GENETICS AND HEREDITY Genes found on chromosomes in

the nucleus of a cell, code for the inherited characteristics we call traits

The passing of traits from parents to offspring is known as heredity

The scientific study of heredity is called genetics

Lacking today’s technology the first studies of genetics were based on physical appearance and mathematics

GREGOR MENDEL

Mendel was an Austrian monk who loved gardening and mathematics

He designed simple experiments with pea plants to determine how heritable traits were transferred from one generation to the next

MENDEL’S PEA TRAITS

MENDEL’S CONCLUSIONS1. Each trait is controlled by two genes that

they receive from their parents

2. Some genes are dominant over others (shown in capital letters)

3. Genes that are masked by dominant genes are called recessive genes (shown in lower case letters)

4. The combination of these two genes determines the traits offspring will exhibit

5. How often these traits will appear is predictable

TERMINOLOGY

GENOTYPE -

PHENOTYPE -

PUREBRED (homozygous) -

HYBRID (heterozygous) -

REGINALD PUNNETT

Based on the work of Mendel, he developed the “Punnett Square” as a method of predicting the results of a genetic cross (breeding)

Dominant genes are -

Recessive genes are -

CROSS #1Tall purebred pea plant (TT)

x

Short purebred pea plant (tt)

Tall (T) dominant

Short (t) recessive

RESULT:

-

GENOTYPE BOX

PHENOTYPE BOX

t t

T

T

- -

- -

CROSS #2Tall hybrid pea plant (Tt)

x

Tall hybrid pea plant (Tt)

Tall (T) dominant

Short (t) recessive

RESULT:

-

-

-

GENOTYPE BOX

PHENOTYPE BOX

T t

T

t

- -

- -

Principles of Genetics1. -

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