Chapter 6 Meiosis is the basis of sexual reproduction
What are the advantages for external fertilization?
-is not hard to get eggs and cells to unite -produce large numbers of offspring at once (good for species who have survived environmental disasters)
What are the disadvantages to external fertilization?
-millions of gametes will be released but will not survive outside the parents body they meet to result in fertilization -zygotes and embryos are unprotected outside the parent's body, they are often preyed upon -since parents don't care for their offspring, few survive to adulthood
When will cell division occur once the egg is fertilized?
-there must be enough nutrients for the rapidly diving embryo -temperature must be warm so proteins and enzymes will function properly during chemical reactions in the developing embryo -must be sufficient moisture do embryo does not dry out -embryo must be protected from predators and other environmental factors such ad ultraviolet radiation
When can chromosome mutations occur?
-when homologous chromosomes fail to separate (meiosis 1) -when sister chromatids fail to separate (meiosis 2) -result is one gamete will have 2 copies of chromosomes and the other will have no copy of that chromosome. *Chromosome mutation are not genetic*
In humans, when does embryonic development start?
In the first 2 months after fertilization
_____________discovered the laws of genetics with experiments in garden peas.
Johann Gregor Mendel
What would happen with out meiosis?
Joining of a sperm cell and a egg cell during fertilization would produce an offspring with 2 times the original number of chromosomes as it's parents. *DNA only replicates once, even cell division occurs*
What happens in meiosis 1?
Matching chromosomes called homologous chromosomes separate.
What are the 3 steps in sexual reproduction?
Mating, fertilization and development.
What is the middle layer called?
Mesoderm *Will form kidneys, muscles, blood vessels, reproductive organs and bones*
During independent assortment, how many possibilities are there for chromosomes sorting themselves into 2 daughter cells?
More than 8 million possible combinations for 23 pairs of chromosomes in egg cells and in sperm cells. When fertilization occurs, 70 trillion different zygotes are possible from the combination of a 1 sperm cell and egg cell. This is why people look different from each other.
What our the odds for a couple succeeding with IVF?
One in three
What does preventing the entrance of a sperm ensure?
Only one set of male chromosomes can unite with chromosomes in the nucleus of the cell.
What develops at 12 weeks?
Organ systems have formed
What is crossing over?
Parts of non-sister chromatids "cross over" each other and exchange segments of DNA. Each chromosome picks up new genetic information from another. Multiple crossovers can occur between chromosomes. *Crossing over creates an infinite number of genetic possibilities for just one gamete and results in variation*
What is the reproductive organ for female?
Pistil
How do plants reproduce without petals?
Plants release pollen in the air and the wind carries it to the female.
How is meiosis 1 different for males?
Produces 2 cells, immediately followed by meiosis 2 if there are enough nutrients for cell division. Result is 4 cells with the cytoplasm and organelles equally divided among them. All four cells may develop into a mature sperm.
How is meiosis 1 different for females?
Produces 2 new egg cells, but unequal division of cytoplasm and organelles. Following meiosis 2 there of the cells will disintegrate. Remaining one large egg cell with most of the cytoplasm and is available for fertilization.
What is a zygote?
Receives half the chromosomes from the female parent and half from the male parent (a fertilized egg)
What makes humans different from each other?
Receiving 23 chromosomes from each parent
Diagrams
Roughly draw them *flower from lab
What does the process of meiosis do?
Shuffles genetic information, results in variation in the gametes/gene diversity.
What happens in meiosis 2?
Sister chromatids separate.
What happens during external fertilization?
Sperm cell and egg cell unite outside the bodies of the parents.
What is internal fertilization?
Sperm cells are deposited inside female's body where the meet an egg cell. In humans more than 100 sperm cells are deposited at one time.
What is the reproductive organ for male?
Stamen
After blastula, what are cells known as?
Stem cells
What protects the embryo?
The seed's outer shell
What is pollination?
The transfer of male gametes in structures called pollen from the male reproductive part to the female reproductive part.
How are multiple births increased in in vitro fertilization?
They place more than one fertilized egg in the women, hoping one of them will grow
Why do different animals have mating seasons?
To ensure environmental conditions will be favorable.
Why is it when women undergo in vitro fertilization, they receive unpleasant side effects such as dizziness, nausea and headaches?
To help ensure the success of IVF, women receive powerful hormone treatments to increase the number of eggs she produces
What are the 3 periods differentiation is often divided into?
Trimesters (3 months long)
How many times does cell division occur in meiosis?
Twice, once at the end of meiosis 1 and meiosis 2.
What is mating?
When gametes arrive in the same place at the same time.
_______ female chromosomes
X
_______male chromosomes
Y
Can multiple crossovers occur between chromosomes?
Yes
Has ICSI been successful?
Yes about 25% of ICSI results in birth
Will genetic variation be maintained for external fertilization?
Yes, there is little chance the egg from an offspring will be fertilized by the sperm of a parent.
Can a species be better off in the environment by being sexual reproduced?
Yes,based on the combination of genes from both parents.
