• Male

• Female

• Eggs

• Sperm

Female & Male

• X Chromosome

• Y Chromosome

• Sex Chromosome

• Types of gametes

• Male produces sperms with A+Y & A+X

• (Male - heterogamy)

• Androsperms(A+Y)& Gynosperms(A+X)

• Female produces ovum with A+X only

• Female homogamy

• It is seen in unisexual plants also

• Example Melandrium album

• Sperm with A+X fuses with A+X ovum,

• Progeny is- AA+XX - Female

• Sperm with A+Y fuses with A+X ovum,

• Progeny is- AA+XY - Male

• Seen in some insects

• Eg-cockroaches,grasshoppers,bugs

• Female is homogametic with two homomorphic X chromosomes

• Male is heterogametic

• Male is- XO with one sex chromosome only

• Male produces A+X & A+0 gametes

• Male heterogamy

• Female produces A+X gametes only

• Female is homogametic

• A+X sperm fuses with A+X ovum,the progeny is-AA+XX Female

• A+0 sperm fuses with A+X ovum the progeny is – Male

• Seen in butterflies, moths,fishes birds, reptiles

• Male is homogametic with two homomorphic chromosomes - ZZ

• Female is heterogametic with two heteromorphic chromosomes –ZW

• Male produces A+Z sperms only

• Female produces A+Z & A+W eggs

• A+Z sperm fuses with A+Z egg progeny is male (AA+ZZ)

• A+Z sperm fuses with A+W egg, progeny is female (AA+ZW)

• Seen in certain butterflies

• Female is heterogametic- produces two types of gametes-A+z & A+0

• Male is homogametic - produces A+Z type sperms only

• A+Z sperm fuses with A+Z ovum, the progeny is AA+ZZ- Male

• A+Z sperm fuses with A+0 ovum, progeny is Female

• Seen in bees, wasps,saw flies,ants

• Unfertilised egg developes into - male

• Fertilised egg developes into female

• Female is diploid (2n)

• Male is haploid (n)

• Sperms are produced by mitosis

• Ovum is produced by meiosis

• Here sex is determined by number of set of chromosomes

Sex determination in honey bees

• Male honey bee has n = 16 chromosomes

• Female Honey bee has 2n = 32 chromosomes

• Male honey bee produces gametes by mitosis

• Female honey bee produces gametes by meiosis

• Male and female gametes fuses and produces 2n = 32 i.e. female honey bee

• diploid female bee(meiosis)$\rarr$ eggs $\rarr$ no fertilisation $\rarr$haplodid female bee

• diploid female bee(meiosis)$\rarr$ eggs $\rarr$fertilisation $\rarr$diploid male bees

• haplodid male bees(no meiosis)$\rarr$ sperms $\rarr$ fertilisation $\rarr$daplodid female bee

• Egg with n = 16 without fertilisation develops into male honey bee

• So male honey bees do not have father

• Male honey bees can’t produce son

• Male honey bee has only mother

• A gene produces multiple phenotypic effect

• Eg: The genes that control flower colour in sweet pea also control colour of the seed coat and red spots in axils of the leaves

• In Drosophila the gene for wing size also controls eye colour and fertility

• Pleiotropy is seen in human diseases called sickle cell anaemia

• The gene alter the type of haemoglobin and also change the shape of RBCs

In pea plants synthesis of starch is controlled by a single gene with alleles;

• BB produces large starch grains

• Bb produces intermediate starch grains

• bb produces smaller starch grains

• The same gene controls the shape of the seed

• BB genes produces round seed

• Bb genes produces round seed

• bb genes produces wrinkled

• Bb genes shows incomplete dominance in the production of starch grain.

• It is also known as quantitative inheritance or multiple genic inheritance or cumulative gene effect

• A character is controlled by many genes

**Eg:**Skin colour in human, height in individual, hair colour, weight, intelligence, milk production in cattle, egg laying in chicken, etc

• A character controlled by many genes is known as polygenic character

• Each dominant gene shows additive effect or cumulative effect in the production of the phenotype

• Controlled by 3 separate pairs of gene

• Represented as Aa, Bb, Cc located on different chromosomes

• They are inherited independently

• A, B, C controls dark colour of the skin

• The dark colour of the skin is proportionate to the number of dominant genes present

• A pure negro has 6 dominant genes for skin colour

• AA BB CC

• A pure white has 6 recessive genes for skin colour

• aa bb cc

• A cross between pure negro and pure white produces F₁ hybrid offspring with the genotype Aa Bb Cc

• The phenotype is known as mulatto

• The skin colour is intermediate between both the parents

• In the F₂ generation there are 64 combinations

• The skin colour ranges from pure black (negro) to pure white with so many gradations.

• Pure black or negro : 1/64

• Very dark brown : 6/64

• Dark brown : 15/64

• Mulatto : 20/64

• Light brown : 15/64

• Very light brown : 6/64

• Pure white : 1/64

• The F₂ phenotypic ratio in polygenic inheritance is 1:6:15:20:15: 6:1

• Sir Francis Galton first studied the polygenic inheritance

• Study of family history about the inheritance of a trait in humans

• It is done for many generations

• It is represented in family tree using some symbols

• Controlled breeding experiments are not possible in humans

• Mendelian disorders are traced in a family by Pedigree analysis

• Example- Cystic fibrosis,sickle celled anaemia, Phynyl ketonurea, Thalesemia,colour blindness, Haemophilia

• Both sexes are involved

• Generation not skipped

• “Vertical” transmission

• Spontaneous mutation

• 50% risk for affected child, if parent affected

• Male is represented by Square

• Female is represented by circle

• Affected individual is represented by Shading

• Carriers are denoted by symbol with dot

• Symbol with number shows the number of the progenies

• Line between the parents is the mating line

• Double line between the parents shows the consanguineous marriage

• Bleeders disease

• Caused by recessive gene seen in the X chromosome

• Blood of the patient lacks anti haemophilic globulin

• Causes profussive bleeding

• Reported first in Queen Victoria

• Carriers transmit this disease to son

• From son to grand daughter

• The gene for haemophilia moves in a zig zag manner. So called criss-cross inheritance

• Even a minute injury causes heavy bleeding

• It is an example of sex linked inheritance

• The gene for sex linked inheritance is linked to X chromosome