Mendelian Mendelian Genetics Genetics

The BasicsThe Basics

Gregor Mendel???Gregor Mendel??? Known as the Father of Genetics: His experiments Known as the Father of Genetics: His experiments

with Pea plants from 1856-1863 began our with Pea plants from 1856-1863 began our understanding of how traits, things like hair or eye understanding of how traits, things like hair or eye color, height, weight, ect……., were passed down color, height, weight, ect……., were passed down from generation to generation. from generation to generation.

He came up with the principles of heredity that still He came up with the principles of heredity that still hold true today by studying 7 characteristics of peas in hold true today by studying 7 characteristics of peas in his garden.his garden.

His work started and formed the base of all genetics, a His work started and formed the base of all genetics, a field we learn more about every day.field we learn more about every day.

IntroductionIntroduction Before Mendel it was the Blending Hypothesis which Before Mendel it was the Blending Hypothesis which

should give rise to a uniform population if true.should give rise to a uniform population if true. Mendel started the idea of particulate inheritance, Mendel started the idea of particulate inheritance,

which we use today.which we use today. Well it all started with just some pea, like Disney all Well it all started with just some pea, like Disney all

started with a mouse.started with a mouse. ???? WHY Peas???? WHY Peas

1. trait are in 2 very different forms, like flowers are 1. trait are in 2 very different forms, like flowers are either purple or white and seeds yellow or green either purple or white and seeds yellow or green and shape round or wrinkledand shape round or wrinkled

2. Male and female reproductive parts are 2. Male and female reproductive parts are contained in the same flower, you can control contained in the same flower, you can control matingmating

Cont…..Cont….. 3. 3. It is small It is small

and grows and grows easily and easily and quickly quickly producing producing many many offspring. offspring. All Good All Good ReasonsReasons

How did He do itHow did He do itMendel would cross-pollinate (Mendel would cross-pollinate (hybridizehybridize) two ) two

contrasting, true-breeding pea varietiescontrasting, true-breeding pea varieties..He got true breeders by allowing self pollinationHe got true breeders by allowing self pollination..The true-breeding parents are the The true-breeding parents are the P generationP generation

and their hybrid offspring are the and their hybrid offspring are the FF11 generation generation..

Mendel allowed the FMendel allowed the F11 hybrids to self-pollinate to hybrids to self-pollinate to

produce an Fproduce an F22 generation. Here he generation. Here he came up with his came up with his 2 famous laws of 2 famous laws of segregation and independent segregation and independent assortment. assortment.

•Mendel reasoned that the heritable factor for white flowers was present in the F1 plants, but it did not affect flower color.

•This is where dominant and recessive come in.

•He found a 3:1 ratio in many traits.

The Law of SegregationThe Law of Segregation11. different version of genes (. different version of genes (allelesalleles) account for ) account for

variations in inherited characters or traitsvariations in inherited characters or traits Alleles vary in their nucleotide sequences in genes. Ex Blue Alleles vary in their nucleotide sequences in genes. Ex Blue

and Brown eyes, both eye color genes just different versionsand Brown eyes, both eye color genes just different versions

2. For each trait, organisms inherit 2 alleles, one from 2. For each trait, organisms inherit 2 alleles, one from each parenteach parent..

3. If two alleles differ, then one, the 3. If two alleles differ, then one, the dominantdominant alleleallele, , is fully expressed while the other, is fully expressed while the other, RecessiveRecessive, is , is masked or only partially shown masked or only partially shown

4.4. The two alleles for each trait segregate during The two alleles for each trait segregate during gamete, sex cell, production. gamete, sex cell, production.

Hint:Hint: Mitosis and homologous chromosome separation Mitosis and homologous chromosome separation

Punnett Punnett Square Square

PredictionsPredictions

Genetics VocabularyGenetics Vocabulary organism with two identical alleles for a trait is organism with two identical alleles for a trait is

homozygous. ( TT or tt) homozygous. ( TT or tt) Big letters= Dominant small Big letters= Dominant small or lower case = recessive. or lower case = recessive.

Organisms with two different alleles for a character is Organisms with two different alleles for a character is heterozygous ( Tt or Pp)heterozygous ( Tt or Pp)

description of an organism’s traits is its description of an organism’s traits is its phenotypephenotype Ex) What it looks like, tall, short ,white, black ect….Ex) What it looks like, tall, short ,white, black ect….

description of its genetic makeup is its description of its genetic makeup is its genotype. Ex) genotype. Ex) Homo. D or R, Hetero. D or R.Homo. D or R, Hetero. D or R.

Test Cross Test Cross Tales the TaleTales the Tale

Law of Independent AssortmentLaw of Independent Assortment Used a dihybrid cross to figure this one out.Used a dihybrid cross to figure this one out. The Law states that the alleles of different genes The Law states that the alleles of different genes

separate independently of each other during separate independently of each other during gamete formationgamete formationpresence of one specific allele for one trait has no presence of one specific allele for one trait has no

impact on the presence of a specific allele for the impact on the presence of a specific allele for the second trait.second trait.

So one trait does not influence or control So one trait does not influence or control another. another. Not all dark haired people have dark Not all dark haired people have dark eyes.eyes. Ect…... Ect…...

