Chapter 13: Meiosis and Sexual Life Cycles

Study of heredity and variation.

genetics

Transmission of traits from one generation to the next.

heredity

Differences in appearance that offspring show from parents and siblings.

variation

Unit of heredity; made up of DNA segments that code for specific traits.

gene

Specific location of a gene on a chromosome.

locus

Genes are passed to the next generation through

gametes

Long DNA molecules packaged with proteins; most DNA is stored here.

chromosomes

Ordered display of all chromosomes in a cell.

karyotype

Pair of chromosomes (one from each parent) with the same genes, size, and shape

homologous chromosomes

The 22 pairs of non-sex chromosomes.

autosomes

how many pairs of autosomes are there

22

Determine biological sex.

sex chromosomes

XX

females

XY

male

All body cells except gametes

somatic cells

Sperm and egg cells

gametes

Diploid (2n) — two sets

somatic cells

Haploid (n) — one set

gametes

Fertilized egg (fusion of sperm + egg)

zygote

is a zygote haploid or diploid

diploid

46 chromosomes

diploid

23 chromosomes

haploid

Single individual passes all genes to offspring.

asexual reproduction

is there a fusion of gametes in asexual reproduction

no

Offspring are clones — genetically identical.

asexual reproduction

Two parents contribute genes → offspring with unique genetic combinations.

sexual reproduction

offspring with unique genetic combinations.

sexual reproduction

Involves meiosis and fertilization

sexual reproduction

animal life cycle

Gametes → fertilization → zygote → mitosis → multicellular diploid.

fungi life cycle

Zygote immediately undergoes meiosis to form haploid cells → grow by mitosis → produce gametes.

Diploid generation → meiosis → produces spores

sporophyte

Haploid generation → mitosis → produces gametes.

gametophyte

Growth, repair, asexual reproduction

mitosis

purpose is Sexual reproduction

meiosis

how many divisions are in mitosis

1

how many divisions are in meiosis

2

how many daughter cells are made in mitosis

2

how many daughter cells are made in meiosis

4

chromosome number is same as parent (2n → 2n)

mitosis

chromosome number is Half of parent (2n → n)

meiosis

Crossing over, independent assortment, homolog separation

meiosis

Reduce chromosome number from diploid (2n) to haploid (n) and increase genetic diversity

meiosis

Reductional Division

meiosis i

Equational Division

meiosis II

homologous chromosomes separate

meiosis I

sister chromatids separate

meiosis II

Chromosomes condense, nuclear envelope breaks down

prophase I

Homologous chromosomes pair up, forming tetrads

synapsis

what does synapsis form

tetrads

Non-sister chromatids exchange DNA segments at points called chiasmata → increases genetic variation.

crossing over

where do sister chromatids exchange DNA segments in crossing over

chiasmata

when does the spindle form

prophase

when does crossing over happen

prophase I

Homologous pairs line up at metaphase plate.

metaphase I

Random orientation =

independent assortment

Homologous chromosomes separate and move to opposite poles.

anaphase I

Sister chromatids remain attached

anaphase I

Two haploid daughter cells form.

telophase I

Period between meiosis I and II.

interkinesis

Centrioles may duplicate.

interkinesis

Spindle forms; nuclear envelope breaks down again.

prophase II

Chromosomes line up at the metaphase plate.

metaphase II

Sister chromatids separate and move to opposite poles.

anaphase II

Change in DNA sequence; source of new alleles.

mutation

Exchange of DNA between homologous chromosomes.

crossing over

Produces recombinant chromosomes with DNA from both parents.

crossing over

what does crossing over produce

recombinant chromosomes

Random orientation of homologous pairs → random combination of maternal and paternal chromosomes.

independent assortment

what are the 4 sources of genetic variaiton

1. mutation

2. crossing over

3. independent assortment

4. random fertilization

Study of heredity and variation

genetics

Transmission of traits from one generation to the next

heredity

Differences among individuals

variation

Unit of heredity; segment of DNA

gene

Gene's location on a chromosome

locus

DNA molecule with genetic information

chromosome

Ordered display of chromosomes

karyotype

Same genes, length, and centromere position

homologous chromosomes

Non-sex chromosomes (pairs 1-22 in humans)

autosomes

X and Y chromosomes that determine sex

sex chromosome

Two sets of chromosomes (body cells)

diploid

One set of chromosomes (gametes)

haploid

Fertilized egg; diploid

zygote

One parent; identical offspring

asexual reproduction

Two parents; genetic variation

sexual reproduction

Genetically identical individual

clone

Division to produce haploid gametes

meiosis

Exchange of DNA between homologous chromosomes

crossing over

Random distribution of chromosomes

independent assortment

Any sperm fertilizing any egg

random fertilization

Pairing of homologous chromosomes in Prophase I

synapsis

Group of four chromatids formed during synapsis

tetrad

Site of crossing over

chiasmata

scientific study of heredity and variation

genetics

transmission of traits from one generation to the next

heredity

differences in appearance or traits among individuals in a population

variation

segment of DNA that codes for a specific trait

gene

specific location of a gene on a chromosome

locus

one parent produces genetically identical offspring without gamete fusion

asexual reproduction

two parents produce genetically identical offspring through fusion of gametes

sexual reproduction

genetically identical individuals from same parent

clone