________trait that shows up if the gene is present like______ eyes
dominant, brown
What happens during fertilization?
egg cell is penetrated by sperm cell, haploid genetic information of both male and female gametes combines. The result is a zygote. Zygote undergoes mitosis and develops into an embryo
What is the speed of the fetus's growth at 12-16 weeks?
fetus is growing fast
What is the speed of the fetus's growth at 20-26 weeks?
fetus's growth is slowing down
Gamete
haploid reproductive cell (egg or sperm)
Haploid
having 1 set of chromsomes
Dipoild
having 2 sets of chromosomes
___________trait occurs when there is a mixed effectt
incomplete dominance
_________trait that shows up only if both genes are the same like _______eyes
recessive, blue
What is a syndrome?
A particular disease or disorder that has symptoms that occur together. With down syndrome, individuals have facial features and shorter stature ad may be prone to developing heart defects and diseases such as Alzheimer's and leukemia. 95% of diagnoses of down syndrome are caused by a copy of the 21st chromosome.
What happens after pollen lands on the female part of the plant?
A pollen tube forms (a structure that delivers sperm cells to egg cells)
What is intracytoplasmic sperm injection (ICSI)?
A single sperm cell is injected into an egg cell. The resulting zygote is inserted into the women's uterus.
What happens after fertilization for plants?
A zygote grows into an embryo and is nourished by food stored in the seed (where the embryo grows)
What is blastula?
After morula, hollow ball of cell forms
What happens during the first trimester?
All organ systems begin to develop (1-9 weeks)
Which species uses external fertilization?
Animals underwater. Often the sperm will not unite with all the eggs, the unfertilized eggs do no survive.
What is a karyotype?
Are prepared by cutting and pasting chromosomes taken from body cells during mitosis. By analyzing karyotypes, geneticists can determine when a whole chromosome mutation has occurred. Understanding which chromosomes have been affected helps physicians diagnose and treat patients with genetic disorders.
What changes can occur during meiosis?
Big changes in the organization of DNA and genes happen when pieces of chromosomes are lost duplicated or moved within a chromosome or moved to another chromosome. *They affect many genes in the chromosome and change the proteins made by those genes*
What develops at 8 weeks?
Bone cells, and the embryo is called a fetus
What develops at 4 weeks?
Brain and spinal cord
What do pollen grains do?
Carry the sperm in a protective case to the ovules (ovules contain eggs)
Meiosis
Cell division that produce gamete
What is differentiation?
Cell layers will eventually form the organs and tissues of a human baby
What happens in gastrula?
Cells of blastula organize themselves into 3 layers
What happens during meiosis 2?
Chemical messages then cells to begin the cell division process. Chromatids are pulled to opposite poles. Each daughter cell inherits one chromatid from each chromosome. The result is 4 haploid cells, each with half the number of chromosomes. *DNA is not replicated again before meiosis 2 begins*
What is artificial insemination (AI)
Collecting a sperm and injecting it into a female. (used for farm animals)
What does mitosis ensure?
Diploid number and the genetic information stays the same.
What is the outside layer of the gastrula called?
Ectoderm *Cells in this layer will eventually form skin and nervous system*
What happens when a sperm penetrates an egg cell?
Egg cell membrane changes in electrical charge, which produces chemical reactions that prevent any more sperm from entering the egg.
What is gamete intrafallopian transfer?
Egg is removed from a women's ovaries and combined with a sperm. The mixture is immediately injected into the women's fallopian tube so fertilization can take place in her body.
What happens in internal fertilization?
Embryo develops and is nourished inside the mother's body for a period of time. Embryo is also protected from predators
How is GIFT different from IVF?
Embryo is not produced outside a women's body
What is the early development of an organism called?
Embryonic developement
What is the inner layer called?
Endoderm *will form lungs, liver, and lining of the digestive system*
What is developed in the baby by 32 weeks (eight month)
Fat is deposited under the skin to keep the baby warm after birth
Zygote
Fertilized egg cell
For humans, what happens after fertilization?
Fertilized egg/zygote begins mitosis. By the end of the week, zygote divides many times to form a ball of cells *morula*
What is in vitro fertilization (IV)
Fertilizing an egg in a petri dish
What happens during the third trimester?
Fetus continues to grow in preparation for birth *significant growth in the brain*
Sexual Reproduction
Having young from two parents
What is another name for a matching pair of chromosomes?
Homologous chromosomes
What is independent assortment?
Homologous pairs of chromosomes separate at the equator and move toward opposite poles of the cell.
What is different between mitosis and meiosis 1?
In meiosis 1, the homologous chromosomes separate and move to opposite poles of the cell. 2 daughter cells result from meiosis 1.
What is the weight and size of the fetus at the end of the second trimester?
650 grams and 35 cm long
Around how many couple in America are infertile?
15%
When can the mother feel the fetus moving?
20 weeks
At nine weeks what is the weight and size of fetus? (end of first trimester)
28 grams and 9 cm long
What is the weight and size of the baby at the end of the third trimester?
3300 grams and 40-50 cm long
How long does differentiation last?
38 weeks
