Meiosis and Sexual Life Cycles

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Variations on a Theme

Living organisms are distinguished by their ability to reproduce their own kind

Genetics is the scientific study of heredity and variation

Heredity is the transmission of traits from one generation to the next

Variation is demonstrated by the differences in appearance that offspring show from parents and siblings

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Fig. 13-1

Slide 3

Concept 13.1: Offspring acquire genes from parents by inheriting chromosomes

In a literal sense, children do not inherit particular physical traits from their parents

It is genes that are actually inherited

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Inheritance of Genes

Genes are the units of heredity, and are made up of segments of DNA

Genes are passed to the next generation through reproductive cells called gametes (sperm and eggs)

Each gene has a specific location called a locus on a certain chromosome

Most DNA is packaged into chromosomes

One set of chromosomes is inherited from each parent

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Comparison of Asexual and Sexual Reproduction

In asexual reproduction, one parent produces genetically identical offspring by mitosis

A clone is a group of genetically identical individuals from the same parent

In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents

Video: Hydra Budding

Slide 6

Fig. 13-2

(a) Hydra

(b) Redwoods

Parent

Bud

0.5 mm

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Fig. 13-2a

(a) Hydra

0.5 mm

Bud

Parent

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Fig. 13-2b

(b) Redwoods

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Concept 13.2: Fertilization and meiosis alternate in sexual life cycles

A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism

Slide 10

Sets of Chromosomes in Human Cells

Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes

A karyotype is an ordered display of the pairs of chromosomes from a cell

The two chromosomes in each pair are called homologous chromosomes, or homologs