Meiosis and alternation of generations

What is sexual reproduction?

Reproduction involving meiosis and fertilization.

What is meiosis?

Nuclear division that reduces chromosome number from diploid (2n) to haploid (n).

What is fertilization?

When two haploid gametes fuse to form a diploid zygote.

What happens to chromosome number during meiosis?

it is cut in half, from 2n → n.

What is the starting cell in meiosis?

One diploid (2n) cell.

How many cells does meiosis produce?

Four haploid (n) cells.

What are the two divisions of meiosis?

Meiosis I and Meiosis II.

What is crossing-over?

Chromosomes exchange pieces of DNA, creating genetic variation.

What is independent assortment?

Chromosomes are randomly separated into cells, creating genetic variation.

What does meiosis produce in animals?

Gametes

What does meiosis produce in plants?

Spores

what is Spores

Haploid (n) cells that grow into gametophytes.

What does meiosis produce in male animals?

4 sperm cells.

What does meiosis produce in female animals?

1 ovum (egg) and 3 cells that usually die.

What is alternation of generations?

A plant life cycle that alternates between a haploid gametophyte and a diploid sporophyte.

What is a gametophyte?

The haploid (n) version/generation of a plant that produces gametes.

What is a sporophyte?

The diploid (2n) version/generation of a plant that produces spores.

How do spores grow into gametophytes?

Through mitosis.

What does the gametophyte produce?

Gametes (n).

What happens when gametes are fertilized?

They form a diploid zygote (2n).

What does the zygote grow into?

A diploid sporophyte (2n).

How does the sporophyte produce spores?

It undergoes meiosis.

: What is the order of alternation of generations?

Sporophyte (2n)
↓ meiosis
Spores (n)
↓ mitosis
Gametophyte (n)
↓ produces
Gametes (n)
↓ fertilization
Zygote (2n)
↓ mitosis
Sporophyte (2n)

What are bryophytes?

Non-vascular plants such as mosses, liverworts, and hornworts.

Which generation is dominant in bryophytes?

The gametophyte

What does the bryophyte sporophyte depend on?

The gametophyte for nutrition.

What are gymnosperms?

Seed-producing plants with “naked” seeds, usually not enclosed in fruit.

What are angiosperms?

Flowering plants whose seeds are enclosed in a fruit.

What is the gametophyte in angiosperms?

Very small and highly reduced, mainly represented by the pollen grain and embryo sac.

What are the three general types of life cycles?

Zygotic

gametic

sporic.

Which life cycle do plants have?

Sporic

What is asexual reproduction?

Reproduction that produces genetically identical or nearly identical individuals from one parent

What are examples of asexual reproduction in plants?

Root suckers

runners

stump sprouts

leaf sprouts.

What is a root sucker?

A new shoot that grows from a plant's roots.

What is a runner?

A stem that grows along the ground and produces new plants.

What is a stump sprout?

New growth that develops from a cut tree stump.

What is the advantage of sexual reproduction?

1. Genetic variation 🧬
   Offspring are genetically different from their parents and each other.

2. Better adaptation 🌎
   Variation gives some individuals traits that may help them survive environmental changes.

3. Greater disease resistance 🦠
   Genetic differences mean a disease that harms some individuals may not affect everyone the same way.

What is a disadvantage of sexual reproduction?

slower + more energy + needs fertilization.

What is the biggest advantage of asexual reproduction?

fast + less energy + no mate needed.

What is the biggest disadvantage of asexual reproduction?

• Less genetic diversity 🧬
  Offspring are usually genetically very similar to the parent.

• More vulnerable to disease 🦠
  If one plant is susceptible to a disease, many of its genetically similar offspring may also be susceptible.

• Less ability to adapt to changes 🌎
  If the environment changes, there may not be enough genetic variation to help some offspring survive.