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Home , Allele

3 (CH 7)

Dr. Terence Lee

Genetics

Genetics

1 2.20 DNA holds the genetic information to build an organism.

2.21 RNA is a universal translator, reading DNA and directing protein production.

2 Genetics

INHERITANCE OF

Maternal Paternal Humans have pair chromosome pair 23 pairs of (46 individual chromosomes) and, thus, two copies of each gene.

Maternal gamete: egg Paternal gamete: sperm Each human gamete has just one copy of each chromosome and, thus, one copy of each gene.

Gametes unite during fertilization.

Child inherits one set of chromosomes from each parent and, thus, two copies of each gene.

FISH SYNDROME

Egg Sperm Normal version Defective version of of FMO3 the FMO3 gene, gene responsible for fish odor syndrome

Gametes unite during fertilization.

Genes for FMO3 Child inherits one copy of the defective version of the FMO3 gene. The child is a “silent carrier” and will not have fish odor syndrome.

If two copies of the defective version of FMO3 were present, the child would develop fish odor syndrome.

3 Genetics

• Alleles are found on homologous chromosomes. • Homologous Chromosomes

Homologous Chromosomes

4 vs.

• The genotype of an organism describes the combination of alleles present.

• Example: earlobes –E = allele for free earlobe – e = allele for attached earlobe • Three combinations in diploid : – EE, ee, and Ee

These are genotypes These are phenotypes

Genotypes vs. Phenotypes

Allele Symbols Genotype Phenotype •E = free •e = attached EE Free earlobes Ee Free earlobes ee Attached earlobes

• How do the genotypes determine the phenotype?

5 Dominant vs. Recessive

Genotype Phenotype

Allele Symbols EE Free earlobes •E = dominant •e = recessive Ee Free earlobes ee Attached earlobes

• The dominant allele masks the recessive allele in the phenotype • The recessive allele only manifests in the absence of the dominant allele

More on Alleles

Genotype Phenotype

Homozygous dominant EE Free earlobes Heterozygous Ee Free earlobes

Homozygous ee Attached earlobes recessive • Homozygous refers to the genotype having two identical alleles for a trait. • Heterozygous refers to the genotype having different alleles for a trait.

Punnett Square

Ee x Ee EE x EE ee x ee

E e EE e e E EEEe E EEEE e ee ee e Ee ee E EEEE e ee ee

6 Fertilization

Genotype Gamete Genotype Probability (diploid) (haploid) EE E E=100% Ee E or e E=50%, e=50% ee e e=100%

• The Law of Segregation

Fertilization Gametes from One parent E e

E EEEe Possible Offspring e Ee ee Genotypes

Gametes from other parent

What are the possible outcomes if Ee and Ee were mated?

Fertilization

Offspring: E e •25% are EE •50% are Ee E EE Ee •25% are ee e Ee ee

7 History of DNA

• did not know about DNA. • He was still able to study inheritance using the plant.

DOMINANT AND RECESSIVE TRAITS

1 Mendel crossed true-breeding purple-flower plants with true- breeding - flower plants.

True-breeding True-breeding purple-flower plant white-flower plant

The purple-colored All offspring have purple flowers. flower is the dominant trait, while the white- colored flower is a recessive trait.

2 Then, Mendel crossed two of the purple-flower offspring.

8 DOMINANT AND RECESSIVE TRAITS

The purple-colored All offspring have purple flowers. flower is the dominant trait, while the white- colored flower is a recessive trait.

2 Then, Mendel crossed two of the purple- flower offspring.

Most offspring have purple flowers, but some have white flowers.

The recessive trait for the white-colored  flower must have been lurking in the previous generation, even though it is not visible.

Mendelian Genetics

• Example: Purple and White flowers

Possible Genotypes Phenotype Possible Sex Cells PP = homozygous Purple 100% P Pp = heterozygous Purple 50% P, 50% p pp = homozygous white 100% p

Allele Symbols •P = Purple •p = white

Mendelian Genetics

PP Generation Genotype

p Pp Pp P0 Parent PP x pp

p Pp Pp F1 Offspring Pp

• Mendel’s First Cross – Cross pure bred with pure bred – Homozygous purple x homozygous white

9 Mendelian Genetics

• Mendel’s First Cross F 1 – Genotype PP • 100% Pp – Phenotype p Pp Pp • 100% Purple p Pp Pp

Allele Symbols •P = Purple •p = white

Mendelian Genetics

• Mendel’s Second Cross – Cross F1 with each other P p –Pp x P p P PPPp • Results for F 2 – Genotype p Pp Pp • 25% PP • 50% Pp Allele Symbols • 25% pp •P = Purple – Phenotype •p = white • 75% purple • 25% white

Mendelian Genetics

• Mendel’s crossing experiment demonstrates two things: 1. Law of – dominant allele masks the recessive allele 2. Law of Segregation – alleles retain their individuality in diploid organisms by separating and moving to different gametes

No blending

10 : A Punnett square is a useful tool for determining the possible outcomes of a cross between two individuals.

