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Bio 100 (part 3) > Meiosis > Flashcards

Flashcards in Meiosis Deck (24):
1

What is the goal of Meiosis?

Goal: begin with a normal cell (2 copies of each chromosome) and end with a cell that has half the genetic content (1 copy of each chromosome) and is genetically unique.

2

Mitosis

Mitosis—new daughter cells are generated.
Produces identical cells
DNA is doubled during the process, and then divided to an identical amount.
For growth and replacement.

3

Meiosis

Meiosis--gametes are generated for sexual reproduction.
Produces cells that differ genetically.
Hereditary information reduced by one half.
For producing reproductive cells (gametes).
reduction division
division that halves the chromosome number
a diploid cell (in an ovary or testes) divides to produce haploid cells, gametes

4

How many chromosomes does a haploid have?

23 chromosomes for humans
(1n = 23 for humans)
possessing a single version of each chromosome type

5

How many chromosomes does a Diploid have?

46 chromosomes for humans
(2n = 46 for humans)
possessing two versions of each chromosome type

6

Which of the following statements about homologous chromosomes is incorrect?
A. Each chromosome has the same genes in the same order (X and Y is the exception)
B. One is inherited from the male parent and the other from the female
C. Each consists of two sister chromatids after the S phase of mitosis
D. Are the same in terms of DNA nucleotide composition

D. Are the same in terms of DNA nucleotide composition

7

Define gametes

Produced by special cells in ovaries and testes
sex cells such as eggs and sperm.
haploid, 1n chromosomes (one of each chromosome), ½ the amount of DNA
formed by meiosis

8

Define somatic cells

All other body cells in an organism
diploid in most, 2n chromosomes (two of each chromosome), full amount of DNA
formed by mitosis

9

Define Allele

Versions of a gene coding for a particular protein

10

Understand the term tetrad

Tetrad: a pair of homologous, duplicated chromosomes

11

How many sister chromatids are there in a tetrad?

4

12

What is crossing over?

The chromosomes exchange pieces of themselves to the other chromosome from the paternal and maternal chromosomes
This is the

13

Consequences of crossing over

Crossing over in the first phase of meiosis
At least one cross over in all 23 pair (several in the larger chromsomes)
Nearly infinite variation possible for the gametes produced

14

Consequences of Independent assortment

Independent assortment in the first phase of meiosis
each tetrad moves to the metaphase I plate independently of the other tetrads
the total number of possible outcomes = 2n (n = number of haploid chromosomes)
2^23 for humans, 8.4 million different ways (different gametes)

15

Explain why meiosis is called “reduction division,” and why it is necessary for gamete formation.

formation of gametes that are going to join in fertilization requires a reduction of the genetic material to ½
besides crossing over and independent assortment, meiosis reduces the number of chromosomes from 2 of each type to 1 of each type (2n to 1n, diploid to haploid)
otherwise, every generation would double the amount of homologous genetic information

16

Explain why meiosis is called “reduction division,” and why it is necessary for gamete formation.

formation of gametes that are going to join in fertilization requires a reduction of the genetic material to ½
besides crossing over and independent assortment, meiosis reduces the number of chromosomes from 2 of each type to 1 of each type (2n to 1n, diploid to haploid)
otherwise, every generation would double the amount of homologous genetic information

17

Explain why meiosis is called “reduction division,” and why it is necessary for gamete formation.

formation of gametes that are going to join in fertilization requires a reduction of the genetic material to ½
besides crossing over and independent assortment, meiosis reduces the number of chromosomes from 2 of each type to 1 of each type (2n to 1n, diploid to haploid)
otherwise, every generation would double the amount of homologous genetic information

18

Explain why meiosis is called “reduction division,” and why it is necessary for gamete formation.

formation of gametes that are going to join in fertilization requires a reduction of the genetic material to ½
besides crossing over and independent assortment, meiosis reduces the number of chromosomes from 2 of each type to 1 of each type (2n to 1n, diploid to haploid)
otherwise, every generation would double the amount of homologous genetic information

19

Explain why meiosis is called “reduction division,” and why it is necessary for gamete formation.

formation of gametes that are going to join in fertilization requires a reduction of the genetic material to ½
besides crossing over and independent assortment, meiosis reduces the number of chromosomes from 2 of each type to 1 of each type (2n to 1n, diploid to haploid)
otherwise, every generation would double the amount of homologous genetic information

20

In meiosis in males, the X and Y chromosomes are mostly not homologous (don’t have the same genes) so there is essentially no crossing over between the X and Y
T/F

True

21

How can XY individuals can be phenotypically female?

Suppose one of the genes that determines “maleness” on the Y chromosome is defective

22

What is Androgen Insensitivity Syndrome?

Known as Intersex
A person is a female but has an XY chromosome
As a result, estrogen (chemical messenger confers a female phenotype) is not converted into testosterone (confers a male phenotype)
Then by default, a person who is genetically a male will develop phenotypically into a female
Occurs in 1 of 13,000 - 65,000 Births

23

How can a person can have an odd number of chromosomes (47)?

Because an egg may have two of a certain chromosome in the egg then it is fertilized which means there is a third chromosome.
Normally only Trisomy 21 (Down's syndrome) is the only case that will not result in the death of the baby before birth

24

What is Klinefelter's syndrome?

Additional X chromosome
XXY so they have 47 chromosomes
They are men who have some female qualities
Can be treated by receiving injections of male testosterone