Class 10 Science – Heredity and Evolution
Topic: Dihybrid Cross
Question:
In pea plants, round seed shape (R) is dominant over wrinkled seed shape (r) and yellow seed colour (Y) is dominant over green seed colour (y).
A homozygous round yellow plant (RRYY) is crossed with a homozygous wrinkled green plant (rryy).
1. Write the genotype and phenotype of F₁ generation.
2. Perform the cross to obtain F₂ generation.
3. Write the phenotypic ratio of F₂ generation.
4. Name the law illustrated by this cross.
Solution:
Step 1: Parent Generation (P)
Round Yellow = RRYY
Wrinkled Green = rryy
Gametes:
RRYY → RY
rryy → ry
Step 2: F₁ Generation
RY × ry
All offspring = RrYy
F₁ Genotype = RrYy
F₁ Phenotype = Round Yellow (because R and Y are dominant)
Step 3: F₁ Self Cross
RrYy × RrYy
Gametes formed by each parent:
RY, Ry, rY, ry
Punnett Square:
RY Ry rY ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
Step 4: F₂ Phenotypic Ratio
Round Yellow = 9
Round Green = 3
Wrinkled Yellow = 3
Wrinkled Green = 1
Phenotypic Ratio = 9 : 3 : 3 : 1
Step 5: Law Illustrated
This cross explains Mendel’s Law of Independent Assortment, which states that inheritance of one trait is independent of inheritance of another trait.
Topic: Dihybrid Cross
Question:
In pea plants, round seed shape (R) is dominant over wrinkled seed shape (r) and yellow seed colour (Y) is dominant over green seed colour (y).
A homozygous round yellow plant (RRYY) is crossed with a homozygous wrinkled green plant (rryy).
1. Write the genotype and phenotype of F₁ generation.
2. Perform the cross to obtain F₂ generation.
3. Write the phenotypic ratio of F₂ generation.
4. Name the law illustrated by this cross.
Solution:
Step 1: Parent Generation (P)
Round Yellow = RRYY
Wrinkled Green = rryy
Gametes:
RRYY → RY
rryy → ry
Step 2: F₁ Generation
RY × ry
All offspring = RrYy
F₁ Genotype = RrYy
F₁ Phenotype = Round Yellow (because R and Y are dominant)
Step 3: F₁ Self Cross
RrYy × RrYy
Gametes formed by each parent:
RY, Ry, rY, ry
Punnett Square:
RY Ry rY ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
Step 4: F₂ Phenotypic Ratio
Round Yellow = 9
Round Green = 3
Wrinkled Yellow = 3
Wrinkled Green = 1
Phenotypic Ratio = 9 : 3 : 3 : 1
Step 5: Law Illustrated
This cross explains Mendel’s Law of Independent Assortment, which states that inheritance of one trait is independent of inheritance of another trait.
Notes for the Day ✌️
❁ In some plants sepals of the flower 🌹 remain attached after fertilisation during embroygenesis. E.g., Tomato 🍅, Brinjal, Strawberry 🍓.
❁ The zygote develops into embryo after which the ovule becomes the seed and ovary becomes the fruit 🍏
❁ Inside the mature seed is the progenitor of the next generation, the embryo. 🙌
❁ The fruit develops a thick wall called pericarp that is protective in function.🔥
❁ After dispersal, seeds🌱 germinate under favourable conditions to produce new plants. 🌾
❁ In some plants sepals of the flower 🌹 remain attached after fertilisation during embroygenesis. E.g., Tomato 🍅, Brinjal, Strawberry 🍓.
❁ The zygote develops into embryo after which the ovule becomes the seed and ovary becomes the fruit 🍏
❁ Inside the mature seed is the progenitor of the next generation, the embryo. 🙌
❁ The fruit develops a thick wall called pericarp that is protective in function.🔥
❁ After dispersal, seeds🌱 germinate under favourable conditions to produce new plants. 🌾
❤1
1 Mark Questions (Very Expected)
1. Define capacitation.
→ Functional changes in sperm inside female reproductive tract to fertilize ovum.
2. What is colostrum?
→ First milk produced after childbirth, rich in antibodies.
3. Name the hormone responsible for ovulation.
→ LH (Luteinizing Hormone)
4. What is parturition?
→ Process of childbirth.
5. Name the site of fertilization in humans.
→ Ampullary-isthmic junction of fallopian tube.
6. What is amniocentesis? Why is it banned?
→ Prenatal sex determination technique; banned to prevent female foeticide.
2 Marks Questions
Q1. Differentiate between spermatogenesis and oogenesis.
