Sexual reproduction and Meiosis Flashcards
What are the two processes of sexual reproduction
-Formation of gametes
-Fertilization of gametes to form zygote
What are gametes
Sex cells, sperm and eggs
What are zygotes
Cells made by fussion of sex cells
What are the reproductive organs in animals and what do they make
-Testes (Make sperm)
-Ovaries (Make ova)
What happens to the number of chromosomes when sperm and egg fuse
They become diploid, 46 chromosomes
What is meiosis
A 2 stage cell division where the resulting daughter cells have half the number of chromosomes
Why does meiosis result in half the number of chromosomes?
Because meiosis results in the making of gametes
How many chromosomes does mitosis end in and how many chromosomes does meiosis end with
Mitosis ends with 46 body cells
Meiosis ends with 23 sex cells
why are gametes called the haploid number?
Because they are half the number of chromosomes in the body cells
What are homologous chromosomes
-We recieve one from each parent
-carry information for the same genes
-Same size and shape unless X and Y chromosomes (determine the sex)
In mitosis there is one cell division, how many cell divisions does meiosis go through
2
How many daughter cells are produced at the end of meiosis
4 haploid cells
What are the two meiosis stages called
Meiosi 1 and meiosis 2
What are the phases in meiosis 1
Interphase, prophase 1, metaphase 1, anaphase 1 and telophase 1
What are the phases in meiosis 2
Prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokenisis
What happens during interphase in meiosis
DNA is replicated to make a tetrad
What is a tetrad
A pair of homologous chromosomes (One from each parent)
What happens during Prophase 1
-Chromosomes shorten and thicken
-Genetic information “crosses over” from both homologous chromosomes
-Nuclear membrane dissolves
-Spindle fibres form and centrioles go to opposite sides
What happens in metaphase 1
-Spindle fibres attach to the centromeres of the chromosomes
-Line up in the middle of the cell
What happens in anaphase 1
-Spindle fibres pull tetrads apart
-Homologous pairs move to opposite sides
What happens in telophase 1
-The cell divides into two
-Spindle fibres disappear
-Nuclear membrane forms
-Each daughter nucleus gets 1 member of the og chromosome pair
What happens in prophase 2
-No DNA duplication
-Each cell has 46 chromosomes
-Spindle fibres form
-Nuclear membrane dissolves
What happens in metaphase 2
-Sister chromatids line up in the middle of the cell
What happens in Anaphase 2
Sister chromatids seperate to opposite sides
What happens in telophase 2
-Cell begins to pinch in
-Spindle fibres disappear
-Nuclear membrane reforms
What happens in cytokenisis
Makes 4 cells, each have haploid number of chromosomes
Why are humans so unique from one another
Because there are so many different possible combinations of chromosomes during meiosis
What is gametogenesis
Production of gametes in animals
What produces sperm in animals
Spermatogenesis
What produces ova in animals
Oogenesis
In spermatogenesis how many sperm cells do we get
4
Are the sperm cells different or equal in size
Same size
In Oogenesis, does cytoplasm divide equally
No, some cells get more cytoplasm than others
What are cells that dont recieve enough cytoplasm during oognesis called and why
Polar bodies because they die
How many ova is produced in oogenesis
1 ovum
What are sex chromosomes
Chromosomes that are different in men and women of the same species
What are the human sex chromosomes of women
XX
What are the human sex chromosomes of men
XY
If sex chromosomes are chromosomes, why are they not considered honologous pair?
Because Y is smaller than X
Can something go wrong in meisis for the chromosomes to not seperate properly
Yes
What is non disjunction
When homologous chromosomes fail go seperate during meiosis
What happens when non disjunction happens
One cell has an extra chromosome or one cell is missing a chromosome (22 or 24 chromosomes)
What happens if a gamete with 24 chromosomes combines with a gamete with normal 23 chromosomes
It will have 47 chromosomes, will lead to a genetic problem
What is trisomy
When there are 3 homologous chromosomes instead of a pair
What is monosomy
When there is 1 chromosome instead of a pair
How do we diagnose non-disjunction
using a Karyotype
What is a karyotype
A picture of all chromosomes organized by size, number and shape
In karyotypes, humans have ___ pairs of autosomes and ___ pair of sex chromosomes
22 pairs of autosomes (body chromosomes)
ane 1 pair of sex chromosomes
What disorder is it when there is only 1 X chromosome
Turner syndrome (affect women)
What disorder is it when there are 2 X chromosomes and 1 Y chromosome
Klinefelter syndrome (Affect men)
What disorder is it when there are 3 chromosomes in chromosome 13
Patau syndrome, trisomy of chromosome 13
What disorder is it when there are 3 chromosomes in chromosome 18
Edwards syndrome, trisomy of chromosome 18
What disorder is it when there are 3 chromosomes in chromosome 21
Down syndrome, trisomy of chromosome 21
How does a daughter cell compare to the parent cell after meiosis
It is different than the parent
What process in prophase 1 makes every gamete different
Crossing over
Why does a chromosome have two sister chromatids
Because each chromosome was duplicated during S phase
