Genetics
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Genetics
description
Genetics. How are traits passed from parents to offspring?. Chapter Introduction. Gregor Mendel. Studied heredity – the passing of traits from parents to offspring. Gregor Mendel is known as the father of genetics —the study of how traits are passed from parents to offspring. Grow quickly - PowerPoint PPT Presentation
Transcript of Genetics
• Studied heredity– the passing of traits from parents to offspring.
Gregor Mendel
• Gregor Mendel is known as the father of genetics—the study of how traits are passed from parents to offspring.
Mendel studied genetics by doing controlled breeding experiments with pea plants… Why peas?
• Grow quickly
• Come in many varieties
• Mendel could control pollination
• There are two types of pollination:
Self pollination
Cross pollination
Mendel’s Experiments• Used plants that he knew were true-
breeding
• True breeding—when a plant self-pollinates it will always produce more plants with the same traits; (is homozygous)
(a.k.a. purebred)
X =
• Mendel crossed (mated) a true-breeding purple flowered pea plant with a true-breeding white flowered pea plant
• All of the offspring had purple flowers!
X =
(Parents) (Offspring)
What happened to the white flowers?
• (Transparency demo)
• Dominant—the trait that appears if two traits are mixed (capital letter)
• Recessive—trait that is hidden if 2 traits are mixed (lowercase)
• Purple flowers are dominant over white flowers
hybrid
Science Use the offspring of two animals or plants with different forms of the same trait
Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor
Mendel’s Results (cont.)
Mendel’s Experiments continued…
• Mendel also cross-pollinated hybrid plants.
X =
Parents
Offspring
75%
25%
Mendel’s Experiments continued…
• The trait for white flowers showed up again!
• He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.
75%
25%
Mendel’s Experiments continued…
Mendel concluded that two factors, one from each sperm and one from each egg, control each inherited trait.
• The factors that Mendel talked about are called genes
• A gene is a section on a chromosome that has genetic information for one trait.
Gene
Genes continued…
• One trait/gene may have a few different varieties
• Example: hair color
• The different forms of a gene are called alleles
brown
red
blonde
Genotype• The GENetic code (or combination of
alleles) of an organism is called its GENotype
• Shown as 2 letters per trait
• Example: someone with brown hair might be BB
One allele from mom
One allele from dad
• When the two alleles of a gene are the same, the genotype is true breeding, or homozygous.
• If the two alleles of a gene are different, the genotype is hybrid, or heterozygous.
What Controls Traits (cont.)
Check this out…
• B= brown hair b=blonde hair
• BB
• Bb
• bb
Brown Hair
Blonde Hair
Brown Hair
Homozygous (true-breeding)
Heterozygous (hybrid)
Homozygous (true-breeding)
Lets see how quick you are….• P = purple flowers in pea plants, p= white
flowers in pea plants
• PP
• Pp
• pp
Purple
Purple
White
What letters do you use?
• Choice of letter code is up to you…
• Usually the first letter of the trait
• Capital letter means the trait is dominant
• Lower case means it is recessive
• The PHenotype is the PHysical appearance of the organism
• Example: brown hair, purple flowers, blue eyes
Phenotype
A Punnett Square is a model used to predict possible genotypes and phenotypes of offspring.
•Bb x Bb
B
B
b
b
BB
Bb
Bb
bb
Probability- the mathematical chance an event will occur
• Bb x Bb
• Probability of Brown: 3 out of 4; 75%
• Probability of blue: 1 out of 4; 25%
B
B
b
b
BB
Bb
Bb
bbbrownbrown
brown blue
Phenotypic Ratio
•Bb x Bb
•Probability of Brown: 3 out of 4; 75%
•Probability of blue: 1 out of 4; 25%
•Phenotypic Ratio is 3:1 (Brown:blue)
B
B
b
b
BB
Bb
Bb
bb
brownbrown
brown blue
Genotypic RatioBb x Bb
•Probability of BB: 1 out of 4; 25%
•Probability of Bb: 2out of 4; 50%
•Probability of bb: 1 out of 4; 25%
•Genotypic Ratio is 1:2:1 (BB:Bb:bb)
B
Bbb bb
BB
Bb
Bb
bb
brown
brown
brown
blue
A pedigree shows phenotypes of genetically related family members.
Modeling Inheritance (cont.)
• Sometimes traits appear to be blends of alleles.
• Alleles show incomplete dominance when the offspring’s phenotype is a blend of the parents’ phenotypes.
Complex Patterns of Inheritance
• Mixing of two traits (blending)
• One dominant allele is only “half-strong”
• Red + white = pink
R=red
r=white
• Codominance occurs when both alleles can be observed in a phenotype.
Complex Patterns of Inheritance
Codominance• Both alleles are expressed at the same
time in the phenotype
• Red fur + white fur = roan fur (red and white mixed)
R=red
r=white
