Chapter 10: Sexual Chapter 10: Sexual Reproduction and Reproduction and

GeneticsGenetics

10.1 - Meiosis10.1 - Meiosis

Chromosomes and Chromosomes and Chromosome NumberChromosome Number

• TraitTrait – Characteristics (hair color, – Characteristics (hair color, height, or eye color)height, or eye color)

• GenesGenes – DNA segment that control – DNA segment that control the production of a protein.the production of a protein.

Homologous Homologous chromosomeschromosomes

Homologous Homologous ChromosomesChromosomes

• Humans have 46 chromosomes.Humans have 46 chromosomes.• Each parent contributes 23 Each parent contributes 23

chromosomes, resulting in 23 pairs chromosomes, resulting in 23 pairs of chromosomes.of chromosomes.

• Homologous ChromosomesHomologous Chromosomes – – Chromosomes that make up a pair. Chromosomes that make up a pair. One chromosome from each parent.One chromosome from each parent.

Haploid and Diploid CellsHaploid and Diploid Cells

• Haploid CellHaploid Cell – A cell – A cell with with nn number of number of chromosomes.chromosomes.

• FertilizationFertilization – The – The process by which process by which one haploid gamete one haploid gamete combines with combines with another haploid another haploid gamete.gamete.

• Diploid CellDiploid Cell – A cell – A cell with with 2n2n number of number of chromosomes.chromosomes.

Meiosis IMeiosis I

Meiosis IMeiosis I

• MeiosisMeiosis – A type of cell division that – A type of cell division that reduces the number of reduces the number of chromosomes. (reduction division)chromosomes. (reduction division)

Meiosis IMeiosis I

• InterphaseInterphase::• Chromosomes replicateChromosomes replicate• Chromatin condensesChromatin condenses

Meiosis IMeiosis I

• Prophase IProphase I::• Pairing of homologous chromosomes Pairing of homologous chromosomes

occurs, each chromosome consists of occurs, each chromosome consists of two chromatids.two chromatids.

• Crossing overCrossing over produces exchange of produces exchange of genetic information. The nuclear genetic information. The nuclear envelope breaks down. (Figure 10.4)envelope breaks down. (Figure 10.4)

• Spindles form.Spindles form.

Prophase IProphase I

Meiosis IMeiosis I

• Metaphase IMetaphase I::• Chromsome centromeres attach to Chromsome centromeres attach to

spindle fibers.spindle fibers.• Homologous chromosomes line up at Homologous chromosomes line up at

the equator.the equator.

Metaphase IMetaphase I

Meiosis IMeiosis I

• Anaphase IAnaphase I::• Homologous chromosomes separate Homologous chromosomes separate

and move to opposite poles of the and move to opposite poles of the cell.cell.

Anaphase IAnaphase I

Meiosis IMeiosis I

• Telophase ITelophase I::• The spindles break down.The spindles break down.• Chromosomes uncoil and form two Chromosomes uncoil and form two

nuclei.nuclei.• The cell divides.The cell divides.

Telophase ITelophase I

Meiosis IIMeiosis II

• Meiosis in only halfway completed at Meiosis in only halfway completed at the end of meiosis I.the end of meiosis I.

Prophase IIProphase II

• Chromosomes condense.Chromosomes condense.• Spindles from in each new cell.Spindles from in each new cell.• Spindle fibers attach to Spindle fibers attach to

chromosomes.chromosomes.

Metaphase IIMetaphase II

• Centromeres of chromosomes line Centromeres of chromosomes line up randomly at the equator of each up randomly at the equator of each cell.cell.

Anaphase IIAnaphase II

• Centromeres split.Centromeres split.• Sister chromatids separate and Sister chromatids separate and

move to opposite poles.move to opposite poles.

Telophase IITelophase II

• Four nuclei form around Four nuclei form around chromosomes.chromosomes.

• Spindles break down.Spindles break down.• Cells divide.Cells divide.

Product!Product!

