Genetics Genetics

Glossary Phenotype The observable physical or behavioral traits of an organism, determined by the organism's genotype. Genotype The alleles present in a particular individual that give rise to the individual's phenotype. Homozygous A genotype where both alleles are the same, Either homozygous dominant AA or homozygous recessive aa. F1 The F1 (first filial) generation is the hybrid offspring produced in the cross pollination of P (parental) generation true breeding plants. True-breeding For a particular characteristic being studied, plants that, when self-pollinated, produce offspring with the same trait. These will have homozygous genotypes. Hybrid An individual that results from a cross between two different strains. These individuals will be heterozygous. Gene A set of segments of nucleic acid that contains the information necessary determine a particular characteristic. Allele One of multiple alternative forms of a single gene.

Chromosomes Chromosomes are found in pairs (except gametes) The two chromosomes in a pair come from different parents Each chromosome carries different genes

Haploid and diploid Gametes are _________ as the type of cell division halves the number of chromosomes. Body cells (somatic cells) are __________. In humans, the haploid number is ________. The diploid number is _______. ___________ are produced by a type of cell division called _________ which halves the chromosome number. During _______ the chromosomes from two gametes are combined to restore the diploid number.

In humans….

Genotypes recessive homozygous dominant heterozygous Newfoundland dogs have either black or Landseer (black and white) fur. The colour is determined by one gene of which there are two alleles, B resulting in black fur and b resulting in Landseer when homozygous. B B B b b b OR recessive Homozygous dominant Heterozygous Homozygous recessive Draw the genotypes above Use the words to label the genotypes heterozygous homozygous dominant

Genes and chromosomes The position of a gene on a chromosome is the locus The DNA in the chromosome has replicated to produce two chromatids This is how the chromosomes appear during prophase of mitosis and Prophase 1 of Meiosis

Which letters? Aa Bb Cc Dd Ee Ff Gg Hh Ii Jj Kk Ll Mm Nn Oo Pp Qq Rr Ss Tt Uu Vv Ww Xx Yy Zz

Offspring may have different features to their parents We can sometimes deduce the animal’s genotypes What are the genotypes of Zelda and Zach? Different crosses give different F1 phenotypic ratios

Gregor Mendel 1822 - 1884 Gregor Mendel studied the INHERITENCE of certain CHARACTERISTICS in pea plants. He called his pea plants his “children”!

Genetic Diagrams Give the phenotypes Show the genotypes Write out the gametes Draw a Punnet square State the ratios Short Tall TT tt T T t t t T Tt Tall Dwarf pollen ova 3 Tall: 1 Dwarf

Genetic Diagrams Tall Give the phenotypes Show the genotypes Write out the gametes Draw a Punnet square State the ratios Tall Tt Tt T t T t T t TT Tall Tt tt Dwarf pollen ova 3 Tall: 1 Dwarf

Genetic Problem Gregor Mendel crossed true-breeding pea plants with purple flowers with a pea plant with white flowers. The resulting seeds were planted and later self pollinated. The F1 plants produced seeds( F2) that grew into 705 plants with purple flowers and 214 plants with white flowers. What is the ratio of purple to white flowers in the F2 generation?? Which characteristic is dominant? Suggest a letter to represent the alleles . Produce genetic diagrams to explain the outcomes in both the F1 and F2 generations.

Genetic Diagrams – Monohibred Inheritance Bb BB Purple flowers bb White Flowers Give the phenotypes (F1) Show the genotypes Write out the gametes Draw a Punnet square State the ratios (F2) All Purple flowered plants

Genetic Diagrams – Monohibred Inheritance Give the phenotypes (F1) Show the genotypes Write out the gametes Draw a Punnet square State the ratios (F2) Purple flowers Purple Flowers Bb Bb Bb Bb B b b B B b b 3 Purple: 1 White

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Test Crosses Dalmatians can have black spots of liver (brown spots) Choose a letter for the colour of the spots. What are the possible genotypes of the black spotted dogs. An owner has a black spotted bitch of unknown genotype. She is crossed with a liver spotted dog. What are the likely outcomes if the bitch is i) homozygous ii) heterozygous? Produce genetic diagrams to explain your answers. Why do test crosses always involve crossing with a homozygous recessive individual?

