taboo rap gen lec
Prepared By:Montalbo, Daniel Justin B.De Castro, Ralph Louis R.
Mendel’s Law of Segregation states that there are two alleles for every gene determining a specific characteristic, and these alleles are segregated into separate gametes during reproduction.
When the 2 different alleles occur together in one individual (heterozygote), the dominant allele will be the one that is expressed in the phenotype of the individual.
The Law of Addition is used to combine probabilities, when there are 2 or more ways to arrive at a given outcome.
The Law of Multiplication is used to combine probabilities of 2 or more different events that need to occur in combination.
Mendel’s Law of Independent Assortment says that 2 or more different genes, if found on separate chromosomes, are determined independently of each other.
Many characteristics have been found to follow patterns of inheritance that are modifications of Mendel’s rules.
• genegene• alleleallele• dominantdominant• recessiverecessive• charactercharacter• traittrait• phenotypphenotyp
• pure pure breedingbreeding
• hybridhybrid• homozygouhomozygou
usus• P (parental P (parental
• FF11 (first (first filial filial generation)generation)
• FF22 (second (second filial filial generation)generation)
• Punnett Punnett SquareSquare
• forked forked lineline
• polygenespolygenes• contributcontribut
ory alleleory allele• non-non-
contributcontributory alleleory allele
• continuoucontinuous s variationvariation
• discontindiscontinuous uous variationvariation
• Pre-Mendel beliefs in genetics: blending theory
• Augustinian monk and science teacher
• Why Pisum sativum?– Pea plants available in
many varieties• character (heritable feature)
• trait (character variant)
– Perfect flowers• cross-pollination and
– Short generation time– Many offspring
P Generation(true-breeding parents)
F1 Generation (hybrids)
All plants hadpurple flowers
705 plants 224 plants
MONOHYBRID CROSS inheritance of a single trait
Allele for purple flowers
Locus for flower-color gene
Allele for white flowers
Alternative versions of genes exist (alleles)› Dominant› Recessive
Organism inherites 2 alleles› Dominant is fully
expressed› Recessive has no
visible effect Law of
segregation› 2 alleles for one
character separate and go to different gametes
xTrue-breeding plants have identicalalleles.
Gametes each contain only one allele for the flower-color gene. Every gamete produced by one parent has the same allele.
F1 hybrids have a Pp combination. Purple-flower allele is dominant, all hybrids have purple flowers.
Hybrid plants produce gametes, two alleles segregate: half the gametes receiving the P allele and the other half the p allele.
3 : 1
Punnett square: shows all possible combinations of alleles in offspring from an F1 x F1 (Pp x Pp) cross.
Each square represents an equally probable product of fertilization.
Random combination of the gametesresults in the 3:1 ratio that Mendelobserved in the F2 generation.
• Homozygous – identical alleles, true-breeding
• Heterozygous – different alleles
• Phenotype – physical appearance
• Genotype – genetic make-up
Dominant phenotype,unknown genotype:
PP or Pp?
Recessive phenotype,known genotype:
If PP,then all offspring
If Pp,then 1⁄2 offspring purpleand 1⁄2 offspring white:
An organism displaying the dominant phenotype can eitherbe homozygous or heterozygous for the trait. A test-cross willhelp determine which.
The individual with the unknown genotype is crossed with a homozygous individual expressing the recessive trait (white flowers in this example). By observing the phenotypes of the offspring resulting from this cross, we can deduce the genotype of the purple-flowered parent.
Illustrates the inheritance of two characters
Produces four phenotypes in the F2 generation
Law of Addition - combines probabilities for mutually exclusive events
The Law of Multiplication - combines probabilities of 2 or more independent events that need to occur together
Forked Line Method
AaBbCc x AaBbCc
1. Codominance – two dominant alleles affect
phenotype in separate ways
– both alleles manifest– e.g. roan coloring in
horses – both red and white
2. Incomplete dominance – phenotype of offspring is
between phenotypes of two parents
– e.g. red and white parents give rise to pink offspring
3. Multiple alleles– genes with more than two
alleles that control the phenotype
– e.g. ABO blood type system has 3 alleles--A,B,i. A and B are codominant, i is recessive to both