• Four cells have formed.Four cells have formed.• Each nucleus contains a haploid Each nucleus contains a haploid

number of chromosomes.number of chromosomes.

10.2 Mendelian Genetics10.2 Mendelian Genetics

• GeneticsGenetics – The – The science of science of heredity.heredity.

• MendelMendel – Father of – Father of geneticsgenetics

The Inheritance of TraitsThe Inheritance of Traits

• Cross green-seed plant with a yellow-Cross green-seed plant with a yellow-seed plant – Parent (P) generationseed plant – Parent (P) generation

• FF11and Fand F22 generations generations

• First Filial (FFirst Filial (F11) generation – All yellow) generation – All yellow

• Self fertilizationSelf fertilization

• Second Filial (FSecond Filial (F22) generation – 6022 ) generation – 6022 yellow and 2001 green (a 3:1 ratio)yellow and 2001 green (a 3:1 ratio)

Genes in PairsGenes in Pairs

• AlleleAllele – Alternative form of a single – Alternative form of a single gene passed from generation to gene passed from generation to generation.generation.

• Dominant and recessive (3:1)Dominant and recessive (3:1)

DominanceDominance

• Dominant gene – YDominant gene – Y• Recessive gene – yRecessive gene – y• Homozygous Homozygous – An organism with two – An organism with two

of the same alleles for a particular of the same alleles for a particular trait.trait.

• HeterozygousHeterozygous – An organism with – An organism with two different alleles for a particular two different alleles for a particular trait. (Yy)trait. (Yy)

Genotype and PhenotypeGenotype and Phenotype

• GenotypeGenotype – The organism’s allele – The organism’s allele pairs.pairs.

• PhenotypePhenotype – The observable – The observable characteristic or outward expression characteristic or outward expression of an allele pair.of an allele pair.

Mendel’s Law of Mendel’s Law of SegregationSegregation

• States that the two alleles for each States that the two alleles for each trait separate during meiosis.trait separate during meiosis.

• HybridsHybrids – Genotype Yy and has – Genotype Yy and has yellow seeds.yellow seeds.

Monohybrid CrossMonohybrid Cross

• A cross that involves hybrids for a A cross that involves hybrids for a single trait.single trait.

• Genotypic ratio is 1:2:1Genotypic ratio is 1:2:1• Phenotypic ratio is 3:1Phenotypic ratio is 3:1

Dihybrid CrossDihybrid Cross

• Heterozygous for two traits.Heterozygous for two traits.

Law of Independent Law of Independent AssortmentAssortment

• States that a random distribution of States that a random distribution of alleles occurs during gamete alleles occurs during gamete formation.formation.

Punnett SquaresPunnett Squares

• Developed by Dr. Developed by Dr. Punnett in the Punnett in the early 1900s to early 1900s to predict possible predict possible offspring between offspring between two known two known genotypes.genotypes.

Monohybrid CrossMonohybrid Cross

Dihybrid Cross (F2 Dihybrid Cross (F2 Generation)Generation)

10.3 – Gene Linkage and 10.3 – Gene Linkage and PolyploidyPolyploidy

• Genetic RecombinationGenetic Recombination – The new – The new combination of genes produced by combination of genes produced by crossing over and independent crossing over and independent assortment.assortment.

• Genetic Recombination formula is 2Genetic Recombination formula is 2nn

Gene LinkageGene Linkage

• Genes that are located close to each Genes that are located close to each other on the same chromosome are other on the same chromosome are linked and usually travel together linked and usually travel together during gamete formation. (Figure during gamete formation. (Figure 10.14)10.14)

• Makes an exception to Mendel’s law Makes an exception to Mendel’s law of independent assortment.of independent assortment.

PolyploidyPolyploidy

• PolyploidyPolyploidy – The occurrence of one – The occurrence of one or more extra sets of all or more extra sets of all chromosomes in an organism.chromosomes in an organism.

• Polyploidy formula is 3Polyploidy formula is 3nn or greater. or greater.• Lethal in humansLethal in humans