classroom. What is the ratio of girls to boys? Boys to girls?
Ratios
INHERITANCE
Genes & Alleles
Gene – a section on a chromosome that has genetic information for one trait ex. flower color
Allele – the different forms of a gene ex. purple, white
Genotype & Phenotype
Phenotype – how a trait appears, or is expressed ex. purple flowers,
blue eyes, red hair
Genotype – the two alleles that control the phenotype of a trait expressed as letters
uppercase for dominant lowercase for recessive
Homozygous and Heterozygous Homozygous – when the two alleles of a
gene are the same homozygous dominant - purple flowers (PP) homozygous recessive - white flowers (pp)
Heterozygous – when the two alleles of a gene are different ex. purple flowers (Pp)
Punnett Squares
Punnett square – a model used to predict possible genotypes and phenotypes of offspring expressed as a probability (percent chance)
• Phenotype:• Green = 75% • Yellow= 25%
• Genotype:• GG = 25%• Gg = 50%• Gg = 25%
Punnett Square Examples
Draw a Punnett square for the following breeding pair of frogs: Gg x Gg
If green skin (G) is dominant to yellow skin (g), what is the probability of the offspring being green?
Try Some Punnett Squares:
Brown eyes (BB) x Blue eyes (bb)
Freckles (Ff) x no freckles (ff)
Pedigree
Pedigree – a chart that shows phenotypes of genetically related family members Symbols: MALE FEMALE
Homozygous Dominant
Heterozygous
Homozygous recessive
Pedigree Example
PATTERNS OF INHERITANCE
Types of Dominance
Incomplete Dominance – when the phenotype of an offspring is a combination of the parents’ phenotype ex. white flower x red flower = pink flower
Codominance – when two alleles can be observed in a phenotype ex. white cow x black cow = spotted cow
Other Patterns of Inheritance Multiple Alleles
genes with more than two alleles ex. blood type (A, B, AB, O)
Sex-linked Traits alleles found on the sex chromosomes (X, Y)
Polygenic Inheritance when multiple genes determine the phenotype of
a trait ex. height