GENETICS Dominant and Recessive Traits The study of genes, heredity, and variation in living organisms

REVIEW: GENE VS. ALLELE

GREGOR JOHANN MENDEL ● “Father” of genetics ● Famous because of his work with pea plants ● Tested over 5,000 plants! ● Mendel’s experiments with pea plants confirmed rules of heredity. o Today, the rules are known as Laws of Mendelian Inheritance (3) ● Mendel’s work was not recognized as significant until the end of the 20th century

MENDEL AND HIS PEAS: EXPERIMENT ● Terminology of chromosomes and genes, non-existence for Mendel. ● Mendel described the basic patterns of inheritance before the mechanism for inheritance was even discovered. ● Controlled reproduction of plants and studied traits expressed in offspring.

MENDEL AND HIS PEAS: EXPERIMENT DETAILS ● Cross pollinated plants to produce “pure breed” plants, which means Mendel “interbred” ● Mendel has to keep cross pollinating until all offspring were homozygous for the trait. o 2 alleles for a trait are the same o Sperm and egg each received the allele for pink flower color ● Did this with both alleles of a gene for flower color o produced homozygous plants with pink flowers o produced homozygous plants with white flowers

MENDEL AND HIS PEAS: EXPERIMENTAL RESULTS FOR “F1” GENERATION Flowers genotype: ? Mendel did not know Flower phenotype: pink and white crossed and all pink flowers produced. How? ● Homozygous pink flower X Homozygous white flower = all plants showed the color for pink flowers.

MENDEL AND HIS PEAS: EXPERIMENTAL RESULTS FOR “F1” GENERATION ● All flowers pink, why no white flowers? o Some alleles are dominant (you can physically see)Aa or AA o Some alleles are recessive (you cannot physically see), aa  F1 generation: heterozygous Pp

MENDEL AND HIS PEAS: EXPERIMENT “F1” INDIVIDUAL CROSSED WITH ANOTHER “F1” INDIVIDUAL ● F2 generation produced the following: o 75% dominant trait expressed (¾) o 25% recessive trait expressed (¼) ● White flower showed up because homozygous recessive. o “pp”

PHENOTYPIC RATIO 3:1 ● Mendel’s F1 experiment with peas shows simple inheritance patterns o Dominant alleles X recessive alleles o Homozygous dominant X homozygous recessive  All offspring 100% show dominant trait and all offspring are heterozygous for trait o Cross heterozygous dominant with heterozygous dominant then: 75% show the dominant trait 25% show the recessive trait 25% are Homozygous Dominant 50% are Heterozygous 25% are Homozygous recessive

1. LAW OF SEGREGATION Key concept: Law of segregation states that two alleles (one from each parent) coding for the same trait separate during meiosis This separation, or assortment, of homologous chromosomes is random.

2. LAW OF INDEPENDENT ASSORTMENT ● Key concept: inheritance of one trait has no effect on the inheritance of another ● Example: Cat fur color compared to cat tail length

GENOTYPE VS. PHENOTYPE

● An individual that is homozygous-dominant for a particular trait carries two copies of the allele that codes for the dominant trait. BB ● An individual that is homozygous-recessive for a particular trait carries two copies of the allele that codes for the recessive trait. bb DEFINITIONS:

 A tool that helps to show all possible allelic combinations of gametes in a cross of parents with known genotypes in order to predict the probability of their offspring possessing certain sets of alleles. PUNNETT SQUARES!

EXAMPLE: 2 FRUIT FLIES HETEROZYGOUS FOR EYE COLOR. (FF) CAPITAL F BEING DOMINANT RED COLOR Probable Genotype Results of Offspring: ● FF, 1:4 or 25% ● Ff, 2:2 or 50% ● ff, 1:4 or 25% Probable Phenotype Results of offspring: ● Wild-type (Red) 75% or 3:4 and white 25% or 1:4

SPONGE BOB MONOHYBRID PUNNETT SQUARES

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