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T2 Biology > Meiosis and Gametogenisis > Flashcards

Meiosis and Gametogenisis Flashcards

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0
Q

What is Meiosis?

A

Meiosis is the process by which gametes are produced(gametogenesis)

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1
Q

What are homologous chromosomes

A

Chromosome pairs, similar in structure, that contain the Sam sequence of genes. One copy is paternal and the other is maternal; they come from two parents

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2
Q

What is Oogenesis?

A

The formation of eggs

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3
Q

What is spermatogenesis?

A

The formation of sperm

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4
Q

What are gametes

A

Egg and sperm

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5
Q

What are diploid and haploid cells?

A

Cells of the body are diploid cells: they have two sets of each chromosome (2n) Egg & Sperm have a haploid nucleus: one set of each chromosome (1n)

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6
Q

Function of Meiosis

A

Meiosis reduces the diploid number of chromosomes (in humans 46) to the haploid number of chromosomes(23)

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7
Q

Why is Meiosis called a reduction division?

A

Because a diploid parental cell (immature egg or sperm) divided into four haploid cells (2n>>1n)

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8
Q

How does meiosis work?

A

One replication of chromosomes Two cell divisions(meiosis I and meiosis II)

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9
Q

What are features of meiosis

A

Crossing over Independent assortment

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10
Q

What happens during interphase?

A

Interphase: before meiosis begins The chromosomes replicate to produce two copies of each homologous chromosome. The two copies are called sister chromatids, attached to each other by a centromere

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11
Q

What happens during Meiosis I: early Prophase I?

A
  1. Chromosomes condense; become visible 2. Nuclear membrane disappears 3. Centrosomes duplicate; move to opposite poles of cell 4. Spindle fibers start to form
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12
Q

What happens during late prophase I?

A
  1. Homologous chromosomes pair up together 2. They are in continuous contact in their lengths 3, while they are in contact they exchange segments of chromosomes (Crossing over)
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13
Q

Describe the process of crossing over

A

DNA on non-sister chromatids break at corresponding points among their length; DNA on on sister chromatids reattaches; As a result, genes are swapped between non-sister chromatids. (During crossing over, broken ends rejoins at corresponding sites)

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14
Q

What is Chiasma

A

The point where two different chromatids on homologous chromosomes break and exchange a piece is shaped like a cross

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15
Q

Synonym of crossing over

A

Recombination: the re-assortment of genes into new combinations

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16
Q

What does crossing over do

A

It increases the genetic variation by the recombination of genes; It can occur in random places along the chromosome at several different positions, thus it can produce an infinite amount of combinations of genes

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17
Q

What happens during Metaphase I

A

The homologous pairs line, side by side, at the equator; Spindle fibers attach to centromeres

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18
Q

What is independent assortment

A

Random orientation of the homologous pairs can occur; each pair may orient with its maternal or paternal homolog closer to a given pole; Thus, which chromosome goes to which pole is completely random

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19
Q

What does independent assortment lead to

A

It leads to genetic variation, as genes on different chromosomes are re-assorted

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20
Q

Why are cells generated by meiosis genetically different from each other

A

Crossing over and independent assortment

21
Q

What happens during Anaphase I

A

Spindle fibers shorten, Homologous pairs are separated and pulled to opposite poles; Sister chromatids remain attached to the centromeres

22
Q

What type of a division is Anaphase I

A

A reduction division

23
Q

What happens during Telophase I?

A

Nuclear membrane form and cytoplasm begins cytokinesis Spindle fibers break Nucleus is no longer diploid; each nucleus contains one pair of sister geomatics for each chromosome (haploid set) If crossing over has occurred, sister chromatids are no longer identical

24
Q

What happens during Prophase II(meiosis II)?

A

The sister chromatids are attached by their centromeres; The nuclear membrane breaks down again, chromosomes shorten and condense;’centrioles move to the opposite pile of the cell; Spindle fibers start forming

25
Q

What happens during Metaphase II?

A

Each chromosome, consisting of one pair of sister chromatids, line up at the equator attached by their centromere;each chromosome is attached to now the fully formed spindle

26
Q

What happens during Anaphase I?

