2 Gregor Mendel 1822-1884 - The father of genetics Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experimentsTrue-breeding peas – self-pollinateWanted to stop self pollination he cut away the pollen-bearing male parts and dusted pollen from another plant onto the flower – cross-pollination
3 Mendel’s 7 TraitsTrait – specific characteristic, such as seed color or plant height – makes one different from the otherMendel crossed plants with each of the 7 traits and studied their offspring (hybrids)P (parental) – original pair of plantsF1 (first filial) – offspringFilius and filia are Latin for “son” and “daughter”
4 Mendel’s 7 Traits cont.He first concluded that biological inheritance is determined by factors that are passed from one generation to the next.Factors that determine traits are genesDifferent forms of a gene are called allelesHis second conclusion: the principle of dominance (some alleles are dominant & others are recessive)
5 Mendel’s 7 Traits cont.Did the recessive alleles disappear, or were they still present in the F1 plants?7 kinds of F1 to produce an F2 through self-pollinationRecessive alleles disappeared in F1 and reappeared in F2Alleles in F1 separated from each other during the formation of sex cells (aka gametes)
6 When similar crosses were repeated, similar results were obtained ie. Crossed 2 plants that were hybrid for stem height (Tt), about ¾ were tall and ¼ were shortProbability – likelihood that a particular event will occurThis can be used to predict the outcomes of genetic crosses
7 Punnett SquareChart that shows all the possible combinations of alleles that can result from a genetic crossused to show all the possible outcomes of a genetic cross and to determine the probability of a particular outcomeTtTTTtTTtttt
8 Coin Toss Lab Please take out your handout We will use the remainder of the period to work on and complete this lab
9 How are dimples inherited? Page 268 in Biology Text Book1. Write the last 4 digits of your telephone number. These 4 random digits represent the alleles of a gene that determines whether a person will have dimples.Odd = allele for the dominant trait of dimplesEven = allele for the recessive trait of no dimples2. First 2 digits represent a certain father’s genotype. Symbols D and d to write his genotype.
10 3. Use the last 2 digits the same way to find the mother’s genotype. 4. Construct a Punnett square for the cross of these parents. Then, using the Punnett square, determine the probability that their child will have dimples.5. Determine the class average of the percent of children with dimples.
11 Homozygous – organisms that have 2 identical alleles for a particular trait (ie. TT or tt) – true-breeding.Heterozygous – organisms that have 2 different alleles for the same trait (ie. Tt) – hybrid.
12 Phenotype – physical characteristics Things you can seeGenotype – genetic makeupThings you cannot see – ie. genes (made of DNA) on chromosomesMendel performed an experiment to see if seed shape affects seed color – crossed plants and recorded the two traitsOne did not effect the other (independent assortment) – genes for different traits can segregate independently during formation of gametes.
13 Summary of Mendel’s Principles Inheritance of biological characteristics is determined by genes.When two of more forms of the gene for a single trait exist, some forms may be dominant and others recessive.In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These are segregated from each other when gametes are formed.Alleles for different genes usually segregate independently of one another.
14 Dominant & Recessive Alleles Cases in which one allele is not completely dominant over another are called incomplete dominance (heterozygous phenotype is between the two homozygous phenotypes.Codominance – both alleles contribute to the phenotype. (ie. in chickens, the alleles for black feathers is codominant with the allele for white feathers.
15 Incomplete dominance - neither allele is dominant, red x white = pinkCodominance - both are expressed in some way,red x white = white/red spots
16 Many genes have more than two alleles, known as multiple alleles. Does not mean that an individual can have more than two allelesMeans that more than two possible alleles exist in a population – ie. rabbit coat colorTraits controlled by two or more genes are said to be polygenic traits – “having many genes.”Often show a wide range of phenotypesie. wide range of skin color in humans – more than 4 different genes control this trait
17 Chromosomal Inheritance Mendel’s principles of genetics requires;Each organism must inherit a single copy of every gene from each “parent”When an organism produces its own gametes, those 2 sets of genes must be separated so that each gamete contains just one set of genesie. Body cell in an adult fruit fly has 8 chromosomes (4 from male parent, and 4 from female parent) – these two sets of chromosomes are homologous
18 A cell that contains both sets of homologous chromosomes is said to be diploid – 2 sets Represented by the symbol 2Nie. For the fruit fly the diploid number is 8 or 2N=8Diploid cells contain two complete sets of chromosomes and two complete sets of genesSingle set of chromosomes – single set of genes are haploid – 1 set or N=4 for a fruit fly
19 Phases of MeiosisMeiosis – process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cellUsually involves 2 distinct divisions known as meiosis I and meiosis II
20 Meiosis I Before meiosis I, each chromosome is replicated. Cells start to divide – 4 chromosomes line up in the middle of the cell and 2 chromatids that make up each chromosome separateProphase – each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad4 chromatids in a tetradAs tetrads are formed, they exchange portions of their chromatids in a process called crossing-over
21 Meiosis I cont…Crossing-over, results in the exchange of alleles between homologous chromosomes and produces new combos of allelesHomologous chromosomes separate, and two new cells are formedSEE PAGE 276 FIG (MEIOSIS)
22 Meiosis II2 cells produced by meiosis I now enter a second meiotic divisionEach of the cell’s chromosomes has 2 chromatidsMetaphase II - chromosomes line up in the center of each cellAnaphase II – paired chromatids separate
23 See Page 278 FigMeiosis produces four genetically different haploid cellsIn males, meiosis results in four equal-sized gametes called spermIn females, only one large egg cell results from meiosis (the other 3 cells are polar bodies and are not involved in reproduction)
24 Mitosis vs. MeiosisMitosis results in the production of two genetically identical diploid cellsAllows an organism’s body to grow and replace cellsIn asexual reproduction, a new organism is produced by mitosis of the cell or cells of the parent organismMeiosis produces four genetically different haploid cellsBegins with a diploid cell but produces four haploid (N) cellsIs how sexually reproducing organisms produce gametes
25 Gene LinkageThomas Hunt Morgan researched fruit flies which led to the principle of linkageEach fruit fly has four pairs of chromosomes – each chromosome is a group of genesIt is the chromosomes that assort independently, not the genesIf two genes are found on the same chromosome they are not linked forever - crossing-over during meiosis sometimes separates genes