Guinea pigs In guinea pigs, black fur is dominant to white fur. A test cross is done to find the genotype of a black furred male guinea pig (test cross). What will be the phenotype of the female guinea pig. What does a litter of seven black furred and one white furred tell you about the genotype of the male guinea pigs? What will be the genotypes of the black furred baby guinea pigs?

Tomatoes In tomato plants, indented ‘wild type’ is dominant to non- indented ‘potato type’. Copy and complete the table below: Male parent (Pollen) Female parent (Ova) Expected phenotypic ratios of the F1 generation Homozygous dominant Homozygous recessive 1 wild type : 1 potato type Heterozygous wild type Homozygous potato type All potato type

Drosophila In Drosophila, straight wings are dominant over curled. Straight winged flies are crossed with curled winged flies. All the offspring (F1) had straight wings. Suggest suitable letters for the alleles determining the shape of wings in Drosophila. Which allele is dominant. Produce a genetic diagram to show the outcome of using the F1 flies to produce an F2 generation.

Cystic Fibrosis (CF) Cystic fibrosis (also known as CF) is an autosomal recessive genetic disorder that affects the lungs, and also the pancreas, liver, and intestine. It leads to thick, viscous secretions. Lung infections are more frequent and of greater severity leading to permanent tissue damage. One in 23 people of Western European origins is a carrier for CF resulting in around one in every 2000 births.

Cystic Fibrosis (CF)

Cystic Fibrosis (CF) Draw a genetic diagram showing the typical inheritance of the condition within a family. How do the lungs usually “clean” themselves and prevent infection? Why is this a problem in CF sufferers? Why are CF sufferers often under weight? There have been hopes that gene therapy may offer effective treatment for CF. What is gene therapy and why is CF a focus for the development of gene therapy?

Cystic Fibrosis Normal Normal Gg Gg G g G g G g GG Gg gg Sperm ova Let G be the normal allele and g be the allele for Cystic Fibrosis Phenotypes Genotypes Gametes Punnet square Ratio: 3 normal: 1 Cysctic Fibrosis Normal Normal Gg Gg G g G g G g GG Gg gg Sperm ova

Cystic Fibrosis Let A be the allele for healthy and a for cystic fibrosis The diagram on the right shows a pedigree chart for a family where there are individuals with cystic fibrosis. Suggest the genotypes of III3 II1 II2 I4 I1 is homozygous. Draw a genetic diagram to show the passing on of the cystic fibrosis allele from generation I to II1. Produce a genetic diagram to show the passing on of alleles from generation II to III.

Huntington’s Chorea (or disease) State whether Huntington’s chorea is caused by a dominant or recessive gene. Compare the inheritance of Huntington’s to the pattern of inheritance for cystic fibrosis

Japanese Waltzing Mice PHENOTYPE Normal X waltzing (Characteristic) GENOTYPE NN X nn (The alleles) Gametes N or N n or n PUNNET SQUARE Normal behaviour is dominant = N Waltzing behaviour is recessive = n Crossing homozygous normal mice with homozygous mice results in a F1 entirely consisting of heterozygous normal mice n N Nn

Japanese Waltzing Mice PHENOTYPE Normal ___ X waltzing (Characteristic) GENOTYPE Nn X nn (The alleles) Gametes N or n n or n PUNNET SQUARE Normal behaviour is dominant = N Waltzing behaviour is recessive = n Crossing an F1 (Nn) mouse with a waltzer results in a ratio of 1 normal : 1 waltzer in the next generation. n N Nn nn

H h Hh H h Hh hh HERBERT Lincoln Red SON OF HERBERT Herbert’s offspring would have a white face, Larry’s would not. Amongst Herbert’s “grandcalves”, half would have white heads, half would not. Let H be the Herreford allele for white head and h for the Lincoln Red allele of entirely red. Lincoln Red