BASIC GENETICS

GENE: a unit of DNA that controls a trait of a particular organism (ex. Freckles) ALLELE: an alternative form a gene (one member of a pair) that is located at a specific position on a specific chromosome. Homologous Chromosomes Allele #1 Allele #2 Gene

DOMINANT allele An allele that can “mask over” a recessive allele. Only the dominant trait is expressed. It is generally represented by a CAPTIAL letter Ex. “B” RECESSIVE allele An allele that can only be expressed if a dominant allele is absent. It is generally represented by a LOWER CASE letter Ex. “b”

HOMOZYGOUS (purebred) A term used to describe a pair of alleles that are IDENTICAL or the SAME. Ex. BB or bb HETEROZYGOUS (hybrid) A term used to describe a pair of alleles that are DIFFERENT. Ex. Bb Homologous Chromosomes Gene Homologous Chromosomes Gene

GENOTYPE The description of the gene pair. Ex. BB, Bb, bb PHENOTYPE The observable trait that results from the action of an allele pair. Brown eyes blue eyes Ex. Brown eyes or blue eyes Genotype(s): Phenotype: Genotype: Phenotype:

H OW TO SET UP YOUR PUNNETT SQUARE 1. Read the word problem. Identify the dominant and recessive traits. 2. Make a key to represent the dominant and recessive alleles. 3. Determine the alleles of the parents. 4. Place the alleles of the parents along the top and left side of the punnett square. 5. Cross the alleles inside the boxes. 6. Determine the ratios of the offspring.

C ROSS A HOMOZYGOUS PURPLE FLOWER WITH A WHITE FLOWER. P URPLE IS DOMINANT TO WHITE. PHENOTYPIC RATIO: GENOTYPIC RATIO:

C ROSS TWO HETEROZYGOUS B ROWN HAIRED PARENTS. B ROWN IS D OMINANT TO B LONDE. PHENOTYPIC RATIO: GENOTYPIC RATIO:

A HETEROZYGOUS TALL PLANT IS CROSSED WITH A SHORT PLANT. T ALL IS D OMINANT TO S HORT. PHENOTYPIC RATIO: GENOTYPIC RATIO:

PEDIGREES

P EDIGREE ANALYSIS Male =Female = Marriage = Sibling = Fraternal Twins = Identical Twins = (Non-identical) Organization Rules: 1. Generations are numbered using Roman numerals, I, II, III, etc. 2. Children are placed in birth order starting from the left side.

PEDIGREE KEY = healthy = Tay Sacs

PEDIGREE KEY = brown eyes = blue eyes

The O’Connor Pedigree for Brown Hair KEY Brown Hair (B) = Blonde hair (b) =

I. II. III. KEY Immune to poison ivy (R) = Susceptible to poison ivy (r) = Family Pedigree for Poison Ivy Susceptibility

KEY Six-fingered (F) = Five-fingered (f) = Family Pedigree for Polydactly

COMPLEX GENETICS INCOMPLETE DOMINANCE

INCOMPLETE DOMINANCE: A type of inheritance when a heterozygous geneotype expresses a blending phenotype.

R= red W= white #1 Cross a snapdragon white flower with a pink flower.

R= red W= white #2 Cross a snapdragon pink flower with a pink flower.

C = curly hair S = straight hair #3 Cross a wavy haired person with a straight haired person.

COMPLEX GENETICS CO - DOMINANCE

Co-Dominance: Co-Dominance: 2 alleles are equally dominant and expressed. There are 3 alleles for blood typing: A, B, O A and B alleles are co-dominant O allele is recessive Even though “O” is capitalized, it is still considered a recessive allele. PHENOTYPE GENOTYPE “A” bloodAA, AO “B” bloodBB, BO “AB” bloodAB “O” bloodOO

#1 C ROSS A PERSON WITH HOMOZYGOUS “ A ” BLOOD AND A P ERSON WITH H OMOZYGOUS “B” BLOOD.

#2 C ROSS AN “O” BLOOD PERSON WITH A “AB” BLOOD PERSON.

#3 C ROSS A HETEROZYGOUS “A” BLOOD PERSON WITH A HETEROZYGOUS “B” BLOOD PERSON.

COMPLEX GENETICS SEX-LINKED

SEX-LINKED INHERITANCE A type of inheritance where certain alleles are found only on one sex chromosome (X) Color Blindness Werewolf Syndrome Hemophilia

TEST# 1 TEST# 2

R ED -G REEN C OLOR B LINDNESS

G REEN -Y ELLOW C OLOR B LINDNESS

B ASIC S EX D ETERMINATION P UNNETT S QUARE

PHENOTYPEGENOTYPE Normal FemaleXBXBXBXB X B X b (carrier) Abnormal FemaleXbXbXbXb Normal MaleXBYXBY Abnormal MaleXbYXbY

#1 C ROSS A COLORBLIND M ALE WITH A N ORMAL F EMALE.

#2 C ROSS A COLORBLIND M ALE WITH A N ORMAL F EMALE CARRIER.

KEY Normal = Colorblind =