Semester 2 Final Review Part 1

Genetics, Biotechnology, Protein Synthesis and Evolution

We’ve all heard of it, but … What is genetics?

Genetics: the study of gene structure and action and the patterns of inheritance of traits from

parent to offspring.

Mendel’s experiments

Mendel’s Principle Findings• Dominant and Recessive –Certain characteristics are dominant to

others – The dominant trait will mask another

(recessive) trait, preventing it’s expression– The recessive trait “disappears” for a

generation

Cross between varieties

The dominant trait will mask another (recessive) trait,

preventing it’s expression

• Segregation – For each trait, organisms have 2 genes

– Each pea plant got one gene from each parent – Genes segregate from each other during egg or

sperm formation (meiosis)

Mendel’s Principle Findings

Some terms …

• Trait: characteristics of an organism pass from generation to generation.– Eye color– Hair color and type– Height– Temperament– Symptoms for genetic diseases

Genotype

• Tells you the genetic makeup of the organism • The genes the organism carries

• Written using symbols – Each allele is represented by a letter • Tall = T dominant • Short = t recessive

– Capital letter designates the dominant trait and lower case letter designates the recessive trait.

– Capital letter is always written first.

Homozygous

• An individual which contains one allele for a genetic trait

– TT-- homozygous dominant – tt -- homozygous recessive

Heterozygous

• An individual which contains different alleles for a genetic trait– Tt heterozygote

Phenotype

• What the organism looks like

• Controlled by the genotype – TT---------- tall – Tt----------- tall – tt------------ short

Example

eye color geneAllele b(blue eyes)

eye color geneAllele B (brown eyes)

Paternal Maternal

This person would have brown eyes (Bb)

Phenotype

Genotype

Punnett squares

• The probability the next generation will exhibit a certain trait can be shown with a punnett square.

• The genotype of the mother is shown on the top of the square

(TT)• The genotype of the father is shown on the side of the square

(tt)• The various combinations of genes (genotypes) are shown in the squares. All of these offspring will be (T) Tall and carry the recessive (t) short allele.

Tt Tt

Tt Tt

T T

t

t

• What happens if you cross a heterozygous plant (Tt) with a short plant (tt)?

Punnett squares

T t

t Tt tt

t Tt tt

Two of the four will be Heterozygous (Tall) and the other two will be homozygous recessive (short)

This is a 1:1 ratio

Monohybrid vs. Dihybrid

• Monohybrid crosses are crosses that examine the inheritance of only one specific trait.

• Dihybrid crosses are crosses that examine the inheritance of two different traits.

Mendel and Dihybrid Crosses

• Mendel studied dihybrid crosses.– He crossed a plant with yellow round peas with a

plant with green wrinkled peas.

Mendel and Dihybrid Crosses

• Mendel began his experiments with purebred (homozygous) parent plants. RRYY x rryy– Remember each trait has 2 genes due to getting

half your genes from mom and half from dad. • How many gamete options do you have for RRYY??

RY

rryy? ry

• These are the gametes from the “P” generation.

Mendel and Dihybrid Crosses“P” generation: RRYY x rryy

RRYY

rryy

RY RY RY RYry RrYy RrYy RrYy RrYyry RrYy RrYy RrYy RrYyry RrYy RrYy RrYy RrYyry RrYy RrYy RrYy RrYy

Mendel and Dihybrid CrossesWhat is the genotypic ratio? 16 RrYy:0 anything elsePhenotypic ratio? 16 Round Yellow: 0 anything else

RY RY RY RYry RrYy RrYy RrYy RrYyry RrYy RrYy RrYy RrYyry RrYy RrYy RrYy RrYyry RrYy RrYy RrYy RrYy

Mendel and Dihybrid CrossesHe then crossed two “F1” organisms: RrYy x RrYy

RY Ry rY ryRY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy RryyrY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

RrYy

RrYy

Mendel and Dihybrid Crosses

What is the genotypic ratio for the F2 generation? 1 RRYY:2 RRYy: 2 RrYY: 4 RrYy: 1 rrYY: 2 Rryy: 2 rrYy: 1rryy: 1 RRyy

RY Ry rY ryRY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy RryyrY RrYY RrYy rrYY rrYyry RrYy Rryy rrYy rryy

Mendel and Dihybrid Crosses

Phenotypic ratio for the F2 generation?

RY Ry rY ryRY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy RryyrY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

9:16 Round Yellow,3:16 Round Green, 3:16 Wrinkled Yellow, 1:16 Wrinkled Green

Mendel and Dihybrid Crosses

9:16 yellow and round,3:16 green and round,3:16 wrinkled and yellow,1:16 wrinkled and green.

Genetics VocabularyGene Law of SegregationDominant Law of Independent AssortmentRecessive Genotype:

Homozygous DominantP Generation Homozygous RecessiveF1 Generation HeterozygousF2 Generation PhenotypeTrait Punnett SquareAllele Monohybrid Cross

Dihybrid Cross