biology-class-12-unit-06-chapter-07-genetics-evolution-principles-of-inheritance-variation-l-7-7-2g2n8ssqnyw

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Multiple allelism </primary>
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- Occurrence of many alleles for a particular gene, controlling a particular character seen in different individuals of a population

- Each allele may produce a different phenotype

- Multiple alleles occur in the same locus of a homologous chromosome

- They are the mutant forms of the same gene

- They affect a same trait

- E.g. ABO blood group system

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<footer style = "font-size: 18px"> $\rightarrow$ Genetics and evolution Molecular basis of inheritance $\rightarrow$ <span style = "color:blue"> Multiple allelism </span> $\rightarrow$ ABO blood system $\rightarrow$ ABO blood system </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> ABO blood system </primary>
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- ABO Blood system was discovered by Landsteiner

- AB blood group was discovered de Castello and Steini in 1902

- Blood grouping is based on antigens present on the surface of RBC

- Antibody is present in the serum

- There are four types of blood groups, such as A, B, AB and O

- They are produced by different three different alleles. represented by |A |B |O

- I stands for immunoglobulin

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<footer style = "font-size: 18px">Genetics and evolution Molecular basis of inheritance $\rightarrow$ Multiple allelism $\rightarrow$ <span style = "color:blue"> ABO blood system </span> $\rightarrow$ ABO blood system $\rightarrow$ ABO blood system </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> ABO blood system </primary>
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- I<sup>A</sup> allele is dominant over I<sup>o</sup> allele

- I<sup>B</sup> allele is dominant over I<sup>o</sup> allele

- I<sup>A</sup> and I<sup>B</sup> alleles are co-dominant

- I<sup>o</sup> allele is recessive

- In ABO blood group system, there are 4 different phenotypes and 6 different genotypes

- A blood group is produced by I<sup>A</sup> allele

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<footer style = "font-size: 18px">Multiple allelism $\rightarrow$ ABO blood system $\rightarrow$ <span style = "color:blue"> ABO blood system </span> $\rightarrow$ ABO blood system $\rightarrow$ Multiple allelism </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Multiple allelism </primary>
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- Definition: more than two alleles

- (more than 2 alleles exist in a population not an individual)

- Example: rabbit's coat color

- Example: human's blood type

- **blood-type donors and recipients**

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<footer style = "font-size: 18px">ABO blood system $\rightarrow$ ABO blood system $\rightarrow$ <span style = "color:blue"> Multiple allelism </span> $\rightarrow$ Codominance $\rightarrow$ Coat colour in rabbit </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Chromosome theory of heredity </primary>
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- Put forward by Sutton and Boveri

- According to them the pairing and segregation of a pair of chromosomes would lead to the segregation of a pair of factors they carried

- Sutton united chromosomal segregation with Mendelian principles

- This theory states that chromosomes are the vehicles of inheritance as they carry the hereditary factors or genes and these hereditary factors are transferred parents to offsprings through successive generations

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<footer style = "font-size: 18px">Codominance $\rightarrow$ Coat colour in rabbit $\rightarrow$ <span style = "color:blue"> Chromosome theory of heredity </span> $\rightarrow$ Chromosome theory of heredity $\rightarrow$ Parallelism between the genes and chromosomes </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Chromosome theory of heredity </primary>
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- Chromosome theory of hereditary was later confirmed and experimentally proved by Morgan, Sturtevent and Bridges

- They established the fixed and definite position of genes in the chromosomes

- This theory forms the basis of modern genetics

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<footer style = "font-size: 18px">Coat colour in rabbit $\rightarrow$ Chromosome theory of heredity $\rightarrow$ <span style = "color:blue"> Chromosome theory of heredity </span> $\rightarrow$ Parallelism between the genes and chromosomes $\rightarrow$  </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Parallelism between the genes and chromosomes </primary>
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- Both genes and chromosomes are seen as pairs and each member of the pair is contributed by different parents

- Genes remain unaltered in the subsequent generations

- Both will segregate at the time of gamete formation and only one of each pair will move to one gamete

- Segregation of one pair is independent from the segregation of the other pairs

- Paired condition is regained by fertilisation

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<footer style = "font-size: 18px">Chromosome theory of heredity $\rightarrow$ Chromosome theory of heredity $\rightarrow$ <span style = "color:blue"> Parallelism between the genes and chromosomes </span> $\rightarrow$ _Drosophila melanogaster_ $\rightarrow$ Phenotypes of _Drosophila melanogastor_ </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> _Drosophila melanogaster_ </primary>
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- Why they are widely used for Cytological and Genetical studies?

