Reproduction

Reproduction involving **two parents** and the **fusion of two gametes** to form the new organism.

Reproduction involving **one parent** and **no fusion of gametes** — the offspring are genetically identical to the parent.

A **sex cell** (such as a sperm or an egg) that fuses with another gamete at fertilisation.

The **fusion of two gametes** to form a single new cell.

An organism that is **genetically identical** to its parent.

Sexual reproduction needs **two** parents; asexual reproduction needs **one**.

**Meiosis** (followed by fertilisation when the gametes fuse).

**Mitosis** only — it copies the genes exactly.

There is **one parent** and only **mitosis**, so the genome is copied exactly — no gametes, no mixing of alleles.

**Two parents** (different alleles), **meiosis** (shuffles alleles into different gametes) and **random fertilisation** (any gamete can fuse with any other).

It gives the species the **raw material for natural selection** to act on if the environment changes.

**Genetically identical** — a cutting is asexual reproduction, so the genome is copied unchanged (a clone).

An organism (or cell) that is **genetically identical** to the one it came from.

Reproduction from a **single parent**, **without gametes or fertilisation**, producing offspring genetically identical to the parent.

**Mitosis** — it copies the parent's DNA exactly, so there is **no genetic variation**.

By **budding** — a small outgrowth (bud) receives a copy of the genetic material and then **pinches off** as a smaller, identical daughter cell.

**Budding** (yeast, Hydra) and plant **runners / tubers / bulbs** (e.g. strawberry, potato).

Cloning a plant by growing a new plant from a part of the parent — e.g. a **stem cutting** encouraged to grow roots.

Take a cutting from the parent, **encourage it to grow roots**, and raise a plant **genetically identical** to the parent.

Growing **many identical plantlets** from a few cells of one plant on a sterile **nutrient medium**.

**Somatic-cell nuclear transfer (SCNT)** — it produced **Dolly the sheep**.

Take a **body-cell nucleus** → put it into an **egg whose nucleus was removed** → **stimulate** it into an embryo → **implant** in a surrogate mother.

The **adult body-cell nucleus** is kept (and transferred); the **egg's own nucleus is removed**.

**Genetically identical** to each other and the parent — they are clones made by mitosis, so there is **no variation**.

**Asexual** — it uses one parent and no fertilisation, so the offspring are clones.

A **sex cell** (sperm or egg) used in sexual reproduction. Gametes are **haploid**.

Sperm are made in the **testes**; eggs are made in the **ovaries**.

**Meiosis** — it halves the chromosome number, producing **haploid** cells.

Having **one set** of chromosomes (n). Human gametes are haploid (23 chromosomes).

Having **two sets** of chromosomes (2n) — one from each parent. Most body cells are diploid (46 chromosomes).

The **fusion of a sperm nucleus with an egg nucleus** to form a diploid zygote.

The single **diploid (2n)** cell formed when a sperm fertilizes an egg; it divides to form an embryo.

So that at fertilization the diploid number is **restored**, not **doubled** — keeping the chromosome number constant each generation.

In the **oviduct (fallopian tube)**.

Sperm are **small, many and swim** with a tail (little food); the egg is **large, few, cannot swim** and has a big **food store**.

Made in the **testis** → carried by the **sperm duct** → out through the **urethra**.

Released from the **ovary** → travels along the **oviduct** → reaches the **uterus**.

Once one sperm enters, the egg membrane **changes to block any other sperm** (preventing extra chromosomes).

**n + n → 2n** — two haploid gametes fuse into one diploid zygote.

About **28 days**.

**FSH** and **LH**.

**Oestrogen** (from the follicle) and **progesterone** (from the corpus luteum).

It **stimulates a follicle in the ovary to grow** and mature.

It **repairs and thickens the uterus lining**, and when high it **triggers the LH surge**.

A sharp **LH surge** from the pituitary, around **day 14**.

What the **empty follicle becomes** after ovulation; it secretes **progesterone**.

It **maintains the thick uterus lining** and **inhibits FSH and LH** (negative feedback).

**Progesterone falls**, the lining breaks down (**menstruation**), and a new cycle begins.

**High oestrogen stimulates the LH surge** — a high level causes a bigger release.

**Oestrogen and progesterone inhibit FSH and LH**, stopping extra follicles ripening.

**Ovulation** — the LH surge triggers the release of the egg.

**Progesterone**, made by the corpus luteum.

The **reproductive organ** of a flowering plant; it holds the male and female parts.

The **stamen** = an **anther** (makes pollen) on a **filament** (stalk).

The **carpel** = a **stigma** (catches pollen), a **style**, and an **ovary** containing **ovules**.

It **makes and holds pollen grains**, which carry the male gametes.

It is the **sticky tip** that **catches and holds pollen** grains that land on it.

The **transfer of pollen from an anther to a stigma**.

The **fusion of a male gamete with the female gamete (egg)** inside the ovule, forming a zygote.

**Pollination** first (pollen onto the stigma); **fertilization** second (gametes fuse in the ovule).

A **pollen tube grows down the style** from the pollen grain, carrying the male gamete to the ovule.

A **seed** (containing the embryo and a food store).

A **fruit**, which surrounds the seeds and helps disperse them.

Alleles that make a plant's stigma **reject its own pollen**, so it cannot fertilise itself.

They **force cross-pollination**, which **increases genetic variation** in the offspring.

Plants that **cannot fertilise themselves** — e.g. those with self-incompatibility or with male and female parts that mature at different times.