Meiosis

secual reproduction produces offspring that contain

a unique combination of genes from the parents

secual reproduction depends on

the cellular processes of meiosis and fertilization

Different individuals of a single species have

the same number and types of chromosomes

A human somatic cell is

a typical body cell and has 46 chromosomes

To produce a karyotype, a technician can break open a human cell in

metaphase of mitosis,

To produce a karyotype, a technician can stain the

chromosomes with dyes

To produce a karyotype, a technician can take a picture with

the aid of a microscope, and arrange the chromosomes in matching pairs by size

Homologous chromosomes resemble each other in

length and centromere position

Homologous chromosomes carry

genes controlling the same inherited characteristics

Chromosome

A structure made of DNA and proteins that carries genetic information

Homologous Chromosomes is a matching pair of

chromosomes, one inherited from the mother and one from the father.

Homologous Chromosomes contain the same

genes in the same locations, but may have different alleles (versions of a gene).

Humans have

23 pairs of chromosomes (46 total).

Duplicated Chromosome Consists of

two identical sister chromatids joined together.

Sister Chromatids

Two identical copies of a chromosome after replication

Sister Chromatids is formed during

DNA replication

Sister Chromatids connected at

centromere

Centromere

The constricted region where sister chromatids are attached.

Centromere Helps ensure

chromosomes separate correctly during cell division.

Karyotype

A display of all chromosomes arranged in pairs according to size and shape.

Chromosomes 1-22 are called

autosomes

The 23rd pair are the

sec chromosomes

X chromosome is larger than

Y chromosome

Presence of XY indicates a

male karyotype

Before cell division, each chromosome replicates to form

two sister chromatids

Sister chromatids are held together by a

centromere

Homologous chromosomes have

same genes, shape, length but different version of genes (alleles)

Sister chromatids are identical copies of

one chromosome

Meiosis

the process of cell division that produces haploid gametes in diploid organisms,
resembles mitosis

first difference of meiosis between mitosis

number of chromosomes during meiosis is cut in half

2nd difference of meiosis between mitosis

exchange of genetic material—pieces of chromosomes between homologous
chromosomes

exchange of homologous chromosomes (crossing over) occurs

during the first prophase of meiosis

Meiosis is a type of cell division that produces

haploid gametes (sperm or egg cells)

meiosis reduces

chromosome number by half

divisions of meiosis

Meiosis I and Meiosis II.

Step 1 cell cycle with meiosis

Chromosomes Duplicate

Step 2 cell cycle with meiosis

Homologous Chromosomes Separate

Step 3 cell cycle with meiosis

Sister Chromatids Separate

Diploid (2n)

Contains two sets of chromosomes.

Haploid (n)

Contains one set of chromosomes

Independent Assortment

homologous chromosome pairs line up at the cell's equator, the orientation of each homologous pair is random

Each homologous chromosome pair acts independently of

every other pair

Metaphase I of meiosis

when homologous chromosome pairs align randomly before being separated in Anaphase I

result of independent assortment

Sperm and egg cells are genetically different from one another, gamete receives unique mix of chromosomes

Anaphase I

homologous chromosomes separate.

many chromosome combinations can be produced in

gametes

Possible chromosome combinations eq

2^n

ex Possible chromosome combinations eq

human (n = 23) there are 2^23, or about 8
million possible chromosome combinations

Crossing over

exchange of corresponding segments between nonsister chromatids of
homologous chromosomes

recombinant chromosomes

a chromosome that contains DNA from both the maternal and paternal homologous chromosomes - results due to crossing over

With crossing over, gametes arise with

recombinant chromosomes

recombinant chromosomes result from

genetic recombination

genetic recombination

production of gene combinations different from those carried by the parental chromosomes

Nonsister chromatids exchange

DNA

Sister chromatids do NOT exchange

DNA because they are identical copies

Crossing Over

Exchange of DNA segments

Independent Assortment

Random chromosome orientation

crossing Occurs in

Prophase I

Fertilization

Random sperm and egg unite

Fertilization occurs

After meiosis

Fertilization equation

sperm + egg → zygote (2n)

Zygote grows by

mitosis

Adults produce gametes through

meiosis

Gametes are

haploid (n)

Prophase I

crossing over occurs

Metaphase I

homologous chromosomes line up randomly (independent assortment)

Anaphase I

homologous chromosomes separate

Anaphase II

sister chromatids separate

where does homologous chromosomes come from

One chromosome from mom and one from dad.

Diploid Humans

46 chromosomes

Haploid Humans

23 chromosomes

In the equation number of possible gamete chromosome combinations 2^n, n is

haploid number

Meiosis produces

4 haploid cells

Mitosis produces

2 diploid cells

Life cycle of a person

Meiosis → Fertilization → Zygote → Adult

Gametes

sperm and egg

Zygote

fertilized egg

Meiosis Makes

gametes

Fertilization Forms

zygotes

Stages leading to and of meiosis

Interphase, Meiosis I, Meiosis II