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Plant gene)cs: This is an example from your text book, showing how sexual reproduc)on leads to combining genes and therefore “traits” in new combina)ons that can be beneficial or detrimental to progeny. The parental plants have differences in genotype. Genotype – the set of alleles (forms of a gene) present in an individuals genome. Where do differences in genotype arise? Generally by muta)on. A muta)on is a change in DNA sequence. Types of muta)on: Point muta)on: single base pair change that is either silent or leads to a change in the encoded protein or to a change in expression. Dele)ons and inser)ons Duplica)ons whole genes or even genomes can be duplicated. Effects of muta)ons: Muta)on in a promoter can change gene expression, the level, cell specificity, responsiveness to hormones, light, or stress, etc. Muta)on in an exon can be silent, or it can change change protein func)on, it can “knock out” protein func)on. Soma)c muta)ons do not lead to heritable changes because they occur in cells that are not in the germ line. Are all muta)ons heritable? No. Monohybrid cross, a cross of two heterozygous individuals Rr x Rr How to construct a PunneS square: 1. Figure out the genotype of gametes (sperm and egg) that can be made by each parent. 2. Put those on the outside of the square. 3. add the gametes together (fer)liza)on) to produce the genotype of the progeny. The genotypic ra)o of a monohybrid cross is 1:2:1 1 RR, 2 Rr, 1 rr One homozygous dominant, two heterozygous, one homozygous recessive. The PunneS square Phenotype – the observable characteris)cs of an organism Allele – form of a gene (R or r) dominant allele – phenotype of this allele is displayed in the heterozygous individual (phenotype of Rr is same as RR) recessive allele -­‐ only displayed in the homozygous recessive individual (rr) homozygous – both alleles in an individual are the same (RR or rr) heterozygous – two different alleles are different (Rr). If you cross a homozygous tall plant to a homozygous short plant and the progeny are short then which trait is recessive? How can you determine the genotype of any tall plant? Use a test cross: cross it to the homozygous recessive individual. This is a test cross: The phenotype of TT and Tt is the same (both tall). But you can determine the genotype of a tall plant by crossing it with S. If the tall plant is TT then all progeny will be Tt (tall). If the tall plant is Tt then 50% will be tall (Tt) and 50% will be short (S). Therefore you use the test cross to determine the genotype of the tall plant. What is the purpose of a test cross? Dihybrid cross, green pods are dominant to yellow pods, yellow seeds are dominant to green seeds. Parental Genotypes Parental gametes GGYY ggyy gy GY F1 genotype GgYy F1 gametes GY Gy gY gy Fill in the genotypes of progeny from a dihybrid cross of GgYy x GgYy Fill in the genotypes of progeny from a dihybrid cross of GgYy x GgYy GY
GY
Gy
gY
gy
Gy
gY
gy
Fill in the genotypes of progeny from a dihybrid cross of GgYy x GgYy GY
GY
Gy
gY
gy
GGYY
Gy
gY
gy
Fill in the genotypes of progeny from a dihybrid cross of GgYy x GgYy GY
GY
Gy
gY
gy
Gy
gY
gy
GGYY
GGYy
GgYY
GgYy
Fill in the genotypes of progeny from a dihybrid cross of GgYy x GgYy GY
Gy
gY
gy
GY
GGYY
GGYy
GgYY
GgYy
Gy
GGYy
GGyy
GgYy
Ggyy
gY
GgYy
GgYy
ggYY
ggYy
gy
GgYy
Ggyy
ggYy
ggyy
How many different genotypes resulted from this cross? (1:1:2:2:4:2:2:1:1) How may different phenotypes? What is the phenotypic ra)o? Next )me: fungi and lichens, read Ch. 24