GeneticsGenetics

Chapter 11Chapter 11

Gregor MendelGregor Mendel

““Father” of geneticsFather” of genetics Austrian monk, mid-1800sAustrian monk, mid-1800s Researched pea plant inheritanceResearched pea plant inheritance

– Easy to grow, fast reproductionEasy to grow, fast reproduction– Studied plant height, pea shape/color, Studied plant height, pea shape/color,

pod color, etc.pod color, etc.

Pea Plant ReproductionPea Plant Reproduction

Self-pollinationSelf-pollination– Male gametes (pollen) fertilize egg of Male gametes (pollen) fertilize egg of

same flowersame flower– Produces pure-bred offspringProduces pure-bred offspring– True-breeding: produce offspring True-breeding: produce offspring

identical to parent when self-pollinatedidentical to parent when self-pollinated

Pea Plant ReproductionPea Plant Reproduction

Cross-pollinationCross-pollination– Pollen from one plant fertilizes egg of Pollen from one plant fertilizes egg of

another plantanother plant– Offspring have two parentsOffspring have two parents

Mendel’s ExperimentsMendel’s Experiments

P = Parent generationP = Parent generation FF11 = First filial generation = First filial generation

FF22 = Second filial generation (F = Second filial generation (F11 X F X F11))

PP Pure Green X Pure Yellow Pure Green X Pure Yellow

FF11 All GreenAll Green

FF22 3 Green:1 Yellow3 Green:1 Yellow

Mendel’s ConclusionsMendel’s Conclusions

Law of Dominance – one allele (form Law of Dominance – one allele (form of a gene) is dominant, one is of a gene) is dominant, one is recessiverecessive– Recessive trait was hidden in FRecessive trait was hidden in F11

generationgeneration– Green = dominantGreen = dominant– Yellow = recessiveYellow = recessive

Mendel’s ConclusionsMendel’s Conclusions

Law of Segregation: Law of Segregation: alleles for a gene alleles for a gene separate when separate when gametes form gametes form (meiosis I)(meiosis I)– Each gamete gets Each gamete gets

one copy of each one copy of each genegene

Some Vocab.Some Vocab.

Genotype – allele combinationGenotype – allele combination– Capital letter = dominant alleleCapital letter = dominant allele– Lowercase letter = recessive alleleLowercase letter = recessive allele– Ex – AA, Aa, aaEx – AA, Aa, aa

Phenotype – physical appearancePhenotype – physical appearance– Ex – green, yellowEx – green, yellow

Some Vocab.Some Vocab.

Homozygous – two alleles sameHomozygous – two alleles same– Homozygous dominant: AAHomozygous dominant: AA– Homozygous recessive: aaHomozygous recessive: aa

Heterozygous – two alleles differentHeterozygous – two alleles different– AaAa

Punnett SquaresPunnett Squares

First must determine possible First must determine possible gametesgametes

Heterozygous tall plant = TtHeterozygous tall plant = Tt– Half of gametes will get ‘T’, other half Half of gametes will get ‘T’, other half

will get ‘t’will get ‘t’ Homozygous tall plant = TTHomozygous tall plant = TT

– All gametes will get ‘T’All gametes will get ‘T’

Punnett SquaresPunnett Squares

Monohybrid crossMonohybrid cross– Cross involving one Cross involving one

traittrait Gametes go on the Gametes go on the

top and sidetop and side Combine gametes Combine gametes

to find possible to find possible offspringoffspring

Tt X Tt

Punnett SquaresPunnett Squares

Genotype ratioGenotype ratio

1TT: 2Tt: 1tt1TT: 2Tt: 1tt

Phenotype ratioPhenotype ratio

3 tall: 1 short3 tall: 1 short

Tt X Tt

ProbabilityProbability

Punnett squares are used to predict Punnett squares are used to predict the probability of certain traits in the probability of certain traits in offspring of genetic crossesoffspring of genetic crosses

Tt X TtTt X Tt– ½ chance of getting ‘t’ from mom, ½ ½ chance of getting ‘t’ from mom, ½

chance of getting ‘t’ from dadchance of getting ‘t’ from dad– ½ X ½ = ¼ tt in offspring½ X ½ = ¼ tt in offspring

Dihybrid CrossDihybrid Cross

Mendel looked at the inheritance patterns Mendel looked at the inheritance patterns of two traitsof two traits– Seed shape and seed colorSeed shape and seed color

Found that the traits were inherited Found that the traits were inherited independently of each otherindependently of each other

Law of Independent AssortmentLaw of Independent Assortment– Genes on separate chromosomes are inherited Genes on separate chromosomes are inherited

at randomat random– Due to random chromosome shuffling in Due to random chromosome shuffling in

Metaphase IMetaphase I

Independent AssortmentIndependent Assortment

Metaphase I

Non-Mendelian GeneticsNon-Mendelian Genetics

Not all traits follow Mendel’s Law of Not all traits follow Mendel’s Law of DominanceDominance

Four VariationsFour Variations– Incomplete Dominance (blending)Incomplete Dominance (blending)– Codominance (two phenotypes)Codominance (two phenotypes)– Multiple AllelesMultiple Alleles– Polygenic TraitsPolygenic Traits

Incomplete DominanceIncomplete Dominance

Neither allele is dominant, both Neither allele is dominant, both produce a proteinproduce a protein

Heterozygous phenotype is a blend Heterozygous phenotype is a blend of both homozygous phenotypesof both homozygous phenotypes

Ex – wavy hair, pink flowersEx – wavy hair, pink flowers

Incomplete DominanceIncomplete Dominance

CodominanceCodominance

Neither allele dominates the other, Neither allele dominates the other, both produce a proteinboth produce a protein

Heterozygous phenotype is a Heterozygous phenotype is a combination of both homozygous combination of both homozygous phenotypesphenotypes

Ex – checkered chicken, human blood Ex – checkered chicken, human blood types, types,

Multiple AllelesMultiple Alleles

Some genes have more than two Some genes have more than two allelesalleles

Each individual only gets two, but Each individual only gets two, but there are more than two in the there are more than two in the populationpopulation

Ex – Rabbit fur colorEx – Rabbit fur color

Multiple AllelesMultiple Alleles

Rabbit fur alleles (in order of Rabbit fur alleles (in order of dominance)dominance)– C: dark grayC: dark gray– ccchch: chinchilla: chinchilla– cchh: himalayan: himalayan– c: albinoc: albino

Multiple AllelesMultiple Alleles

Polygenic TraitsPolygenic Traits

Many traits are Many traits are controlled by more controlled by more than one genethan one gene

Traits show wide Traits show wide variationvariation

Ex – human height, Ex – human height, IQ, bell pepper IQ, bell pepper colorscolors