Class notes for class 10

P HEREDITY
W
TRANSMISSION
TRANSMISSION OF CHARACTERS
OF CHARACTERS FROM
FROM ONE ONE GENERATION
GENERATION TO ANOTHER
TO ANOTHER GENERATION
Traits

Genetic variation v/s Variations Rules for Inheritance Inherited traits Acquired traits
Environmental variation Differences present between Seven visible traits chosen by Gregor Mendel
Traits or variants
the individuals of same Character Dominant Trait Recessive Trait Phenotypic/ physical Culinary
that genes encode
Genetic variation Environmental variation species or different species. features influenced by
Seed shape Round Wrinkled in DNA and pass Music Art
is the variation of is the alteration of the Significance in Sexual environmental factors
from parent to
genomes between phenotype of a part- Reproduction: Seed colour Yellow Green and are not inherited by
off-spring during
individuals in the icular genotype as a • Creates genetic diversity. the next generation. Video Sport
Flower colour Purple White reproduction. games
same species. response to the • Increases survival chances. Examples: Ear piercing,
Pod shape Inflated Constricted Example: Hair colour,
environment. • Leads to evolution. building muscles,
Pod colour Green Yellow skin colour, eye
• Helps in natural selection. riding bicycle, scars etc.
Examples: Examples: Phenotypic colour etc.
Flower position Axial Terminal
Coat colors of differences in identical
animals, skin color, twins. Stem length Tall Dwarf
hair color, color of
eyes, freckles, and
dimples.
Monohybrid Cross Dihybrid Cross
Key Terms A cross in which the traits of aParental
single characteristic are studied. The cross between two different
Generation genes that differ in two observed Parental Round Yellow Wrinkled Green

X
traits. RR YY rr yy
• Allele Different forms of a gene Generation
(e.g., T and t for height).
Parental Generation F1 Generation
47




• Dominant Express itself even in Gametes RY ry
TT tt
heterozygous condition. Genotype All are RrYy.
Gametes T t Round Yellow
• Recessive Express only in homozygous Rr Yy
T t Phenotype All are round & yellow.
condition.
Tt Self-pollination
• Genotype The genetic makeup (e.g., TT, F1 Generation
Tt, or tt). Genotype All are Tt. X
Self
pollination RY RY
• Phenotype The physical expression of the Phenotype All are tall.
trait (e.g., tall or short). Gametes F2 Generation Gametes rY rY Gametes
T t T t RRYY

Genotype RRYY:RRYy:RrYY:RrYy: Ry Ry
• Homozygous Both alleles are the same T T RrYY RrYY
TT RRyy: Rryy:rrYY:rrYy: ry
(TT or tt). ry
t Tt Tt t rryy = 1 :2 :2 :4 :1 :2 :1 :2 :1
RRYy rrYY RRYy

• Heterozygous Alleles are different (Tt) tt RrYy RrYy RrYy RrYy
F2 Generation Phenotype Round Yellow: Round
rrYy RRyy rrYy
Green: Wrinkled Yellow:
Genotype TT : Tt : tt = 1 : 2 : 1
Wrinkled Green = 9:3:3:1 Rryy Rryy
Phenotype Tall : Dwarf = 3 : 1
rryy
TT Tt Tt tt



e Sex Determination
ch
Xosom
Sp
erm ro X
m Ovum
os m
chr om ro Human females (XX) produce all gametes (ova) with X-chromosomes, while human male (XY) produce 50% gametes (sperms) with X-chromosome while 50%
om Y e ch X som e
oso mo
gametes with Y chromosome. If sperm having X chromosome fertilises the ovum with X chromosome, then a female child will be produced, otherwise a male child
me chro will be produced.
XY XX

• Temperature-Dependent Sex Determination: In reptiles like turtles and crocodiles, higher incubation temperatures (females), and while lower temperatures males
• Sex Change by Environmental Cues: Some fish and snails can change sex during their lifetime
XY XX