Post on 17-Dec-2015
Ideas on Inheritance Before MendelIdeas on Inheritance Before Mendel
PangenesisPangenesis Particles in the body are transmitted to the Particles in the body are transmitted to the
reproductive cellsreproductive cells
BlendingBlending Black horse X White horse =Gray horseBlack horse X White horse =Gray horse
Homunculus (small human)Homunculus (small human) Spermists believed a small fully formed Spermists believed a small fully formed
human was inside the sperm and the human was inside the sperm and the female contributed nothing but her womb!female contributed nothing but her womb!
Gregor MendelGregor Mendel(1822-1884)(1822-1884)
Augustinian monkAugustinian monk Studied the inheritance of traits in over 20,000 Studied the inheritance of traits in over 20,000
pea plantspea plants Kept meticulous notes on his dataKept meticulous notes on his data No knowledge of DNA or chromosomes No knowledge of DNA or chromosomes Father of geneticsFather of genetics
His genius was not recognized until after his deathHis genius was not recognized until after his death
The Lingo of a GeneticistThe Lingo of a Geneticist GeneGene
The unit of heredity (ex. Gene for flower color)The unit of heredity (ex. Gene for flower color) AllelesAlleles
Alternate forms of a gene (ex. Purple or white flower Alternate forms of a gene (ex. Purple or white flower color)color)
Dominant vs. RecessiveDominant vs. Recessive One allelic form “masks” the presence of anotherOne allelic form “masks” the presence of another ex. Purple flowers are dominant over white flowers ex. Purple flowers are dominant over white flowers
(white is recessive)(white is recessive) Dominant =capital lettersDominant =capital letters Recessive =lower case lettersRecessive =lower case letters
PPnn and F and Fnn
Parental and Filial generations Parental and Filial generations
More LingoMore Lingo Genotype vs. PhenotypeGenotype vs. Phenotype
Genotype is what alleles an individual has (ex. One purple flower Genotype is what alleles an individual has (ex. One purple flower allele and one white flower allele)allele and one white flower allele)
Phenotype is what the individual looks like (ex. Purple flowers)Phenotype is what the individual looks like (ex. Purple flowers) Homozygous vs. HeterozygousHomozygous vs. Heterozygous
Homo =sameHomo =same Hetero =differentHetero =different
True-breeding True-breeding Phenotype of parent is always seen in offspringPhenotype of parent is always seen in offspring The phenotype counterpart to the genotype term “homozygous”The phenotype counterpart to the genotype term “homozygous”
If an individual has a homozygous genotype, it will be true breedingIf an individual has a homozygous genotype, it will be true breeding Monohybrid vs. DihybridMonohybrid vs. Dihybrid
A monohybrid cross looks at just one trait in parents who are A monohybrid cross looks at just one trait in parents who are hybridshybrids
A dihybrid cross looks at more than one trait in parents who are A dihybrid cross looks at more than one trait in parents who are hybrids hybrids
Hybrid is another way of saying “heterozygous”Hybrid is another way of saying “heterozygous”
Monofactorial InheritanceMonofactorial Inheritance
A.k.a. Mendelian traitsA.k.a. Mendelian traits
Inheritance of a trait is determined by one Inheritance of a trait is determined by one genegene
Does not really existDoes not really exist Virtually all traits are affected to some degree Virtually all traits are affected to some degree
by other genes and by environmental factorsby other genes and by environmental factors
The Gene for Stem LengthThe Gene for Stem Length
The tall allele is dominant (T)The tall allele is dominant (T) A true-breeding tall plant is homozygous A true-breeding tall plant is homozygous
dominant (TT)dominant (TT)
The short allele is recessive (t)The short allele is recessive (t) A true-breeding short plant is homozygous A true-breeding short plant is homozygous
recessive (tt)recessive (tt)
Homozygous (True-breeding) Homozygous (True-breeding) DominantDominant
Tall plant X Tall plantTall plant X Tall plant
XX
All offspring will be tall
Homozygous (True-breeding) Homozygous (True-breeding) RecessiveRecessive
Short stem plant X Short stem plantShort stem plant X Short stem plant
XX
All offspring will be short
Non-True-BreedingNon-True-Breeding
Tall plant X Tall plantTall plant X Tall plant
XX
Some offspring are tallSome offspring are short
??
Monohybrid Cross –Stem LengthParental generation (P1)
Tall X Short
(Both true-breeding)
F1
All Tall
(Non-true-breeding)
a.k.a. hybrids
F2
¼ Short ¾ Tall
True-breeding Tall
True-breeding Short
Non-true-breeding Tall
Mendel’s Law of SegregationMendel’s Law of Segregation Elementen separate into gametesElementen separate into gametes
We now know “elementen” as genesWe now know “elementen” as genes
Each individual carries 2 alleles for every geneEach individual carries 2 alleles for every gene One on each chromosome One on each chromosome
One allele on the chromosome from mom and one allele on the One allele on the chromosome from mom and one allele on the chromosome from dadchromosome from dad
Possibilities for any given genePossibilities for any given gene Homozygous Dominant (AA) (True breeding)Homozygous Dominant (AA) (True breeding) Heterozygous (Aa) (Non-true-breeding)Heterozygous (Aa) (Non-true-breeding) Homozygous Recessive (aa) (True-breeding)Homozygous Recessive (aa) (True-breeding)
Gametes carry just ONE allele for each geneGametes carry just ONE allele for each gene Possibilities are A or aPossibilities are A or a
The Punnett SquareThe Punnett Square
Used to determine phenotypic and genotypic ratiosUsed to determine phenotypic and genotypic ratios
Represents possible alleles in gametes and how Represents possible alleles in gametes and how gametes may combinegametes may combine
Probability of having an offspring with “tt” is the same (1/4) for every pregnancy/fertilization.
#s are ratios, not # of offspring
Dominant and Recessive TraitsDominant and Recessive Traits
A dominant trait requires only one allele in A dominant trait requires only one allele in order for the dominant trait to be order for the dominant trait to be expressed expressed
Flower color
White (p)
Purple (P)
There MUST be 2 recessive alleles There MUST be 2 recessive alleles present in order for a recessive trait to be present in order for a recessive trait to be expressed (phenotype)expressed (phenotype)
ExamplesExamples
Ex. 1: True-breeding (homozygous) recessive Ex. 1: True-breeding (homozygous) recessive
Ex. 2: Homozygous dominant X heterozygousEx. 2: Homozygous dominant X heterozygous
Ex. 3: Monohybrid (heterozygous) crossEx. 3: Monohybrid (heterozygous) cross
ExampleExample
Unknown X Homozygous RecessiveUnknown X Homozygous Recessive a.k.a “the test cross”a.k.a “the test cross”
Autosomes vs. Sex ChromosomesAutosomes vs. Sex Chromosomes
Autosomal traits are found on non-sex chromosomes so Autosomal traits are found on non-sex chromosomes so (they are not found on the X or Y sex chromosomes)(they are not found on the X or Y sex chromosomes)
Modes of InheritanceModes of Inheritance
Autosomal dominant inheritanceAutosomal dominant inheritance If a child exhibits the trait (phenotype) at least If a child exhibits the trait (phenotype) at least
one of the parents also exhibits the trait one of the parents also exhibits the trait (phenotype)(phenotype)
Autosomal recessive inheritanceAutosomal recessive inheritance Heterozygotes are carriers (genotype) and do Heterozygotes are carriers (genotype) and do
not exhibit the trait (phenotype)not exhibit the trait (phenotype)