Meiosis
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Meiosis The reason everyone wears different shoes
A few definitions… • Heredity – Is the transmission of traits from one generation to the next
• Variation – Shows that offspring differ somewhat in appearance from parents and siblings
• Genetics – Is the scientific study of heredity and variation
Traits: From Parent to Offspring • Offspring acquire genes from parents by inheriting chromosomes • Genes – Are segments of DNA – Are located on the chromosomes – Are the units of heredity 16.1
Asexual Reproduction • One parent produces genetically identical offspring by mitosis • Example – bacteria dividing
16.2
Sexual Reproduction • Two parents give rise to offspring that have genes inherited from the two parents
16.2
Differing Sexual Life Cycles
16.4
A Karyotype – Is a microscopic representation of the chromosomes in a cell
Diploid vs. Haploid • A diploid cell (somatic cells) – Has two sets of each chromosome • n=number of chromosomes • Diploid cells are 2n (2 x n)
• A haploid cell (sperm and egg cells in humans) – Has one of each chromosome • Haploid cells are n 16.3
Meiosis • reduces the number of chromosome sets from diploid to Diploid haploid
Haploid
16.5/6
Meiosis I
16.5/6
Meiosis II
Three Differences • Synapsis and crossing over
• Tetrads on the metaphase plate
• Separation of homologues
In species that reproduce sexually – The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises each generation
In independent assortment –
Each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs Key Maternal set of chromosomes Paternal set of chromosomes
Possibility 1
Possibility 2
Two equally probable arrangements of chromosomes at metaphase I
Metaphase II
16.8
Daughter cells Combination 1
Combination 2
Combination 3
Combination 4
Synapsis and crossing over – Homologous chromosomes physically connect and exchange genetic information
16.7/8
Huge variability… Independent assortment, crossing over and random fertilization (any sperm joining with any egg) is thought to result in 64 trillion diploid combinations
16.8
A few definitions… • Heredity – Is the transmission of traits from one generation to the next
• Variation – Shows that offspring differ somewhat in appearance from parents and siblings
• Genetics – Is the scientific study of heredity and variation
Traits: From Parent to Offspring • Offspring acquire genes from parents by inheriting chromosomes • Genes – Are segments of DNA – Are located on the chromosomes – Are the units of heredity 16.1
Asexual Reproduction • One parent produces genetically identical offspring by mitosis • Example – bacteria dividing
16.2
Sexual Reproduction • Two parents give rise to offspring that have genes inherited from the two parents
16.2
Differing Sexual Life Cycles
16.4
A Karyotype – Is a microscopic representation of the chromosomes in a cell
Diploid vs. Haploid • A diploid cell (somatic cells) – Has two sets of each chromosome • n=number of chromosomes • Diploid cells are 2n (2 x n)
• A haploid cell (sperm and egg cells in humans) – Has one of each chromosome • Haploid cells are n 16.3
Meiosis • reduces the number of chromosome sets from diploid to Diploid haploid
Haploid
16.5/6
Meiosis I
16.5/6
Meiosis II
Three Differences • Synapsis and crossing over
• Tetrads on the metaphase plate
• Separation of homologues
In species that reproduce sexually – The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises each generation
In independent assortment –
Each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs Key Maternal set of chromosomes Paternal set of chromosomes
Possibility 1
Possibility 2
Two equally probable arrangements of chromosomes at metaphase I
Metaphase II
16.8
Daughter cells Combination 1
Combination 2
Combination 3
Combination 4
Synapsis and crossing over – Homologous chromosomes physically connect and exchange genetic information
16.7/8
Huge variability… Independent assortment, crossing over and random fertilization (any sperm joining with any egg) is thought to result in 64 trillion diploid combinations
16.8
