Introduction to Genetics and Heredity

A. The Theory of Blending Inheritance• Each parent contributes factors that

blend in their offspring- ex. A short plant crossed with a tall plant would

produce a medium sized plant.

B. Gregor Mendel• Born in 1822 in Czech Republic• Worked as a teacher and performed

research on the heredity of pea plants

Although these dogs have similar

characteristics they

are each unique!

I. Early Ideas About Heredity

C. Mendel’s Experiment1. Procedure:

a. Cross-pollinate purebred pea plants

b. Use pea plants with different characteristics for the same trait- Traits include: seed shape and color, flower position, plant height etc.

C. Mendel’s Experiment2. Results:

a. The F1 (offspring) generation had the traits of only oneof the parents

b. The P1 (parental) generation’s traits did not blend

C. Mendel’s Experiment3. Conclusions:

a. Individual factors, which do not blend, control each trait of a living thing. These factors are called genes.

b. The different forms of a gene are called alleles.• For example, the gene for plant height

occurs in talland short form.

c. Some alleles are dominant, while others are recessive.C. The effects of a dominant allele are

seen even if a recessive allele is present.

D. The effects of a recessive allele are seen only if a dominant allele is not present.

A pair of chromosomes of DNA (each of these contain 1 chromatid--they have not duplicated). Gene (this one is made of 2 alleles and is heterozygous) Allele (this one is dominant)

Using a picture:

II. Using Genetic Vocabulary

A. Defining Terms:

1. DNA is organized into chromosomes. There are 23 pairs of

chromosomes (46 total) in all human cells except sex cells.

2. Genes are small segments of DNA present on chromosomes that

code for a particular protein. Multiple genes are found on one chromosome.

- The estimated # of genes in the human genome is around 30,000

3. Genes code for proteins, ultimately resulting in the expression of specific traits (characteristics).

II. Using Genetic Vocabulary Cont.

4. Genes come in different forms calledalleles. Alleles are either dominant (A) or recessive (a).

5. Organisms that have two identical alleles for a particular trait

are said to be homozygous (AA) or (aa).

6. Organisms that have two different alleles for the same trait are heterozygous (Aa).

7. The genotype (genetic make-up) for a particular trait determines

the phenotype (physical characteristic).A pair of chromosomes of DNA (each of these contain 1 chromatid--they have not duplicated). Gene (this one is made of 2 alleles and is heterozygous) Allele (this one is dominant)

Using a picture:

III. A Simple Example

The organisms in our fictional example have one pair of chromosomes per body cell. A gene on the chromosome codes

for either dark (D) or light (d) flower color.

Male: Female:

Genotype:

Phenotype:

dd

Homozygous recessive

Light flower color

DD

Homozygous dominant

Dark flower color

P1 (parental) Generation

To prepare for mating, special cells called gametes must form. The process used to make gametes is called meiosis. Gamete cells are haploid (containing only one homologous

chromosome per pair).

Male: Female:

P1 Generation

Pollen(sperm)

Note: 3 of the egg cells (polar bodies) will degenerate!

Ovule(egg)

d d DD

d d DD

When organisms “mate”, 1 sperm cell (or pollen grain) from dad will randomly combine with an egg cell (or ovule) from mom. These combined gametes will produce a diploid (2N)

offspring with a complete sets of chromosomes.

Male gamete:pollen or sperm

Female gamete:ovule or egg

d D

F1 (offspring) generation

Genotype: (gene coding for the flower color trait)

Phenotype:

Ddheterozygous

Dark flower color

In this example, all of the pollen cells contain the recessive allele (d) for flower color and the ovule cell

contains the dominant allele (D) for flower color

All offspring will be Dd with Darkflowers

Fertilization

The possible outcome of sexual reproductive genetic crosses can be seen using Punnett Squares:

Possible Female gametes:ovule or egg (result of Meiosis)

Possible Male gametes:pollen or sperm (result of Meiosis)

d

D

This is how to create a Punnett Square of the example we have just been discussing:

Possible offspring (F1 generation). In this case, 100% will be Dd with 100% Darkflowers

Dd Dd

Dd DdD

d

You will use Punnett Squares to determine the probability of offspring characteristics with different parental crosses.

P1 Generation