Mendelian Genetics The Basics

Gregor Mendel??? Known as the Father of Genetics: His experiments with Pea plants from began our understanding of how traits, things like hair or eye color, height, weight, ect……., were passed down from generation to generation. Known as the Father of Genetics: His experiments with Pea plants from began our understanding of how traits, things like hair or eye color, height, weight, ect……., were passed down from generation to generation. He came up with the principles of heredity that still hold true today by studying 7 characteristics of peas in his garden. He came up with the principles of heredity that still hold true today by studying 7 characteristics of peas in his garden. His work started and formed the base of all genetics, a field we learn more about every day. His work started and formed the base of all genetics, a field we learn more about every day.

How did He do it Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. He got true breeders by allowing self pollination. He got true breeders by allowing self pollination. The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation. The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation. Mendel allowed the F 1 hybrids to self-pollinate to produce an F 2 generation. Here he came up with his 2 famous laws of segregation and independent assortment. Mendel allowed the F 1 hybrids to self-pollinate to produce an F 2 generation. Here he came up with his 2 famous laws of segregation and independent 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. Dominate genes always show and ‘dominate’. Recessive genes can hide, and only show when no dominate genes are present

The Law of Segregation 1. different version of genes (alleles) account for variations in inherited characters or traits 1. different version of genes (alleles) account for variations in inherited characters or traits Ex Blue and Brown eyes, both eye color genes just different versions Ex Blue and Brown eyes, both eye color genes just different versions 2. For each trait, organisms inherit 2 alleles, one from each parent. 2. For each trait, organisms inherit 2 alleles, one from each parent.

The Law of Segregation 3. If two alleles differ, then one, the dominant allele, is fully expressed while the other, Recessive, is masked or only partially shown (ie if you get an allele for brown eyes from your mom and an allele of blue eyes from you dad, the dominate gene (Brown) is the colour of your eyes. 3. If two alleles differ, then one, the dominant allele, is fully expressed while the other, Recessive, is masked or only partially shown (ie if you get an allele for brown eyes from your mom and an allele of blue eyes from you dad, the dominate gene (Brown) is the colour of your eyes.

Dominate alleles are capitalized, while recessive genes are non capitals Dominate alleles are capitalized, while recessive genes are non capitals Ie Ie B- Brown eyes (dominate) B- Brown eyes (dominate) b – blue eyes (recessive) b – blue eyes (recessive) E – attached earlobes (dominate) E – attached earlobes (dominate) e – unattached earlobes (recessive) e – unattached earlobes (recessive)

Punnett Square Predictions be.com/watch?v= V_pl5lcSUFg be.com/watch?v= V_pl5lcSUFg be.com/watch?v= V_pl5lcSUFg be.com/watch?v= V_pl5lcSUFg

Genetics Vocabulary organism with two identical alleles for a trait is homozygous. ( TT or tt) Big letters= Dominant small or lower case = recessive. organism with two identical alleles for a trait is homozygous. ( TT or tt) Big letters= Dominant small or lower case = recessive. Organisms with two different alleles for a character is heterozygous ( Tt or Pp) Organisms with two different alleles for a character is heterozygous ( Tt or Pp) _humans _humans _humans _humans

Genetics Vocabulary description of an organism’s traits is its phenotype Ex) What it looks like, tall, short,white, black ect…. description of an organism’s traits is its phenotype Ex) What it looks like, tall, short,white, black ect…. description of its genetic makeup is its genotype. Ex) description of its genetic makeup is its genotype. Ex) Homozygous brown eyes BB Genotype – BB Phenotype – Brown Eyes Heterozygous brown eyes Bb Heterozygous brown eyes Bb Genotype ___, Phenotype ___