- Easily grown in the laboratory

- Produce more number of progenies

- Can be grown in the minimal medium

- Male and female can be distinguished easily

- Limited number of chromosomes

- Can easily identify the different sets of chromosomes

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<footer style = "font-size: 18px">Parallelism between the genes and chromosomes $\rightarrow$  $\rightarrow$ <span style = "color:blue"> _Drosophila melanogaster_ </span> $\rightarrow$ Phenotypes of _Drosophila melanogastor_ $\rightarrow$ Linkage and crossing over </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Linkage and crossing over </primary>
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- The tendency of the genes present in the same chromosome to remain together and travel together from generation to generation is called linkage

- The genes located in the same chromosome are called linked genes

- Example-  The gene controlling red eye colour and grey body in Drosophila lie in the same chromosome, and are transmitted together to the next generation

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<footer style = "font-size: 18px">_Drosophila melanogaster_ $\rightarrow$ Phenotypes of _Drosophila melanogastor_ $\rightarrow$ <span style = "color:blue"> Linkage and crossing over </span> $\rightarrow$ Gene linkage and polyploidy $\rightarrow$ Unlinked genes </footer>

### <Success style="font-size:25px"> Genetics Evolution Principles Of Inheritance Variation L-7 </Success>
### <primary style="font-size:24px"> Unlinked genes </primary>
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- Unlinked genes located on different chromosomes assort differently and give a dihybrid ratio of 9:3:3:1.

- It shows a test cross ratio 1:1:1:1

- Linked genes located in the same chromosome usually do not assort independently

- They give a dihybrid ratio 3:1 and a test

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<footer style = "font-size: 18px">Linkage and crossing over $\rightarrow$ Gene linkage and polyploidy $\rightarrow$ <span style = "color:blue"> Unlinked genes </span> $\rightarrow$ Example of complete linkage $\rightarrow$ Example of complete linkage </footer>

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### <primary style="font-size:24px"> Example of complete linkage </primary>
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- In Drosophila, a homozygous red eyed and normal winged (wild type) female is crossed with double recessive male

- F1 flies are all heterozygous red eyed and normal winged

- The F1 dihybrid female fly is then test crossed with recessive male with white and vestigial wings, the progenies comprises only two types of flies - red eyed normal winged, and white vestigial winged in the ratio - 1: 1

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<footer style = "font-size: 18px">Gene linkage and polyploidy $\rightarrow$ Unlinked genes $\rightarrow$ <span style = "color:blue"> Example of complete linkage </span> $\rightarrow$ Example of complete linkage $\rightarrow$ Linkage group </footer>

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### <primary style="font-size:24px"> Example of complete linkage </primary>
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- No recombinants are formed

- It is because there is no crossing over between the linked genes

- Morgan crossed a white eyed and miniature winged female drosophila with red eyed and normal winged male

- In the F1. one red eyed and normal winged female is produced, and one white eyed miniature male is produced

- When the F1 females are inter crossed, in the F2 generation, three red eyed and normal winged progenies and one white eyed and miniature winged

- progenies are produced(3:1)

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<footer style = "font-size: 18px">Unlinked genes $\rightarrow$ Example of complete linkage $\rightarrow$ <span style = "color:blue"> Example of complete linkage </span> $\rightarrow$ Linkage group $\rightarrow$ Linkage </footer>

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### <primary style="font-size:24px"> Linkage group </primary>
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- All the genes in a particular chromosome forma linkage group

- Since the genes in a particular chromosome, have its alleles in the homologous chromosome, a pair of homologous   chromosomes are considered as a single linkage group

- So, human beings have 23 linkage groups

- Drosophila has 4 linkage groups

- Maize have 10 linkage groups

- Garden pea has 7 linkage group

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<footer style = "font-size: 18px">Example of complete linkage $\rightarrow$ Example of complete linkage $\rightarrow$ <span style = "color:blue"> Linkage group </span> $\rightarrow$ Linkage $\rightarrow$ Morgan's experiment with Drosophila </footer>

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### <primary style="font-size:24px"> Linkage </primary>
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- Traits in Morgan's cross are-

- The yellow body allele (y) is recessive to the gray body allele (y+)

- The white eyed allele (w) is recessive to the red eyed allele (w+)

- The miniature wing allele (m) is recessive to the normal winged allele (m+)

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<footer style = "font-size: 18px">Example of complete linkage $\rightarrow$ Linkage group $\rightarrow$ <span style = "color:blue"> Linkage </span> $\rightarrow$ Morgan's experiment with Drosophila $\rightarrow$ Morgan's experiment with Drosophila </footer>

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### <primary style="font-size:24px"> Morgan's experiment with Drosophila </primary>
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- In the F1, all males were white-eyed with miniature wings (wm/Y)

- All females were wild-type for eye colour and wing size red eye and normal wing (WM/wm)

- F1 produces the possible gametes (WM) (wm) (Wm) (WM)

- 25% each if independent segregation is true

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<footer style = "font-size: 18px">Linkage $\rightarrow$ Morgan's experiment with Drosophila $\rightarrow$ <span style = "color:blue"> Morgan's experiment with Drosophila </span> $\rightarrow$ Morgan's experiment with Drosophila $\rightarrow$ Morgan's experiment with Drosophila </footer>

