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
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