A

The centromeres separate, and the two chromatids move to opposite poles on the spindle The separated chromatids are now called chromosomes

27
Q

What happens during Telophase II& cytokinesis

A

A nuclear envelope forms around each set of chromosomes: 4 nuclei are formed; chromosomes uncoil Cytokinins takes place, producing four daughter cells each with a haploid set of chromosomes Because of crossing over, some chromosomes have recombined segments of the original parental chromosomes

28
Q

Properties of spermatogenesis

A

-begins at puberty -occurs in the testes The products of spermatogenesis are four haploid cells (Sperm); cytoplasm is equally divide amount four sperm. Each Sperm is 1/4 of the original diploid cell

29
Q

Properties of Oogenesis

A

Occurs in ovary In the human female, the first part of meiosis begins in the embryo. Until puberty, oocytes are in prophase I; After that groups of oocytes periodically resume meiosis

30
Q

Process of Oogenesis

A

The products of Oogenesis are one haploid egg And three polar bodies Egg is the same size of original diploid cell Polar bodies are not used and degenerate

31
Q

Why is the shape of the chromosome characteristic?

A

Size of the arms depends on the position of the centromere

32
Q

What is karyotyping?

A

the examination of the chromosomes number structure

33
Q

How do you obtain a karyotype?

A

Chromosomes are isolated, stained, and examined under the microscope. A picture of the chromosomes is taken through the microscope. The picture of the chromosomes is cut up and chromosomes are arranged as homologous pairs in descending order of size.

34
Q

How are chromosomes organized?

A

Based on their size in pairs of 23

35
Q

On what tissues can karyotyping be performed?

A

Amniotic fluid, Placenta, Blood and Bone Marrow

36
Q

What does amniocentesis allow

A

prenatal diagnosis of chromosome abnormalities gender determination

37
Q

What is non-disjunction

A

If meiosis does not occur properly in one of the parents, the resulting gamete has an abnormal number of chromosomes; this error in meiosis is called nondisjunction

38
Q

What is the result of non-disjunction

A

Formation of gametes with too many or too little chromosomes, baby is born with genetic diesease

39
Q

What are defective gametes

A

aneuploid

40
Q

What types of chromosome abnormalities does nondisjunction lead to

A

Trisomy and Monosomy

41
Q

What is trisomy

A

a third chromosome of one type is present

42
Q

What is monosomy

A

one chromosome is missing.Monosomies are usually lethal during early fetal development. Only known survivably monosomy is Turner Syndrome

43
Q

What happens when there is a nondisjunction of chromosome 21 during egg formation

A

Down syndrome (trisomy 21), individual has 3 copies of chromosome 21 (47 chromosomes) Mental retardation and distinct physical traits; Probability increases with age of the mother Under 20 years: risk about 1:1700 20-30 years: risk about 1:1400 30-35 years: risk about 1:750 45 years: risk about 1:16

44
Q

Example of human abnormalities due to the non-disjunction of sex chromosomes

A

For example: in the mother X chromosomes do not separate during meiosis II; Resulting eggs will be : XX and O

45
Q

If the XX gamete combines during non-disjunction with an X gamete…

A

with an X gamete, the resulting zygote is a female XXX, usually sterile (XXX Syndrome);

46
Q

If the XX gamete combines during non-disjunction with a Y gamete…

A

with a Y gamete, the resulting zygote is XXY, sterile male with enhanced female characteristics (breast) and diminished mental capacities (Klinefelter syndrome

47
Q

If a O gamete combines (X gamete)…

A

with an X gamete, the resulting zygote is XO, sterile female, does not mature sexually (Turner syndrome)

48
Q

If a O gamete combines (y gamete)..

A

with a Y gamete, the resulting zygote is nonviable;

49
Q

Cause of human abnormalities

A

alterations in sex chromosome number

50
Q

What happens when an XY chromosome joins with an Y gamete

A

the resulting zygote is XYY, fertile male, with learning difficulties and violent tendencies

T2 Biology (7 decks)

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