Docsity
Log inSign up
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search Store documents

The best documents sold by students who completed their studies

Search through all study resources
Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

University Rankings

Discover the best universities in your country according to Docsity users

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

From our blog

Exams and Study
Go to the blog

Meiosis and Sexual Life Cycles: Understanding the Role of Meiosis in Sexual Reproduction, Summaries of Cell Biology

Colorado Mesa University (CMU)Cell Biology

An overview of meiosis, a type of cell division essential for sexual reproduction. It explains how meiosis produces haploid gametes with unique genetic combinations, contributing to the genetic diversity of offspring. The document also discusses the importance of meiosis in the life cycles of various organisms, including humans.

Typology: Summaries

2021/2022

Uploaded on 09/12/2022

gabryel
gabryel 🇺🇸

4.6

(18)

255 documents

1 / 3

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Meiosis&and&Sexual&Life&Cycles&
by&Dr.&Ty&C.M.&Hoffman&
&
Slide&1&
Organism&reproduce&either&asexually&or&sexually.&Asexual&reproduction&requires&only&one&parent&and&
involves&cell&division&to&produce&offspring&that&are&genetically&identical&to&the&parent.&Sexual&
reproduction&involves&two&parents,&each&of&which&produces&unicellular&sex&cells&called&gametes.&A&
gamete&from&one&parent&fuses&with&a&gamete&of&the&other&parent&to&produce&a&zygote.&This&process&is&
called&fertilization.&A&zygote&carries&DNA&from&both&parents,&so&sexual&reproduction&produces&
offspring&that&are&genetically&different&from&each&other&and&from&both&parents.&Asexual&reproduction&
is&well&suited&to&organisms&that&are&very&highly&adapted&to&their&surroundings,&because&it&produces&
offspring&that&will&be&just&as&highly&adapted.&However,&the&surroundings&can&change.&Sexual&
reproduction&"shuffles&the&genetic&deck",&and&it&randomly&allows&for&certain&offspring&to&be&better&
adapted&to&surroundings&that&might&be&changing.&
&
Slide&2&
An&ordered,&pictorial&arrangement&of&an&organism's&replicated&chromosomes&(from&one&cell)&is&called&
a&karyotype.&Each&species&has&a&characteristic&number&of&different&chromosomes,&which&are&different&
from&each&other,&because&they&carry&genes&for&different&characteristics.&Ploidy&refers&to&the&number&of&
sets&of&chromosomes&contained&in&a&cell.&A&diploid&cell&is&one&that&contains&two&versions&of&each&type&
of&chromosome.&One&version&of&each&type&was&donated&by&one&of&the&organism's&parents;&the&other&
version&was&donated&by&the&other&parent.&A&haploid&cell&is&one&that&contains&just&one&of&each&type&of&
chromosome.&A&human&(like&all&animals)&contains&two&types&of&cells:&
• Somatic&cells&R&These&are&most&of&the&cells&of&the&body.&They&are&diploid,&and&when&they&divide,&
they&do&so&by&mitosis&to&produce&genetic&duplicates&of&themselves.&
• Germ&line&cells&R&These&are&specialized&cells&within&the&gonads.&They&are&diploid,&and&when&they&
divide,&they&do&so&by&meiosis&to&produce&genetically&distinct,&haploid&gametes.&&&
The&two&versions&of&each&type&of&chromosome&(one&from&each&parent)&are&homologous&to&one&
another.&Each&version&within&that&homologous&pair&is&called&a&homolog.&
&
Slide&3&
The&haploid&number&for&any&given&species&is&designated&as&N.&The&diploid&number&is&therefore&2N.&For&
any&diploid&cell,&there&are&N&homologous&pairs,&because&each&homologous&pair&is&two&chromosomes.&
&
Slide&4&
For&humans,&N=23.&Humans&are&diploid&organisms,&so&their&bodies&are&made&out&of&cells&with&46&
chromosomes&each.&When&a&human&reaches&sexual&maturity,&its&germ&line&cells&undergo&meiosis&to&
produce&haploid&gametes&(eggs&or&sperm),&each&with&23&chromosomes.&Fertilization&is&the&union&of&
two&unicellular,&haploid&gametes&to&produce&one&unicellular,&diploid&zygote.&If&two&humans&mate,&a&
sperm&and&egg&can&fuse&in&the&process&of&fertilization&to&produce&a&diploid&zygote&(46&total&
chromosomes,&23&from&each&of&the&haploid&gametes).&That&diploid&zygote&then&divides&by&mitosis&to&
produce&a&multicellular&human&of&the&next&generation,&completing&one&life&cycle.&
&
pf3

Partial preview of the text

Download Meiosis and Sexual Life Cycles: Understanding the Role of Meiosis in Sexual Reproduction and more Summaries Cell Biology in PDF only on Docsity!