Show probability just like dice and coin tossShow probability just like dice and coin toss

Sound Simple Right????Sound Simple Right???? The relationship of genotype to phenotype is rarely The relationship of genotype to phenotype is rarely

simple like in our examples because there are simple like in our examples because there are exceptions to all rules.exceptions to all rules.

Mendel lucked out in picking peas plants because Mendel lucked out in picking peas plants because each trait is controlled by 1 gene, genetically simple. each trait is controlled by 1 gene, genetically simple. But this is rare….But this is rare….

some alleles show some alleles show incomplete dominanceincomplete dominance where where heterozygotes show a distinct intermediate phenotype, heterozygotes show a distinct intermediate phenotype, not seen in homozygotes. not seen in homozygotes.

Snapdragons are good examples Snapdragons are good examples

SnapdragonsSnapdragons

Cont…….Cont……. codominancecodominance 2 alleles affect the phenotype in 2 alleles affect the phenotype in

separate, distinguishable waysseparate, distinguishable ways 2 dominant alleles expressed at the same time.2 dominant alleles expressed at the same time.

Ex. Is blood type. DRAW. This is also s multiple allele Ex. Is blood type. DRAW. This is also s multiple allele gene have 3 alleles present. A,B,Ogene have 3 alleles present. A,B,O

Fact: Just because an allele is dominant does not Fact: Just because an allele is dominant does not make it more prevalent in a population. make it more prevalent in a population. Ex. PolydactylEx. Polydactyl is dominant to having the normal 5 is dominant to having the normal 5

fingers and toes but 399 out of 400 have te fingers and toes but 399 out of 400 have te recessive what we call normal 5 and 5recessive what we call normal 5 and 5

Cont…..Cont….. most genes are most genes are pleiotropicpleiotropic, affecting more than one , affecting more than one

phenotypic traitphenotypic traitextensive symptoms of sickle-cell anemia are owed extensive symptoms of sickle-cell anemia are owed

to a single geneto a single gene.. epistasisepistasis, a gene at one locus, or location, alters the , a gene at one locus, or location, alters the

phenotypic expression of a gene at a second locusphenotypic expression of a gene at a second locusEx. Mice and other mammals 1 gene determines if Ex. Mice and other mammals 1 gene determines if

there is pigment in the hair C, there is, c, is not, and there is pigment in the hair C, there is, c, is not, and another determine color B,black or b, brown. Cc is another determine color B,black or b, brown. Cc is albinoalbino

Pleiotropic Pleiotropic

EpistasisEpistasis

Cont…….Cont……. polygenic inheritance,polygenic inheritance, the additive effects of 2 or the additive effects of 2 or

more genes on a single phenotypic trait. It can cause more genes on a single phenotypic trait. It can cause a great range in the phenotypic out come of an a great range in the phenotypic out come of an individual.individual.

Ex. Human skin color controlled by 3 genesEx. Human skin color controlled by 3 genes AABBCC individual is dark and aabbcc is lightAABBCC individual is dark and aabbcc is light crosses between two AaBbCc heterozygote crosses between two AaBbCc heterozygote

individuals would yield offspring covering a vast range individuals would yield offspring covering a vast range of shades. of shades. See pic..See pic..

Phenotype and EnvironmentPhenotype and Environment depends on environment and genes depends on environment and genes How Much of How Much of

each???????????????????????????each??????????????????????????? Ex. nutrition influences height and weight, exercise Ex. nutrition influences height and weight, exercise

alters build, sun-tanning darkens the skin, and alters build, sun-tanning darkens the skin, and experience improves performance on intelligence testsexperience improves performance on intelligence tests

ExEx. Hydrangea- Acid soil = blue flower and base= . Hydrangea- Acid soil = blue flower and base= pink. Genes are the same for both. pink. Genes are the same for both. Ex.Ex. Artic Fox turns Artic Fox turns brown in summer and white in winter so does snow brown in summer and white in winter so does snow shoe hair and grouse. shoe hair and grouse. ExEx. Fur color in Siamese cats . Fur color in Siamese cats influenced by temp. and so is influenced by temp. and so is Crotalus horridiusCrotalus horridius, Sex , Sex in many animals reptiles esp. is determined by temp. in many animals reptiles esp. is determined by temp. Ex. Identical twin diff. Use human examplesEx. Identical twin diff. Use human examples, , personality and height ect….personality and height ect….

ReferencesReferences

Jack Brown M.S. BiologyJack Brown M.S. BiologyStarr and Taggart: Starr and Taggart: The Unity and Diversity The Unity and Diversity

of Life 10th editionof Life 10th edition: 2004: Thomson : 2004: Thomson Brookes/ColeBrookes/Cole

Campbell and Reece: Campbell and Reece: Biology 6th editionBiology 6th edition. . Pg 1-23: 2002: Benjamin Cummings.Pg 1-23: 2002: Benjamin Cummings.

Microsoft Encarta Encyclopedia 2004Microsoft Encarta Encyclopedia 2004Raven and Johnson: Raven and Johnson: Holt BiologyHolt Biology: 2004: : 2004:

Holt, Rinehart and Winston. Holt, Rinehart and Winston.