Spermatogenesis
Oogenesis
Occurs in testes
Occurs in ovaries
Produces 4 sperms
Produces 1 ovum
Starts at puberty
Starts before birth
Q2. Write functions of placenta.
Supplies oxygen and nutrients
Removes waste
Secretes hormones (hCG, hPL, estrogen, progesterone)
Q3. What are the major events of menstrual cycle?
Menstrual phase
Follicular phase
Ovulation
Luteal phase
3 Marks Questions (Highly Important)
Q4. Draw and label human male reproductive system.
Very frequently asked.
Focus labels:
Testis
Epididymis
Vas deferens
Seminal vesicle
Prostate gland
Penis
Urethra
Q5. Draw and label female reproductive system.
Important labels:
Ovary
Fallopian tube
Uterus
Cervix
Vagina
Q6. Explain menstrual cycle briefly.
Prepare full explanation with 4 phases + hormone role.
Q7. What are the different methods of contraception?
Natural methods
Barrier methods
IUDs
Oral pills
Surgical methods
Q8. Explain test tube baby programme (IVF).
Steps:
Ovum collection
Sperm collection
Fertilization outside body
Embryo transfer
5 Marks Questions (Most Expected)
Q9. Describe the process of fertilization and implantation.
Must prepare in sequence:
Sperm reaches ampullary-isthmic junction
Acrosomal reaction
Fusion of gametes
Zygote formation
Cleavage
Blastocyst
Implantation
Q10. Explain events of pregnancy till parturition.
Includes:
Implantation
Placenta formation
Hormonal support
Foetal development
Parturition
Q11. What are STDs? Mention symptoms, causes and prevention.
Examples:
AIDS
Gonorrhoea
Syphilis
Prevention:
Safe sex
Hygiene
Avoid multiple partners
Regular medical check-up
Q12. Explain population explosion and birth control measures.
Very common from reproductive health.
Most Important Diagrams
Prepare these perfectly:
✅ Male reproductive system
✅ Female reproductive system
✅ Structure of sperm
✅ Graafian follicle
✅ Blastocyst
1. Define capacitation.
→ Functional changes in sperm inside female reproductive tract to fertilize ovum.
2. What is colostrum?
→ First milk produced after childbirth, rich in antibodies.
3. Name the hormone responsible for ovulation.
→ LH (Luteinizing Hormone)
4. What is parturition?
→ Process of childbirth.
5. Name the site of fertilization in humans.
→ Ampullary-isthmic junction of fallopian tube.
6. What is amniocentesis? Why is it banned?
→ Prenatal sex determination technique; banned to prevent female foeticide.
2 Marks Questions
Q1. Differentiate between spermatogenesis and oogenesis.
Spermatogenesis
Oogenesis
Occurs in testes
Occurs in ovaries
Produces 4 sperms
Produces 1 ovum
Starts at puberty
Starts before birth
Q2. Write functions of placenta.
Supplies oxygen and nutrients
Removes waste
Secretes hormones (hCG, hPL, estrogen, progesterone)
Q3. What are the major events of menstrual cycle?
Menstrual phase
Follicular phase
Ovulation
Luteal phase
3 Marks Questions (Highly Important)
Q4. Draw and label human male reproductive system.
Very frequently asked.
Focus labels:
Testis
Epididymis
Vas deferens
Seminal vesicle
Prostate gland
Penis
Urethra
Q5. Draw and label female reproductive system.
Important labels:
Ovary
Fallopian tube
Uterus
Cervix
Vagina
Q6. Explain menstrual cycle briefly.
Prepare full explanation with 4 phases + hormone role.
Q7. What are the different methods of contraception?
Natural methods
Barrier methods
IUDs
Oral pills
Surgical methods
Q8. Explain test tube baby programme (IVF).
Steps:
Ovum collection
Sperm collection
Fertilization outside body
Embryo transfer
5 Marks Questions (Most Expected)
Q9. Describe the process of fertilization and implantation.
Must prepare in sequence:
Sperm reaches ampullary-isthmic junction
Acrosomal reaction
Fusion of gametes
Zygote formation
Cleavage
Blastocyst
Implantation
Q10. Explain events of pregnancy till parturition.
Includes:
Implantation
Placenta formation
Hormonal support
Foetal development
Parturition
Q11. What are STDs? Mention symptoms, causes and prevention.
Examples:
AIDS
Gonorrhoea
Syphilis
Prevention:
Safe sex
Hygiene
Avoid multiple partners
Regular medical check-up
Q12. Explain population explosion and birth control measures.
Very common from reproductive health.
Most Important Diagrams
Prepare these perfectly:
✅ Male reproductive system
✅ Female reproductive system
✅ Structure of sperm
✅ Graafian follicle
✅ Blastocyst