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 alleleAn 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 alleleAn 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. BbHomologous 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.

Ex. Brown eyes Brown eyes or blue eyesblue eyes

Genotype(s):

Phenotype:

Genotype:

Phenotype:

HOW 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.

CROSS A HOMOZYGOUS PURPLE FLOWER WITH A WHITE FLOWER. PURPLE IS DOMINANT TO WHITE.

PHENOTYPIC RATIO:

GENOTYPIC RATIO:

CROSS TWO HETEROZYGOUS BROWN HAIRED PARENTS. BROWN IS DOMINANT TO BLONDE.

PHENOTYPIC RATIO:

GENOTYPIC RATIO:

A HETEROZYGOUS TALL PLANT IS CROSSED WITH A SHORT PLANT. TALL IS DOMINANT TO SHORT.

PHENOTYPIC RATIO:

GENOTYPIC RATIO:

PEDIGREES

PEDIGREE 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.

PEDIGREEKEY = healthy

= Tay Sacs

PEDIGREEKEY = brown eyes

= blue eyes

The O’Connor Pedigree for Brown HairKEY

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

COMPLEXGENETICS

INCOMPLETE DOMINANCE

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

R= redW= white

#1 Cross a snapdragon white flower with a pink flower.

R= redW= white

#2 Cross a snapdragon pink flower with a pink flower.

C = curly hairS = straight hair

#3 Cross a wavy haired person with a straight haired person.

COMPLEXGENETICS

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” blood AA, AO

“B” blood BB, BO

“AB” blood AB

“O” blood OO

#1 CROSS A PERSON WITH HOMOZYGOUS “A” BLOOD AND A PERSON WITH HOMOZYGOUS “B” BLOOD.

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

#3 CROSS A HETEROZYGOUS “A” BLOOD PERSON WITH A HETEROZYGOUS “B” BLOOD PERSON.

COMPLEXGENETICS

SEX-LINKED

SEX-LINKED INHERITANCEA type of inheritance where certain alleles are

found only on one sex chromosome (X)

Color Blindness

Werewolf Syndrome

Hemophilia

TEST# 1TEST# 2

RED-GREEN COLOR BLINDNESS

GREEN-YELLOW COLOR BLINDNESS

BASIC SEX DETERMINATION PUNNETT SQUARE

PHENOTYPE GENOTYPE

Normal Female XBXB

Normal Female XBXb (carrier)

Abnormal Female XbXb

Normal Male XBY

Abnormal Male XbY

#1 CROSS A COLORBLIND MALE WITH A NORMAL FEMALE.

#2 CROSS A COLORBLIND MALE WITH A NORMAL FEMALE CARRIER.

KEY

Normal =

Colorblind =