Published on March 4, 2014
Introduct ion to Genetics
Genetics The scientific study of heredity
Gregor Mendel Father of Genetics! Austrian Monk - worked at monastery and taught high school Grew peas and became interested in the traits that were expressed in different generations of peas
True breeding Each and every offspring (produced through self fertilization) have exactly the same traits as the parents – also known as purebred He was also able to cross breed peas for different traits
Self Fertilization Plants have both male and female parts so they are able to fertilize themselves Cross Pollination When male parts from one plant are dusted with pollen from another plant thus crossing the pollen!
Genes and Dominance Mendel studied seven different pea plant traits Each trait he studied had a contrasting form
Pea Plant Traits
Genes and Dominance The offspring of crosses between parents with different traits are called Hybrids When Mendel crossed plants with different traits he expected them to blend, but that’s not what happened at all. All of the offspring had the character of only one of the parents
Mendel drew two conclusions 1. Inheritance is determined by genes that are passed from generation to generation
Mendel’s 2 conclusion nd 2. The Principal of Dominance Some alleles are dominant and some are recessive
Alleles Different forms of a gene Either dominant or recessive
dominant Covers up the recessive form – gene that if present, is always expressed (Capital letter!) Ex.) T = tall
recessive Gene that gets covered up if there is a dominant allele present (lower case letter) Ex.) t = short
Mendel wanted to know Q: Had the recessive alleles disappeared? To find out, Mendel mated the F1 plants to produce an F2 generation! (grand kids! )
P1 Parental Tall Short F1 All Tall F2 3 tall : 1 short 75% tall 25% short
The F1 Cross The recessive traits reappeared! Roughly 1/4 of the F2 plants showed a recessive trait (tt)
Segregation Ratio 3:1 At some point, the allele for shortness had been separated from the allele for tallness. This occurred during the formation of SEX CELLS (when moms egg and dad’s sperm are produced)
Punnett Square Vocab If you do not know the following vocabulary words you will fail miserably
Punnett Square Diagram used to determine genetic crosses
Probability The likelihood that a particular event will occur Random
Homozygous Organisms that have 2 identicle alleles for a trait Ex.) TT , tt
Heterozygous Have two different alleles for a trait Ex.) Tt
Phenotype Physical characteristics – The thing you see WORDS Ex.) Tall
Genotype Genetic make-up LETTERS Ex.) Tt, TT, tt
Mendel wondered if alleles segregate during the formation of gametes independently Does the segregation of one pair of alleles affect the segregation of another pair of alleles? For example, does the gene that determines whether round or wrinkled in shape have anything to do with the gene for color? Must a round seed also be yellow?
All heterozygous 9:3:3:1 Ratio
Independent Assortment Genes that segregate independently do not influence each others inheritance
Incomplete Dominance When one allele is not dominant over another Four o’clock flowers The heterozygous phenotype is somewhat blended between the two homozygous phenotypes
Codominance When both alleles contribute to the phenotype of an organism Ex.) Speckled Chickens
Multiple Alleles When more than two possible alleles exist in a population Ex.) blood type IA Dominant IB i Recessive
Human Blood Types Phenotype A Genotype IAIA or IAi B IBIB or IBi AB IA I B O ii
Polygenic Traits Traits controlled by two or more genes Ex.) eye color, skin color
Genetics and the Environment Some characteristics are determined by interactions between genes and the environment Ex.) genes may affect a plants height but the same characteristic is influenced by climate, soil conditions and availability of water
Do Now Human hair is inherited by incomplete dominance. Human hair may be curly (CC) or straight (cc). The heterozygous genotype (Cc) produces wavy hair. Show a cross between two parents with wavy hair
Mendel’s principles of genetics require at least 2 things 1. Each organism must inherit a single copy of every gene from each of its parents 2. When an organism produces its own gametes these two sets of genes must be separated from each other so that each gamete contains just one set of genes
Homologous Chromosomes that each have a corresponding chromosome from the opposite sex parent
Genetics and Heredity- Powerpoint - I Love Science
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