Topic 4.3 Theoretical Genetics

4.3.1 Define the terms below: Genotype- refers to the alleles of an organism – ex. TT or tt – Usually written with lower case and upper case letters Phenotype- refers to physical characteristics of an organism – Ex. tall or short – Usually written as a word Dominant Allele- one that has the same effect on the phenotype whether present in homozygous or heterozygous state. ex. TT or Tt are both tall Recessive allele- only effects the phenotype if it is present in the homozygous state. ex. tt is short

Codominant alleles- pairs of alleles that both affect the phenotype when present in the heterozygous state ex. I A I B = type AB blood Locus- position of a gene on a chromosome Homozygous- having two of the same alleles ex. TT or tt Heterozygous- having two different alleles for a trait ex. Tt Carrier- is a heterozygous individual that has a copy of a recessive allele that causes a genetic disease, but does not have the disease Test Cross- testing an individual with a dominant phenotype to determine if they are heterozygous or homozygous. This is done by crossing the unknown individual with a homozygous recessive individual.

4.3.2 Monohybrid Cross Using a Punnett Grid punnett grid = a way of finding the expected ratio of the offspring of two parents the grid should be labelled to show the parents genotypes, gametes and offspring genotypes and phenotypes ex. parent genotypes ♂ = Tt and ♀ =Tt possible gametes ♂ = T or t ♀ = T or t TT tall Tt tall Tt tall tt short T t t

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4.3.2 (cont.) Practice a Simple Monohybrid Cross Tall is dominant and short is recessive in pea plants. Cross a heterozygous tall ♂ and a short ♀ pea plant. Give the genotypic and phenotypic ratio for the offspring. ♂ genotype = possible gametes = ♀ genotype = possible gametes = ♂ ♀ genotypic ratio = __________ phenotypic ratio =__________ Offspring

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How Did Mendel Cross His Pea Plants? He started with two pure breeding plants of alternate phenotypes ex. tall (TT) and short (tt). This was called the P generation (P for parent). Then he crossed the offspring of the P (Tt X Tt). This was called the F1 generation (first filial). The resulting offspring were called the F2 generation (second filial) He discovered many interesting patterns emerged from these types of crosses: F2 genotypic ratio was always 1:2:1 and phenotypic was always 3:1 Recessive phenotype skipped a generation

Practicing Monohybrid Crosses 1.Cross a homozygous green pod with a yellow pod plant. Green pods are dominant. G=green allele and g=yellow allele 2.Cross two heterozygous purple flowered pea plants. 3.Saguaro cacti are very tall cylindrical plants that usually have two L-shaped arms, one on each side. Suppose you lived in southern Arizona where the Saguaro cactus is common and you happen to have one growing in your yard. Your Saguaro has two arms but one is longer than the other. Now, assume that arm length in these cacti are controlled by a single gene with arms of the same length (A) being dominant to arms of different lengths. What is the genotype of your cactus?genedominantgenotype 4.Could one of the parents of your cactus have had a phenotype with arms the same length? If so, what would have been the genotype of that parent?phenotypegenotype 5.Suppose you cross your cactus with that of your neighbor which has arms of the same length. Your great grandchildren (it takes a Saguaro cactus a long time to mature) find that half of the resulting offspring have arms the same length and half have arms of different lengths. What was the genotype of your neighbor's cactus? genotype

4.3.3 Some Genes Have More Than 2 Alleles This is called Multiple Alleles With 2 alleles (ex. T and t) 3 genotypes are possible (TT, Tt and tt) and 2 phenotypes are possible (tall or short) Sometimes there are 3 or more alleles for a gene. Example = ABO blood groups in humans – I A is the allele for type A blood – I B is the allele for type B blood – i is the allele for type O blood There are 4 possible phenotypes (A, B, AB and O) And 6 different genotypes (I A I A, I A i, I A I B, I B I B, I B i and ii)

Remember I A and I B are codominant alleles: – I A I A and I A i give a phenotype of type A blood – I B I B and I B i give a phenotype of type B blood – I A I B give a phenotype of type AB blood – ii gives a phenotype of type O blood I A I B clearly shows codominance because neither allele is masked; both alleles are expressed in the phenotype of type AB blood _detailpage&v=KXTF7WehgM8

4.3.4 ABO Blood Groups are Examples of Codominance and Multiple Alleles Practice Problems: 1.A baby has blood type B, his mother has blood type A, his paternal grandfather has blood type A, and his paternal grandmother has blood type B. Determine a)the genotype of the baby b)All possible genotypes for the baby’s father 2.A man of blood type AB and a woman of blood type B are expecting a baby. The woman’s mother has blood type O. a)Deduce the possible phenotypes of the offspring from the cross. Include the parents’ genotypes, the gametes, the F1 genotypes and phenotypes.

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Punnett Squares DTl8 DTl8

Sex-Linkage Biozone pages

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Predict phenotypic and genotypic ratios of all types of monohybrid crosses: – Either/or- mendelian crosses – Codominance – Sex-linked – Multiple alleles

Deduce the genotypes and phenotypes of individuals in pedigree charts Biozone pages

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Non-Mendelian Genetics Yhs Yhs

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Probability _Jc _Jc

Statistics for Science RI RI

Graphing Data 6Mo 6Mo

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