- In F2. the most frequent phenotypes for both sexes were the phenotypes of the parents in the original cross

- white eyes with miniature wings, and red eyes with normal wings

- Non-parental phenotypes (white eyes with normal wings or red eyes and miniature wings)

- Well below the 50% predicted for independent assortment

- During meiosis alleles of some genes assort together because they are near each other on the same chromosome

- Recombination occurs when genes are exchanged between X chromosomes of the F1 females

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<footer style = "font-size: 18px">Morgan's experiment with Drosophila $\rightarrow$ Morgan's experiment with Drosophila $\rightarrow$ <span style = "color:blue"> Morgan's experiment with Drosophila </span> $\rightarrow$ Linkage in sweet pea $\rightarrow$ Linkage in sweet pea </footer>

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### <primary style="font-size:24px"> Linkage in sweet pea </primary>
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- Bateson crossed Purple, long (PPLL) x red, round (ppll) plants

- F1 offspring are purple, long (PpLI)

- F 2 - crossing PpLI × PpLI

- gametes are - PL, PI, PL, pl)

- F2 possess four different phenotypes

- In F2 generation the observed ratio is 15.6 : 1.0: 1.4:4.5

- The expected ratio 9:3:3:1

- It is not seen

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<footer style = "font-size: 18px">Morgan's experiment with Drosophila $\rightarrow$ Linkage in sweet pea $\rightarrow$ <span style = "color:blue"> Linkage in sweet pea </span> $\rightarrow$ Linkage in sweet pea $\rightarrow$ Experiment </footer>

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### <primary style="font-size:24px"> Key Points </primary>
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- Linkage between genes is detected as a deviation from expectations based on Mendel's Principle of Independent Assortment

- The frequency of recombination measures the intensity of linkage

- In the absence of linkage, this frequency is 50 percent

- For very tight linkage, it is close to zero

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<footer style = "font-size: 18px">Linkage in sweet pea $\rightarrow$ Experiment $\rightarrow$ <span style = "color:blue"> Key Points </span> $\rightarrow$ Key Points $\rightarrow$ Significance of crossing over </footer>

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### <primary style="font-size:24px"> Key Points </primary>
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- Recombination is caused by a physical exchange between paired homologous chromosomes early in prophase of the first meiotic division after chromosomes have duplicated
- At any one point along a chromosome, the process of exchange (crossing over) involves only two of the four chromatids in a meiotic tetrad 
- Late in prophase I, crossovers become visible as chiasmata. (Crossing Over)

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<footer style = "font-size: 18px">Experiment $\rightarrow$ Key Points $\rightarrow$ <span style = "color:blue"> Key Points </span> $\rightarrow$ Significance of crossing over $\rightarrow$ Homologous chromosomes </footer>

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### <primary style="font-size:24px"> Homologous chromosomes </primary>
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- **Gene loci -located on homologous chromosomes**

- Homologous chromosomes

- Duplicated homologous chromosomes

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<footer style = "font-size: 18px">Key Points $\rightarrow$ Significance of crossing over $\rightarrow$ <span style = "color:blue"> Homologous chromosomes </span> $\rightarrow$ Crossing over $\rightarrow$ Differences between monogenic inheritance and Polygenic Inheritance </footer>

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### <primary style="font-size:24px"> Differences between monogenic inheritance and Polygenic Inheritance </primary>
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- **Monogenic inheritance**

- Deals with qualitative traits

- Controlled by single pair of contrasting genes

- Phenotype shows discontinuous variation

- No intermediate phenotypes are produced

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- **Polygenic inheritance**

- Deals with quantitative traits

- Controlled by more than one pair of non-allelic genes

- Phenotype shows continuous variation

- Intermediate phenotypes are produced

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<footer style = "font-size: 18px">Homologous chromosomes $\rightarrow$ Crossing over $\rightarrow$ <span style = "color:blue"> Differences between monogenic inheritance and Polygenic Inheritance </span> $\rightarrow$ Thalassemia $\rightarrow$ Thalassemia </footer>

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### <primary style="font-size:24px"> Thalassemia </primary>
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- Antasomal recessive disorder
- Cause -  mutation / Deletion  
- Effect - reduced rate of synthesis of globin chain $\rightarrow$ Abnormal haemoglobin

- Types - $\alpha$, $\beta$ Thalassemia

- $\alpha$ Thalassemia - HbA,, Hb A<sub>2</sub> genes (- 16 chromosom) $\rightarrow$ Deletion/mutatio 
 
- $\beta$ -Thalassemia HBB gone (chromosome 11) $\rightarrow$ mutation

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<footer style = "font-size: 18px">Crossing over $\rightarrow$ Differences between monogenic inheritance and Polygenic Inheritance $\rightarrow$ <span style = "color:blue"> Thalassemia </span> $\rightarrow$ Thalassemia $\rightarrow$ Thank you </footer>