MOTHER albino Cross 1 homozygous aa

GAMETES a a FATHER pigmented homozygous AA A

Aa Aa GAMETES

A

Aa Aa

OFFSPRING Genotype Phenotype All heterozygous Aa All pigmented

MOTHER pigmented Cross 2 heterozygous Aa

GAMETES A a FATHER pigmented heterozygous Aa A

AA Aa GAMETES

a

Aa aa

OFFSPRING Genotype Phenotype 1/4 homozygous dominant AA 3/4 pigmented 2/4 heterozygous Aa

1/4 homozygous recessive aa 1/4 albino

GENETICS AND PROBABILITY

IF… The mother is albino, and the father is heterozygous

THEN… aa Aa There is a 100% chance that 100% 50% the mother’s egg will carry the recessive a allele and a 50% chance that a sperm will carry the recessive a allele a a A a

AND… 1.0× 0.5 = 0.5 or 50% chance the Multiply the two components together offspring will to determine the overall probability. be albino. aa

11 TAY-SACHS AND PROBABILITY

IF… Parents are heterozygous for Tay-Sachs

Tt Tt THEN… 50% 50% There is a 50% chance that a gamete will carry the recessive t allele

T t T t

AND… 0.5 × 0.5 = 0.25 or 25% chance the child will be Multiply the two components together homozygous for Tay-Sachs. to determine the overall probability. tt

PEDIGREE

A pedigree is a useful tool to document a trait of interest across multiple generations of family members.

Grandfather Grandmother Grandfather Grandmother

Aunt Uncle Father Mother Uncle Aunt

First First Sister Me Sister cousin cousin Female exhibiting trait of interest Female not exhibiting trait Male exhibiting trait of interest Male not exhibiting trait

Incomplete Dominance

• Incomplete dominance is when the heterozygote is an intermediate between the two homozygotes and appears to be blended.

12 INCOMPLETE DOMINANCE: SNAPDRAGONS Incomplete dominance occurs when a heterozygote exhibits an intermediate phenotype between the two homozygotes.

The superscript W represents the allele that produces no pigment (white MOTHER flower). The superscript R represents the white-flower allele that produces pigment homozygous (red flower). Cross 1 CWCW

GAMETES CW CW FATHER red-flower homozygous CRCR CR

CWCR CWCR GAMETES

CR

CWCR CWCR

OFFSPRING Genotype Phenotype

All heterozygous CWCR All pink flowers

INCOMPLETE DOMINANCE: SNAPDRAGONS

MOTHER pink-flower heterozygous Cross 2 CWCR

CW GAMETES CR FATHER pink-flower heterozygous CWCR CW

CWCW CWCR GAMETES CR

CWCR CRCR OFFSPRING Genotype Phenotype

1/4 homozygous CRCR 1/4 red flowers

2/4 heterozygous CWCR 2/4 red flowers

1/4 homozygous CWCW 1/4 white flowers

Co-dominance

• In codominance , both alleles are expressed in the heterozygote. – Example: coat color.

13 is an example of Co-dominance .

BLOOD TYPE, ANTIGENS, AND ANTIBODIES Antigens are Type A Type B Type AB Type O chemicals on the surface of some cells. B antigens Neither A They act as signposts A antigens A and B nor B that tell the immune antigens antigens system whether the cell belongs in the body. Antibodies are B antibodies A antibodies A and B immune system Neither A nor B antibodies antibodies molecules that attack cells with foreign antigens.

Law of Independent Assortment

• The Law of Independent Assortment states that alleles of one characteristic separate independently of the alleles of another.

Law of Independent Assortment

• Example: earlobes and hair color – Must be genes on different chromosomes.

Genotypes Phenotype Genotype Phenotype EE Free earlobe HH Dark hair Ee Free earlobe Hh Dark hair ee Attached earlobe hh Light hair

E = free earlobe, e = attached earlobe H = dark hair, h = light hair

14 Law of Independent Assortment

• Example: – The father and mother both have free earlobes and dark hair – What are the possible offspring genotypes and phenotypes when two heterozygous parents are crossed?

Law of Independent Assortment

• What are the genotypes of the heterozygous parents? – Phenotype – free earlobes and dark hair – Genotype – Ee and Hh or EeHh – Cross two heterozygous parents: • EeHh x EeHh

Law of Independent Assortment

EH EH Eh Eh eH eH eh eh

• What are the possible gametes from EeHh x EeHh ?

15 Law of Independent Assortment

• Setup the Punnett Square for EeHh x EeHh

EH Eh eH eh EH EEHH EEHh EeHH EeHh Eh EEH h EEHh EeH h Eehh eH EeH HEeH h eeHH eeHh eh EeHh Eeh h eeH h eehh

Law of Independent Assortment

genotype Free Earlobes and Free Earlobes and Attached Earlobes Attached Earlobes Dark Hair Light Hair and Dark Hair and Light Hair

1 – EEHH 1 – EEhh 1 – eeHH 1 – eehh 2 – EEHh 2 – Eehh 2 – eeHh 2 – EeHH 4 - EeHh 9/16 3/16 3/16 1/16

Phenotype

16