Meiosis and Sexual Life Cycles

by Dr. Ty C.M. Hoffman

Slide 1 Organism reproduce either asexually or sexually. Asexual reproduction requires only one parent and involves cell division to produce offspring that are genetically identical to the parent. Sexual reproduction involves two parents, each of which produces unicellular sex cells called gametes. A gamete from one parent fuses with a gamete of the other parent to produce a zygote. This process is called fertilization. A zygote carries DNA from both parents, so sexual reproduction produces offspring that are genetically different from each other and from both parents. Asexual reproduction is well suited to organisms that are very highly adapted to their surroundings, because it produces offspring that will be just as highly adapted. However, the surroundings can change. Sexual reproduction "shuffles the genetic deck", and it randomly allows for certain offspring to be better adapted to surroundings that might be changing. Slide 2 An ordered, pictorial arrangement of an organism's replicated chromosomes (from one cell) is called a karyotype. Each species has a characteristic number of different chromosomes, which are different from each other, because they carry genes for different characteristics. Ploidy refers to the number of sets of chromosomes contained in a cell. A diploid cell is one that contains two versions of each type of chromosome. One version of each type was donated by one of the organism's parents; the other version was donated by the other parent. A haploid cell is one that contains just one of each type of chromosome. A human (like all animals) contains two types of cells:

  • Somatic cells -­‐ These are most of the cells of the body. They are diploid, and when they divide, they do so by mitosis to produce genetic duplicates of themselves.
  • Germ line cells -­‐ These are specialized cells within the gonads. They are diploid, and when they divide, they do so by meiosis to produce genetically distinct, haploid gametes. The two versions of each type of chromosome (one from each parent) are homologous to one another. Each version within that homologous pair is called a homolog. Slide 3 The haploid number for any given species is designated as N. The diploid number is therefore 2N. For any diploid cell, there are N homologous pairs, because each homologous pair is two chromosomes. Slide 4 For humans, N=23. Humans are diploid organisms, so their bodies are made out of cells with 46 chromosomes each. When a human reaches sexual maturity, its germ line cells undergo meiosis to produce haploid gametes (eggs or sperm), each with 23 chromosomes. Fertilization is the union of two unicellular, haploid gametes to produce one unicellular, diploid zygote. If two humans mate, a sperm and egg can fuse in the process of fertilization to produce a diploid zygote (46 total chromosomes, 23 from each of the haploid gametes). That diploid zygote then divides by mitosis to produce a multicellular human of the next generation, completing one life cycle.

Slide 5 All sexually reproducing species undergo a generation-­‐to-­‐generation alternation between meiosis and fertilization. This is necessary, because fertilization doubles the ploidy. Without meiosis to cut the ploidy in half again, each generation would produce cells with twice as many chromosomes as the previous generation. Animals spend most of the life cycle in the diploid condition, producing haploid gametes that exist only long enough for fertilization to occur. Fungi spend most of the life cycle in the haploid condition, as adult fungi are made of haploid cells. Since they are already haploid, they produce gametes by mitosis. Gametes fuse in fertilization to produce a diploid zygote, but that zygote immediately undergoes meiosis to produce haploid spores. These spores then undergo mitosis to produce the multicellular, haploid adult. Plants spend appreciable time in each of the two conditions. The haploid version of the plant produces gametes by mitosis (like a fungus) and is called a gametophyte. Fertilization produces a diploid zygote that undergoes mitosis to produce the diploid version of the plant, called a sporophyte, which then produces haploid spores by meiosis. Slide 6 Meiosis involves two cell-­‐division events, so the overall process is divided into meiosis I and meiosis II. Each of these is subdivided into subphases with names corresponding to the subphases of mitosis. In metaphase of meiosis I (i.e., metaphase I), N pairs of homologous, replicated chromosomes line up at the metaphase plate. This is different from metaphase of mitosis, in which 2N individual, replicated chromosomes line up. In anaphase I, the homologs in each pair separate, so that each daughter cell gets just one of the two chromosomes in each pair. Therefore meiosis I is the part of meiosis in which the ploidy is reduced from 2N to N. Meiosis II is effectively identical to mitosis, because metaphase II lines up individual, replicated chromosomes, and anaphase II separates sister chromatids. The resulting cells are gametes.