Test Cross Tales the Tale

Sound Simple Right???? The relationship of genotype to phenotype is rarely simple like in our examples because there are exceptions to all rules. The relationship of genotype to phenotype is rarely simple like in our examples because there are exceptions to all rules. Mendel lucked out in picking peas plants because each trait is controlled by 1 gene, genetically simple. But this is rare…. Mendel lucked out in picking peas plants because each trait is controlled by 1 gene, genetically simple. But this is rare…. some alleles show incomplete dominance where heterozygotes show a distinct intermediate phenotype, not seen in homozygotes. some alleles show incomplete dominance where heterozygotes show a distinct intermediate phenotype, not seen in homozygotes. Snapdragons and roses are Snapdragons and roses are good examples good examples

Snapdragons

Codominance codominance 2 alleles affect the phenotype in separate, distinguishable ways codominance 2 alleles affect the phenotype in separate, 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 multiple allele gene have 3 alleles present. A,B,O Ex. Is blood type. DRAW. This is also multiple allele gene have 3 alleles present. A,B,O Fact: Just because an allele is dominant does not make it more prevalent in a population. Fact: Just because an allele is dominant does not make it more prevalent in a population. Ex. Polydactyl is dominant to having the normal 5 fingers and toes but 399 out of 400 Ex. Polydactyl is dominant to having the normal 5 fingers and toes but 399 out of 400 have the recessive genes, what we call normal 5 and 5

Cont….. most genes are pleiotropic, affecting more than one phenotypic trait most genes are pleiotropic, affecting more than one phenotypic trait extensive symptoms of sickle-cell anemia are owed to a single gene. extensive symptoms of sickle-cell anemia are owed to a single gene. epistasis, a gene at one locus, or location, alters the phenotypic expression of a gene at a second locus epistasis, a gene at one locus, or location, alters the phenotypic expression of a gene at a second locus Ex. Mice and other mammals 1 gene determines if there is pigment in the hair C, there is, c, is not, and another determine color B,black or b, brown. Cc is albino Ex. Mice and other mammals 1 gene determines if there is pigment in the hair C, there is, c, is not, and another determine color B,black or b, brown. Cc is albino

Punnett Squares of Test Crosses Punnett Squares of Test Crosses Homozygo us Homozygo us recessive recessive a a a a A a Aa Aa aa aa Homozygous Homozygous recessive recessive a a a a A A Aa Aa Two phenotypes Two phenotypes All dominant phenotype All dominant phenotype

Genetic traits in humans can be tracked through family pedigrees Genetic traits in humans can be tracked through family pedigrees The inheritance of many human traits The inheritance of many human traits Follows Mendel’s laws Follows Mendel’s laws Dominant Traits Dominant Traits Recessive Traits Recessive Traits Freckles Freckles No freckles No freckles Widow’s peak Widow’s peak Straight hairline Straight hairline Free earlobe Free earlobe Attached earlobe Attached earlobe Figure 9.8 A Figure 9.8 A

Family pedigrees Family pedigrees Can be used to determine individual genotypes Can be used to determine individual genotypes Dd Dd Joshua Joshua Lambert Lambert Dd Dd Abigail Abigail Linnell Linnell D ? D ? John John Eddy Eddy D ? D ? Hepzibah Hepzibah Daggett Daggett D ? D ? Abigail Abigail Lambert Lambert dd dd Jonathan Jonathan Lambert Lambert Dd Dd Elizabeth Elizabeth Eddy Eddy Dd Dd dd Dd Dd Dd dd Dd Dd dd Dd Dd Dd dd Female Male Female Male Deaf Deaf Hearing Hearing Figure 9.8 B Figure 9.8 B

Parents Parents Offspring Offspring Sperm Sperm Norm al Norm al Dd Dd Norm al Norm al Dd Dd  Eggs Eggs D d DD DD Normal Normal Dd Dd Normal Normal (carrier) (carrier) Dd Dd Normal Normal (carrier) (carrier) dd dd Deaf Deaf Figure 9.9 A Figure 9.9 A Recessive Disorders Recessive Disorders Most human genetic disorders are recessive Most human genetic disorders are recessive