Mendelian Genetics Gregor Johann Mendel 1822 1884 father

Mendelian Genetics Gregor Johann Mendel (1822 -1884) “father of genetics”

Many people believed that parents’ traits were “blended” in their offspring. . . A short mother Would produce a child of average height A tall father

Mendel, an Austrian monk, disproved this theory of “blended” traits by studying traits in pea plants.

Mendel chose the pea plant for 3 reasons. . . 1. Structure of the flowers (to control fertilization) 2. Presence of 7 distinct traits (see Figure 6. 5, p. 133) 3. Rapid reproduction cycle of about 90 days

Mendel studied more than 20, 000 pea plants for more than 8 years.

Mendel observed 3 generations of pea plants: P = Parental F 1 = First Filial F 2 = Second Filial

Instead, only the dominant trait appeared in the F 1 generation, while the recessive trait remained hidden In the F 2 generation, the recessive trait reappeared. Mendel proved that traits do not “blend. ”

Mendel concluded that a pea plant must carry a pair of “factors” for every trait.

We now know these “factors” as genes. Genes = sections of a chromosome that code for a trait

Allele = a distinct form of a gene ex: one allele might code for red hair, another for brown hair.

Heredity X Each offspring has two alleles for each gene, one from each parent.

Dominant allele = form expressed when 2 different alleles are present. ex: the F 1 generation to the left has alleles for green and yellow, but only yellow is expressed. Yellow (Y) is dominant in this case.

Recessive allele = expressed when paired with a dominant gene. ex: the green (y) allele is present in the F 1 generation but it is recessive because it is not expressed.

Remember, in SEXUAL reproduction… …to form a …which grows into a HAPLOID gametes DIPLOID join…fetus zygote

Sexual Reproduction Haploid sperm (gamete) 1 n Haploid egg (gamete) + 1 n Diploid zygote = 2 n

s t i r e h n i e t o g y z e h t , e r o f s e t r n e e r Th a p m o r f s t i a tr Heredity is the passing of traits or characteristics from parents to offspring

Genotype = actual genetic makeup of an organism (genes) Phenotype = outward expression of trait (photo)

Genotype Purebred for dominant yellow YY Phenotype YY = yellow

Genotype Hybrid for dominant yellow and recessive green Yy Phenotype Yy = yellow

Genotype Purebred for recessive green yy Phenotype yy = green

Homozygous = the two alleles in a pair are identical; ex: YY and yy Purebred puppies are homozygous for quite a few traits.

Heterozygous = the two alleles in a pair are different; ex: Yy A hybrid mutt is heterozygous for quite a few traits.

Mendel’s Laws 1. Law of Segregation 2. Law of Independent Assortment 3. Law of Dominance

Mendel’s Laws 1. Law of Segregation: each pair of genes segregate during meiosis 2. (organisms can only give half of their genes to their

Mendel’s Laws 2. Law of Independent Assortment: gene pairs segregate into gametes randomly and independently of each other. 3. (most traits are not linked, do not have to be passed together)

Law of Independent Assortment X

Law of Independent Assortment We now know that some genes are linked, therefore always passed together

Mendel’s Laws 3. Law of Dominance: the dominant allele is expressed and the recessive allele can be hidden

Try your hand at breeding pea plants… Click on the website below: http: //www. sonic. net/~nbs/projects/anthro 201/exper/

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In 1903, Walter Sutton developed the Chromosome Theory of Heredity. . .

Chromosome Theory of Heredity 1. Chromosomes occur in pairs 2. Chromosomes separate during meiosis 3. Chromosome pairs sort independently