Classical Genetics

Species characteristics

Characteristics/traits shared by all individuals of a species

E.g. Presence of eyes, nose, arms etc. Of humans

Individual characteristics

Characteristics/traits that are unique/distinct to an individual of a species

E.g skin color on humans

Factors that affect individuality

Theory of blending inheritance Traits manifested on ofsspring are a

combination of the traits of the parents Heredity (nature) Environment (nurture)

Nature-Nurture Controversy

“Which is a more important factor in how your personality develops – nature or nurture?” What are the different factors that affect

individuality? How does heredity bring about traits in every

individual? How does environment affect an individual’s

traits?

Objectives

cite specific examples of each of the four types if hereditary characters

explain inheritance based on Mendelian laws

Hereditary Characters

Characters that are controlled by genes Genes ▪ factors of heredity▪ transmitted from one generation to the next

Which do you inherit from your parents?, the genes or the characters?

Hereditary Characters

Morphologic

al

Physiological

Behavioral Sexual

Hereditary Characters

Morphological Characters that

refer to structure or form such as shape, length or color of body parts

E.g. fur color in cats

hitchhiker’s thumb

bent little finger

Hereditary Characters

Physiological Characters that refer to the

functions of parts e.g. lactose intolerance and

diabetes mellitus

Hereditary Characters

Behavioral externally

directed activities in response to stimuli

examples are instincts such as crying and thumb sucking in babies

Hereditary Characters

Sexual Characters that

are associated with being male or female

E.g. moustache

Classifying Hereditary Characters

Classify the following and present your answer in tabulated form:

1. Hitchhiker’s thumb 8.Internal and external genitalia

2. Cleft chin 9. Spinning of spider’s web3. Bent little finger 10. Pubic hair4. Lactose intolerance 11. Diabetes mellitus5. Fur color in cats 12. Bird migration6. Widow’s peak 13. widening of hips in females7. Polydactyly 14. appearance of Adam’s

apples

Hereditary Characters

Morphological

Physiological

Behavioral

Sexual

Hereditary Characters

Morphological Hitchhiker’s thumb, bent little finger, cleft chin, fur color in cats, widow’s peak, polydactyly

Physiological Lactose intolerance, diabetes mellitus

Behavioral Spinning of spider’s web, bird migration

Sexual Pubic hair, internal and external genitalia, widening of hips in females, appearance of Adam’s apples

CLEFT CHIN

BENT LITTLE FINGER

SPINNING OF SPIDERS WEB

Mendel’s Experiments

Gregor Johann Mendel – Father of Classical Genetics Austrian monk and a botanist Joined the Augustinian Monastery of

St.Thomas at Brunn, Austria Spent 10 years in experimenting

garden peas (Pisum sativum) Another 2 years in analyzing the results

Why garden peas?

The plant has several characters that exhibit two contrasting expressions or traits.

The plant reproduces at a fast rate.

Garden peas can produce enough offspring for study purposes

Garden pea flowers are structurally adapted for self-pollination

Pollination can be controlled in this group of plants with minimum work

Mendel’s Experimental Design

1. Mendel studied one character with two contrasting expressions at a time, e.g. seed color, yellow and green.

yellow-seeded plants self-pollination pure-breeding yellow-seeded plants

green-seeded plants self-pollination pure-breeding green-seeded plants

2. Mendel cross-pollinated the two pure-breeding plants with contrasting expressions for the same character (seed shape used in the example.)

Mendel’s Experimental Design

2. The parents were referred to as the first parental (P1) generation. The offspring produced from the cross is referred to as the first filial (F1) generation.

Law of Dominance – some traits are transmitted to and manifested in offspring more often than others

Dominant traits – traits that are expressedRecessive traits – traits that are hidden or

not expressed

Mendel’s Experimental Design

3. Mendel allowed the F1 plants to self-pollinate. He noted that some of the offspring expressed the recessive trait.

Two important observations:

When the F1 plants that expressed only the domonant trait were self-pollinated, some of their offspring (f2) expressed the recessive trait.

The ratio of the plants with dominant traits to the plants with recessive traits is almost 3:1

F1 plants have “unit determiners/characters”

F1 plants with yellow seed color – two unit determiners: one for the yellow, one for the green seed color

Mendel unit determiners Walter Sutton (1902) GENES

Mendelian Principles of Inheritance

Seed color G – yellow g – green:: G and g alleles (alternative/different

forms of the gene for the seed color):: genes appear in pairs :: yellow-seeded plants – GG:: green –seeded plants - gg

Phenotype – physical expression of the character

Genotype – set of genes that an organism has

Homozygous – gene pairs that are made up of identical genes

Heterozygous – gene pairs that are made up of dissimilar genes

Seatwork: Identify if the following gene pairs are homozygous or heterozygous

1. AA 6. SSrr2. Rr 7. GG3. aaBB 8. LLll4. MmNN 9. CCrr5. PpQq 10. Jj