What is Sexual Reproduction?
Sexual reproduction is the process by which two parents each contribute a haploid gamete that fuse at fertilization to form a genetically unique offspring. It is the dominant reproductive strategy in animals, plants and fungi because it generates genetic variation.
Sexual reproduction combines genetic material from two parents through the fusion of haploid gametes (egg and sperm) produced by meiosis, producing offspring that are genetically distinct from either parent.
- •Requires two parents
- •Gametes fuse at fertilization
- •Offspring are genetically unique
- •Gametes are produced by meiosis (haploid)
- •Population grows more slowly
- •Higher genetic variation aids adaptation
- •Requires only one parent
- •No gamete fusion occurs
- •Offspring are genetically identical clones
- •New individuals are produced by mitosis
- •Population can grow very quickly
- •Lower genetic variation, less adaptable
Step-by-step worked examples
In humans (2n = 46), how many chromosomes does each gamete carry after meiosis, and how many does the zygote have after fertilization?
Diploid number: 2n = 46 chromosomes Meiosis I and II reduce the chromosome number by half Each haploid gamete carries n = 23 chromosomes Fertilization combines 23 (egg) + 23 (sperm) = 46 chromosomes in the zygote
Due to independent assortment alone, how many genetically different gametes can one human produce?
Humans have 23 pairs of homologous chromosomes Each pair can align two possible ways during meiosis I Number of combinations = 2^n = 2^23 2^23 = 8,388,608 genetically different possible gametes from independent assortment alone
Two heterozygous pea plants (Aa x Aa) are crossed. What genotype and phenotype ratios result in the offspring?
Each parent produces A and a gametes in equal proportion Punnett square combinations: AA, Aa, Aa, aa Genotype ratio: 1 AA : 2 Aa : 1 aa If A is dominant, phenotype ratio is 3 dominant : 1 recessive
Flashcards
Quick quiz
Q1.What is produced when a haploid sperm fuses with a haploid egg?
Q2.Which cell division process produces gametes?
Q3.What is the main advantage of sexual reproduction over asexual reproduction?
Q4.In humans, how many chromosomes does a haploid gamete contain?
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Common mistakes
Thinking gametes are diploid like body cells. — Correct: Gametes are haploid (n) - they carry half the chromosome number of body cells, which are diploid (2n).
Believing sexual reproduction always requires two separate organisms. — Correct: Most sexually reproducing species need two parents, but some organisms (like many plants and hermaphroditic animals) can self-fertilize while still using meiosis and fertilization.
Confusing fertilization with mitosis. — Correct: Fertilization is the fusion of two gametes; the resulting zygote then divides by mitosis to grow into an embryo.
Assuming offspring are identical to their parents in sexual reproduction. — Correct: Because gametes are genetically variable and fuse randomly, sexually produced offspring are genetically unique, not identical to either parent.
FAQ
What is sexual reproduction?
Sexual reproduction is the fusion of haploid gametes from two parents at fertilization to create genetically unique offspring.
What is the difference between sexual reproduction and asexual reproduction?
Sexual reproduction needs two parents and gamete fusion, producing genetically varied offspring; asexual reproduction needs one parent and mitosis, producing identical clones.
What are some examples of sexual reproduction?
Human reproduction (sperm and egg fusion), flowering plant pollination, and external fertilization in fish and frogs are all examples of sexual reproduction.
How does sexual reproduction increase genetic variation?
Through independent assortment and crossing over during meiosis, plus the random combination of two different parents' genes at fertilization.