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Life cycles of sexually reproducing organisms

Fertilization and meiosis alternate in sexual life cycles . What happens between these two events depends on the organism. The process of meiosis reduces the chromosome number by half. Fertilization, the joining of two haploid gametes, restores the diploid condition. There are three main categories of life cycles in multicellular organisms: diploid-dominant    , in which the multicellular diploid stage is the most obvious life stage, such as with most animals including humans; haploid-dominant    , in which the multicellular haploid stage is the most obvious life stage, such as with all fungi and some algae; and alternation of generations    , in which the two stages are apparent to different degrees depending on the group, as with plants and some algae.

Diploid-dominant life cycle

Nearly all animals employ a diploid-dominant life-cycle strategy in which the only haploid cells produced by the organism are the gametes. Early in the development of the embryo, specialized diploid cells, called germ cells    , are produced within the gonads, such as the testes and ovaries. Germ cells are capable of mitosis to perpetuate the cell line and meiosis to produce gametes. Once the haploid gametes are formed, they lose the ability to divide again. There is no multicellular haploid life stage. Fertilization occurs with the fusion of two gametes, usually from different individuals, restoring the diploid state ( [link] ).

This illustration shows the life cycle of animals. Through meiosis, adult males produce haploid (1n) sperm, and adult females produce haploid eggs. Upon fertilization, a diploid (2n) zygote forms, which, through mitosis and cell division, grows into an adult.
In animals, sexually reproducing adults form haploid gametes from diploid germ cells. Fusion of the gametes gives rise to a fertilized egg cell, or zygote. The zygote will undergo multiple rounds of mitosis to produce a multicellular offspring. The germ cells are generated early in the development of the zygote.

Haploid-dominant life cycle

Most fungi and algae employ a life-cycle type in which the “body” of the organism—the ecologically important part of the life cycle—is haploid. The haploid cells that make up the tissues of the dominant multicellular stage are formed by mitosis. During sexual reproduction, specialized haploid cells from two individuals, designated the (+) and (−) mating types, join to form a diploid zygote. The zygote immediately undergoes meiosis to form four haploid cells called spores. Although haploid like the “parents,” these spores contain a new genetic combination from two parents. The spores can remain dormant for various time periods. Eventually, when conditions are conducive, the spores form multicellular haploid structures by many rounds of mitosis ( [link] ).

Art connection

This illustration shows the life cycle of fungi. In fungi, the diploid (2n) zygospore undergoes meiosis to form haploid (1n) spores. Mitosis of the spores occurs to form hyphae. Hyphae can undergo asexual reproduction to form more spores, or they form plus and minus mating types that undergo nuclear fusion to form a zygospore.
Fungi, such as black bread mold ( Rhizopus nigricans ), have haploid-dominant life cycles. The haploid multicellular stage produces specialized haploid cells by mitosis that fuse to form a diploid zygote. The zygote undergoes meiosis to produce haploid spores. Each spore gives rise to a multicellular haploid organism by mitosis. (credit “zygomycota” micrograph: modification of work by “Fanaberka”/Wikimedia Commons)

If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce?

Questions & Answers

A plant is a living thing that grows in the earth and has a stem, leaves, and roots
Bello Reply
what is a plant
dalitso Reply
A plant is a living thing that grows in the earth and has a stem, leaves, and roots
Bello
a plant is an is a living thing that is classified under autothrops because it makes its own food through the process of photosynthesis .
Joanne
what is plant
Odion Reply
Plants are autotrophic
Baramox
Then animal are heterotrophic
Iyiola
what are organisms
Godfred Reply
the diagram below show how the blood of a human embryo flows close to the mothers blood in the placenta . which substances are represent at x in higher concentrations than at y
Joyce Reply
what is ecology
Odion Reply
what is cell
Odion
what is cell
Odion
What is a cell
Awal Reply
What are tissues
Awal
A cell is the smallest unit of living organisms.
hamidat
Tissues are group of similar cells performing a particular function.
hamidat
how to pronounce the word cyanobacteria
siva Reply
Cyano then bacteria. look that "cyano" is just like "ciyano".
hamidat
explain the term transpiration pull
Tank Reply
water is mainly " pulled" through the plant and that the driving force for this process is transpiration from the leaves .This is also referred to as the cohesion- tension -transpiration pull model transport.
Vanessa
explain TRANSIOCATION and GUTATION
Tank
what Is corona
INGIEBE Reply
My brother go and ask GOOGLE😷😷😷
hamidat
Google it for the right answer. Corona is a virus which causes Novel Covid-19 disease that has been declared by WHO as a global or world pandemic.
Katlholo
Why is it called Covid-19?
Katlholo
jjwhat is. condinative system
Odion
joy
Odion
condinative system is the system that harmonize all the. different. part. of. the. body and make. them function as a. specific unit
Odion
Describe the process of protein sythesis?
Kizito Reply
Ribosomes are responsible for protein synthesis in animals.
hamidat
What is a ploidy level
Francis Reply
Ploidy refers to the number of chromosomes. We have 23 pairs of chromosomes in somatic cells. Sex cells are haploid thus 23 chromosomes vs. 46 Chromosomes.
Eric
Evolution is evolvement according to one's environment. Let's use humidity as an example. A person from a very cold environment would not be used to hot humid weather. But over time their body would slowly, slowly adapt.
Eric
Give me (3) types of biodiversity
Jay
Hi guys 🇧🇪
Namutebi
hello boy
Tedi
hi
INGIEBE
yes
amani
what do you guys understand about evolution?
Kiana Reply
it's a process or analayzing some program
Fahamia
but am not sure if some know plz let share
Fahamia
is a study of
Sarah
unfolding or unrolling hence the process of development of growth
Sarah
is the periodic change of the structural features of an organism
Rahim
I think
Rahim
process of developing
Nikita
hi guiz
Mohammed
hello guys
Safuna
hi
Kaniki
Evolution ~ Is the gradual change of development over time in which a new species are formed
amani
Evolution is the sum total of adaptive changes that has existed before.
hamidat
odionjimoh
Odion
hi
Odion
why are diagrams not available
Evans Reply
How can nucleotide molecules of DNA be constructed?construct a six molecules of DNA?
Julia Reply
You take a Deoxyribose sugar. The Deoxyribose sugar has a hydrogen on the second carbon vs. an OH group. The nitrogenous base binds to the #1 Carbon and a phosphate binds to the 5'. When the 2nd NBase bonds, it does so on the 3' Carbon. Thus you have 5' to 3' directional growth.
Eric
what is the explanation of local biomes in Nigeria
Kabir
It would be savanna, tropical grassland.
Eric

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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