Trait

Gene

Protein

Genes and Inheritance

Genes contain the information for the production of proteins, which specify traits.

Since genes are inherited, traits are also inherited.

Chromosome

Location of Genes

In sexually reproducing organisms, cells have a homologous pair of chromosomes (one from each parent).

Chromosomes from a homologous pair have the same genes but can have different alleles.

Allele: different form of a gene

May be dominant or recessive.

Chromosome from sperm(dad)

Chromosome from egg

(mom)

Homologous pair of chromosomes

Gregor Mendel: Father of Genetics

Genetics: branch of biology dealing with heredity

Gregor Mendel (1822-1884)was an Austrian monk who is regarded as the father of genetics.

Mendel used pea plants to study the inheritance patterns of many traits.

Mendel’s View of Inheritance

Parent A Parent B

Offspring

New Idea (Mendel)

Inherited traits behave as discrete units

Parent A Parent B

Offspring

Old IdeaBlending of

parental traits

Mendel’s Pea ExperimentsMendel examined a small number of phenotypic characters or traits in peas.

Dominant alleles masked recessive alleles.

Seed shape

round dominant over wrinkled

Seed color

yellow dominant over green

Pod shape

inflated dominant over constricted

Pod color

green dominant over yellow

Using a Punnett Square: Monohybrid Crosses

Calculates outcomes of genetic crosses.

Important vocabulary:

Homozygous dominant

Heterozygous

Homozygous recessive

Each parent provides

two gametes for the grid

Gametes

P

p

GametesP p

Parents

Pp Pp

X

Offspring

pp

PP Pp

Pp

Genotype and Phenotype

The genotype of an organism refers to its genetic make-up.

The phenotype of an organism refers to its observable features or traits.

pp(homozygous)

White

PP(homozygous)

Purple

Pp(heterozygous)

Purple

Pp(heterozygous)

Purple

Genotype Phenotype

Results of Mendel’s Experiments

Seed shape

Round Wrinkled

5474

1850

7324

RoundWrinkledTOTAL

2.96 : 1

Seed color

Yellow Green

6022

2001

8023

YellowGreenTOTAL

3.01 : 1

Pod color

Green Yellow

428

152

580

GreenYellowTOTAL

2.82 : 1

Flower position

Axial Terminal

651

207

858

AxialTerminalTOTAL

3.14 : 1

Pod shape

Inflated Constricted

882

299

1181

InflatedConstrictedTOTAL

2.95 : 1

Stem length

Tall Dwarf

787

277

1064

TallDwarfTOTAL

2.84 : 1

Mendel’s Law of Segregation

Each pair of alleles is separated into different gametes and into different offspring.

Gametes contain only one copy of a gene since they only receive one chromosome from each homologous pair.

Gametes (sperm Or egg cells)

Homologous pair of chromosomes, each has a copy of the gene on it (A or a)

aBaB

Gametes

AbAb

Intermediate Cells

Law of Independent Assortment

Alleles for different traits are sorted independently of each other.

All combinations of alleles are distributed to gametes with equal probability.

Genotype: AaBb

Polydactylism is a

dominant trait

Selected Hereditary TraitsDominant Recessive

Right handedness Left handedness

Hitch-hiker’s thumb Normal thumb

Polydactylism (extra digits) Normal digits

Pattern baldness Normal hair

Free ear lobes Attached ear lobes

Hitch-hiker’s thumbAttached ear lobe

Handedness

Free ear lobe

In this crowd of men, almost all

show some degree of pattern

baldness, a dominant trait.

Dominant

Human Tongue Roll

The ability to roll the tongue into a U-shape when viewed from the front is controlled by a dominant allele.

Recessive

Phenotype: Cannot roll tongue

Allele: t

Phenotype: Can roll tongue

Allele: T

Punnett Square Practice

1. Brown hair (B) is dominant over lighter hair

colors (b). If two heterozygotes for this trait

mate, what are the:

a. genotype frequencies

b. phenotype frequencies

of the offspring?

Punnett Square Practice

2. Dwarfism (D) is dominant over normal height (d).

If a person of normal height and a dwarf who is

homozygous dominant mate, what are the

chances of having a child that is also a dwarf?

Punnett Square Practice

3. Polydactyly, or having extra digits (P) is dominant over

having five digits on each limb (p). If a woman with

polydactyly mates with a normal male, then:

a. What are the possible genotypes of the woman?

b. What is the genotype of the male?

c. Create two Punnett Squares displaying their

possible children.

Punnett Square Practice

4. Tallness in pea plants (T) is dominant to

shortness (t). Round seeds (R) are dominant to

wrinkled seeds (r). Set up a Punnett Square

showing the mating results of two plants that are

heterozygous for both traits.