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Objective 1. Use the punnett square method to determine the possible genotypes of different monohybrid crosses 2. Determine the phenotypic ratio of a monohybred.

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Presentation on theme: "Objective 1. Use the punnett square method to determine the possible genotypes of different monohybrid crosses 2. Determine the phenotypic ratio of a monohybred."— Presentation transcript:

1 Objective 1. Use the punnett square method to determine the possible genotypes of different monohybrid crosses 2. Determine the phenotypic ratio of a monohybred cross. 3. Explain how the process of meiosis and fertilization account for the transmission of inherited characteristics.

2  The transfer of characteristics (traits) from one generation to another  Your inherited characteristics (traits) are determined by the genes located on your chromosomes

3 Dominant Trait Description # of students with Dominant # of students with Recessive Ratio of Dominant to Recessive Percentage with Recessive traits Class Eye colour Hair colour Hairline Freckles Earlobe Fingers Ear rim Thumb joint Folded hands Tongue rolling Chin dimple

4  a short segment of a chromosome coding for one trait

5  chromosomes are found in pairs  in humans, there are 46 chromosomes, made up of 23 pairs of homologous chromosomes  a pair of chromosomes consists of two homologous chromosomes which look alike and carry genes for the same traits  you receive one homologous chromosome of the pair from each parent, therefore you receive 2 genes for each trait

6  This term is used to describe the physical or visible appearance of an individual as determined by the gene combination you inherit from your parents.  Example: in the case of eye colour, having brown eyes is the phenotype and is dominant

7  the gene combination that produces the trait  these genes may be the same or different  genotypes are represented by upper and/or lower case letters e.g. Bb  there are three possibilities for genotypes for a single trait.  e.g. BB or Bb or bb

8  alternate forms of a gene  same location on a each chromosome of pair  affects the same trait but differently  alleles are different forms of a gene that carry different instructions  eg. Brown eyes or blue eyes

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10  Characteristic that is always expressed its gene is present  only one dominant allele needs to be present for the dominant trait to be expressed  an upper case letter designates a dominant allele  eg. Tall is dominant. It is represented with a “T”

11  Characteristic that is only expressed when two genes for that trait are present  two recessive alleles need to be present for a recessive trait to be expressed  if a dominant allele is present it “masks” the recessive allele  eg: Short is recessive. It is represented with a  “t”

12  “homo” means the “same”  the condition where both alleles for a trait are the same  there are two conditions for homozygous genotype:  homozygous recessive genotype “aa”  homozygous dominant genotype “AA”

13  “hetero” means “different”  the condition where both alleles for a trait are different  the genetic information inherited for a trait from both parents is different  example: heterozygous genotype “Aa”

14  Summary (example eye colour) GenotypeConditionPhenotype BBHomozygous dominant Brown eyes BbHeterozygousBrown eyes bbHomozygous recessive Blue eyes

15  Crossed two purebred parents (One tall -T and one short -t)  Pure breeding plants always produce identical offspring.  All offspring were tall!! Mendel concluded that some traits were ___________ and some traits were ___________.

16  When individuals with different traits are crossed, the offspring (F1 generation) will express only the dominant trait. Parents:Tallx Short F1 (Offspring):TallTallTallTall What must the genotype of the offspring be if the parents were pure breeding?

17  Mendel crossed the F1 generation.  He crosses two hybrid pea plants.  Hybrids have contrasting traits.  F1: Tall plants xTall plants  F2 (Offspring of F1): Tall Tall TallShort  F2 generation = 3:1 ratio  What must the genotype of these offspring be if the parents were hybrids (Tt and Tt)?

18  Each F1 parent starts with two hereditary factors (alleles); one is dominant and one is recessive  Each parent contributes only one factor (allele)  Each offspring inherits one factor (allele) from each parent  If the dominant factor (allele) is present it will be expressed.  If the recessive factor (allele) is present it will only be expressed if only recessive factors are present.

19  Mendel crossed two purebred plants  TT – tall plant  Tt – short plant  Monohybrid cross – only one trait is being tested

20  Punnett Square  Is a grid system resembling a checkerboard, used in computing possible results of various genetic combinations  Simply stated, it is a way of representing the possible combinations of genes when an egg and sperm unite in fertilization

21 Characteristic hair texture – ◦ Dominant allele (gene) is curly hair - C. ◦ Recessive allele (gene) is straight hair - c  Mother ◦ Phenotype – straight hair ◦ Genotype- homozygous recessive - cc  Father ◦ Phenotype – curly hair ◦ Genotype – homozygous dominant – CC

22 Egg Sperm cc C Cc C All of their children will have curly hair. They all have a different genotype from their parents.

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27 Your Turn  Bikini Bottom Genetics – Monohybrid Crosses  HOMEWORK: Find out what the following words mean…  Hybrid  Pure-breeding/Purebred  Why was it important that Mendel used purebred plants in his experiment?  How does meiosis ensure that you inherit your mothers and fathers characteristics?

28 Objectives: 1. Explain what co dominance and incomplete dominance is. Give an example of each. 2. Use a Punnett square to solve basic incomplete and co dominance crosses 3. Use a Punnett square to solve basic dihybrid crosses.

29  Incomplete Dominance: When two alleles are equally dominant, they interact to produce a new phenotype.  Codominance: When both alleles are dominant and are expressed at the same time.  Pg 145 # 1-4

30  When a red bull is crossed with a white cow, the offspring will be roan.

31 When a red flower is crossed with a red flower, the resulting offspring will be pink.

32  A type of cross that involves two genes, each consisting of non identical alleles.

33 RY ry In his second experiment Mendel crossed a pea plant with round/yellow (RRYY) seeds with a pea plant with wrinkled/greed seed (rryy). What genotypes resulted? What phenotypes resulted? RY ryRrYy ryRrYy Genotype: RrYyF1 - Generation Ratio 100% Phenotype: Round/Yellow Ratio100%

34 RYRyrYry RY Ry rY ry RYRyrYry RYRRYYRRYyRrYYRrYy RyRRYyRRyyRrYyRryy rYRrYYRrYyrrYYrrYy ryRrYyRryyrrYyrryy What genotypes resulted? What phenotypes resulted? Genotype: RRYY RRYy RryyRrYYRrYyrrYYrrYyrryy Ratio: Phenotype: Round/Yellow Round/Green Wrinkled/Yellow Wrinkled/Green Ratio:9331 In the resulting F2 – Generation, the phenotypic ratio will always be 9:3:3:1 In other words, the likelihood of obtaining each of the above phenotypes from crossing two hybrid pea plants is 9:3:3:1.

35  The inheritance of alleles for one trait ________ (does/does not) affect the inheritance of alleles for another trait.

36  Bikini Bottom  Questions


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