Biology H - Meiosis

Heredity

The transmission of traits from one generation to the next

Genetics

The study of heredity

Species

A group of organisms that have similar characteristics and can mate to produce viable (can survive), fertile (can reproduce) offspring

Children do not inherit physical traits themselves. They actually inherit…

Genes

Genes (and where they are)

Segments of DNA used as the unit of heredity; each gene has a specific locus (location) on a specific chromosome

Gametes

Reproductive cells

Gametes are (2N/N)…

Haploid (N)

Fertilization

The process that restores (doubles) gametes’ chromosome # after gonads produce them

During fertilization, N gametes become…

2N

Asexual reproduction is characterized by:

- Only needing 1 parent

- Producing identical offspring

Sexual reproduction is characterized by:

- Needing 2 parents

- Producing unique offspring

List the 5 types of asexual reproduction:

- Budding

- Vegetative propagation

- Binary fission

- Regeneration

- Sprouting

Budding (give example)

- Type of asexual reproduction

- A cell divides nuclear and cytoplasmic material unequally to produce a new cell

- Happens among both unicellular and multicellular organisms

- Seen in Hydra, where they develop a bud on its body wall that becomes another one

Vegetative propagation

- Type of asexual reproduction

- Formation of a genetically identical plant through a leaf, stem or root

- Seen in Spider plants, where sprouts called “pups” grow at the ends of long, slender stems

Binary fission

- Type of asexual reproduction

- Exclusive to prokaryotes due to their single circular chromosome

- A (prokaryotic) cell divides both nuclear and cytoplasmic material equally to produce a new cell

Regeneration

- Type of asexual reproduction

- The restoration of a body part or an entire organism (through mitosis)

- Seen in earthworms, lizards and starfish

Sporulation

- Type of asexual reproduction

- Formation of spores (name for cells produced in sporulation) through mitosis, which then disperse into the environment and create more of that same organism

- Seen in mushrooms

All human somatic (body) cells are…

Diploid (2N)

Chromosome pair 23 in males is…

Non-homologous (XY/Xx)

Although the 23rd chromosome pair in males is sometimes called XY, the 2nd chromosome, it’s just … when compared to the 1st chromosome

differently sized and shaped

Chromosome pair 23 in females is…

Homologous (XX)

Karyotype

Picture of chromosome pairs

Homologous chromosome pairs

A pair of chromosomes that are similar in size, shape and the traits (characteristics) they code for

Homologous pairs are NOT…

Identical

Autosomes

- Non-sex chromosomes

- Humans have 22 pairs

- Homologous in both males and females

Write down the condition this person has (if they do), and their karyotype notation:

- Turners syndrome

- (45, X0)

Write down the condition this person has (if they do), and their karyotype notation:

- Down syndrome

- (47, XY, + 21)

Write down the condition this person has (if they do), and their karyotype notation:

- Klinefelters syndrome

- (47, XXY)

Replication (when it happens, what it does)

- Single chromatid makes identical copy to form system chromatid

- Occurs prior to cell division (S phase)

- The moment when single-stranded chromosome become double-stranded

Human gametes have … chromosome(s)

23

A gamete has … autosome pairs and … sex chromosome(s)

22; 1 (either X or Y)

Eggs and sperm are…

Gametes

- An egg can only be a X chromosome, but sperm can either be X or Y chromosomes

This explains two things:

- Why male determines the sex of the offspring

- Why all humans have an X chromosome on the 23rd pair

Gonads (and 2 examples)

- Diploid (2N) sex glands that produce haploid (N) gametes through meiosis

- Include testes and ovaries

Zygote (2N or N?)

- Fertilized egg cell

- Diploid (2N)

Meiosis can be broken down into…

- Meiosis I (reduction)

- Meiosis II (division)

Meiosis affects the chromosome number of a cell by a factor of…

1/2

In Meiosis, cells go from … to…

Diploid (2N)→Haploid (N)→Haploid (N)

3 defining features in Meiosis I (reduction)

- Homologous chromosomes separate

- Two haploid (N) daughter cells form

- Chromosomes remain double-stranded

3 defining features in Meiosis II (division)

- Sister chromatids separate

- Four haploid (N) daughter cells form

- Chromosomes become single-stranded

Interphase happens prior to…

Mitosis/Meiosis

Prophase 1 (P1)

- Cell is 2N

- Chromosomes condense

- Sinapsis occurs

- Crossing over occurs

- Tetrads are formed

Crossing over

- Happens in P1

- Homologues exchange a segment of genetic material

- Increases variation by combining the DNA of 2 parents into 1 chromosome

Sinapsis

- Pairing of homologues

- Never happens during mitosis

Tetrads

- A group or set of four formed by paired homologous chromosomes (four chromatids) in P1

- Each has at least one chiasmata

Chiasmata

X-shaped region where crossing over occured

Metaphase 1 (M1)

- Cell is 2N
- Tretrads line up in pairs at the metaphase plate, one facing each pole

- Microtubules are attached to the centromeres of each tetrad

Anaphase 1 (A1)

- Cell is 4N

- Pairs of homologous chromosomes separate

- Separated chromosomes move towards each pole-guided by apparatus

Telophase 1 (T1)

- Each half of the cell is N

- All chromosomes still consist of two sister chromatids individually

- Cleavage furrow (for animals) or cell plate (for plants) is seen

Chromosomes (do/do not) replicate in between reduction (Meiosis I) and division (Meiosis II)

do not

Prophase 2 (P2)

- Cells are N

- Very similar to mitosis; a spindle apparatus forms

- The two sister chromatids of each chromosome are no longer identical (due to crossing over in Meiosis I)

Metaphase 2 (M2)

- Cells are N

- Double-stranded chromosomes are arranged at the equator

- The centromeres of sister chromatids attach to microtubules extending from opposite poles

Anaphase 2 (A2)

- Cells are N

- Sister chromatids separate; they now move as two newly individual chromosomes toward opposite poles

Telophase 2 (T2)

- Cells are N

- Chromosomes arrive at opposite poles

- Nuclei (for the 4 individual cells) are formed

- Chromosomes decondense into chromatin

The original source of any variation is a…

Mutation

Sexual reproduction is advantageous because…

It contributes to variation, which enhances a species’ success in survival when environmental changes occur

Independent assortment

Random combinations formed during mitosis

Humans can form … independent assortments

Over 8 million

Random fertilization

Any sperm can fertilize any egg