genetics chapter 12. 12-1: origins of hereditary science
TRANSCRIPT
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Genetics
Chapter 12
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12-1: Origins of Hereditary Science
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Mendel’s Experiments
Genetics – The study of how characteristics are transmitted from parents to offspring
Heredity – The passing on of genetic characteristics from one generation to another
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Mendel’s Experiments
Gregor Mendel (an Austrian monk) used cross-pollination techniques in which pollen is transferred between flowers of two different plants.
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Mendel’s Experiments
Reasons Mendel used pea plants Require little care Produce many offspring Mature quickly (8-10 weeks)
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Mendel’s Experiments
P (parental) generation – Organisms that are true-bred for specific traits
F1 generation – Offspring of the P generation
F2 generation – Offspring of the F1 generation F = Filial (pertainting to a son or daughter)
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Mendel’s Experiments
Self-pollination – A plant with both male and female reproductive organs that fertilizes itself
Cross-pollination – Pollen from one plant is carried to the flower of another plant
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Mendel’s Experiments
Three Steps of Mendel’s Experiments
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Mendel’s Experiments
Gene – A section of DNA that carries the information on how to make one protein
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Mendel’s Experiments
Allele – An alternative form of a gene
One allele for each trait is passed from each parent to the offspring.
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Mendel’s Experiments
Dominant trait – An allele that is fully expressed whenever the allele is present in an individual The trait that masks the
other Recessive trait – An allele
that is expressed only when there is no dominant allele present in an individual The trait that is masked
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12-2: Genetic Crosses
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Monohybrid Cross
Monohybrid cross – A cross in which one characteristic is tracked
Punnett square – used to predict the outcome of genetic crosses
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Monohybrid Cross
Genotype – the genetic makeup of an organism (use letters)
Phenotype – the appearance of an organism (physical appearance)
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Monohybrid Cross
Homozygous – having identical alleles Heterozygous – having different alleles
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Monohybrid Cross
Trait – Plant height Phenotype
T – tall t – short
Genotype TT – homozygous
dominant (pure bred) Tt – heterozygous
(hybrid) tt – homozygous
recessive (pure bred)
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Monohybrid Cross
Probability – the likelihood that a specific event will occur
Probability = number of one kind of possible outcome
total number of all possible outcomes
A probability may be expressed as a decimal, a percentage, or a fraction
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Mendel’s Characteristics
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Monohybrid Cross
Ratios and percentages TT x tt = 100% heterozygous TT x TT = 100% homozygous dominant tt x tt = 100% homozygous recessive Tt x tt
50% heterozygous 50% homozygous recessive
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Monohybrid Cross
Ratios and percentages Tt x Tt = Genotypic ratio – 1:2:1 ratio
25% homozygous dominant 50% heterozygous 25% homozygous recessive
Tt x Tt = Phenotypic ratio – 3:1 75% tall 25% short
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Dihybrid Cross
Dihybrid cross – A breeding experiment that tracks the inheritance of two traits
Example Traits: Seed shape & Seed color Alleles: R – round
r – wrinkled Y – yellow y – green
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Dihybrid Cross
Use the FOIL method for each parent to set-up the Punnett square
RrYy x RrYy
RY Ry rY ry RY Ry rY ry
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Dihybrid Cross
RY
Ry
rY
ry
RY Ry rY ry
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24
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RY Ry rY ry
RY
Ry
rY
ry
Dihybrid Cross
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This chart is used to illustrate the variety of eye colors
The trait for eye color actually has three alleles:
AaBbCc
Why eye color changes in people is unknown
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Other Monohybrid Crosses
Incomplete dominance – a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele This results in a
combined phenotype.
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Other Monohybrid Crosses
Codominance – Two alleles are expressed (multiple alleles) in heterozygous individuals Two alleles that are both dominant
Example: blood typesKey
A = IA
B = IB
O = I
A and B are dominant over O
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Other Monohybrid Crosses
Genotypes Phenotypes Type A = IAIA or IAi AA or AO Type B = IBIB or IBi BB or BO Type AB = IAIB AB Type O = ii OO
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Other Monohybrid Crosses
Sex-Linked traits – Traits (genes) located on sex chromosomes X – Female sex chromosome Y – Male sex chromosome
Many sex-linked traits carried on X chromosome
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Pedigree
Pedigree – A diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships