Introduction to Genetics Chapter 6 Mr. Scott

Meiosis Meiosis Meiosis Chromosome number Fruit fly Body cell – 8 Chromosomes 4 from mom 4 from dad Homologous chromosomes – Matching to each other

Meiosis Autosomes – Chromosomal pairs Autosomes – Chromosomal pairs Found in Somatic cells Found in Somatic cells Sex Chromosomes – 23 rd pair Sex Chromosomes – 23 rd pair Gametes Gametes X or Y X or Y

Meiosis Sexual Reproduction – uniting of gametes in reproducing organisms Sexual Reproduction – uniting of gametes in reproducing organisms Fertilization – Nuclei fuse to form one nucleus Fertilization – Nuclei fuse to form one nucleus What has to happen to the parent cells for this to occur? What has to happen to the parent cells for this to occur?

Meiosis Diploid – cell that has both sets of homologous chromosomes 2N Body cells Haploid – cells that have just one set of chromosomes 1 N Sex cells

Meiosis Phases of meiosis A process of reduction and division in which the number or chromosomes per cell is cut in half through the separation of homologous chromosome in a diploid cell

Meiosis Meiosis I Prophase I Each chromosome lines up with its corresponding homologous chromosome making a tetrad They exchange genetic information called crossing-over Homologous chromosomes separate and form two new cells with different chromosome and alleles

Meiosis Meiosis II Two new cells divide Neither cell makes a copy of the chromosomes All four new cells have one set of chromosomes

Meiosis Gamete formation Haploid cells Sperm or pollen Eggs

Meiosis Mitosis vs. Meiosis Mitosis vs. Meiosis Mitosis results in two genetically identical diploid cells Meiosis results in four genetically different haploid cells

The Work of Gregor Mendel The work of Gregor Mendel The work of Gregor Mendel Austrian monk who is the father of Genetics Genetics – the scientific study of heredity

The Work of Gregor Mendel Fertilization – when male and female reproductive cells join Male – pollen or sperm Female – eggs Gamete – the individual egg or sperm Seed – fertilized egg or new cell (zygote)

The Work of Gregor Mendel True-breeding – if they were allowed to self-breed they would have identical offspring Self-breeding – Sperm and egg from the same flower fertilize Experiment Cross-pollination Mendel took sperm from one plant and fertilized eggs from other plants

The Work of Gregor Mendel Genes and Dominance Traits – a specific characteristic (ex. Brown hair) Seed color Plant height Parental generation (P) – Original pair of plants Filial generation (F 1 ) – offspring, progeny Hybrids – offspring of crosses between parents with different traits

The Work of Gregor Mendel Genes – chemical factors that determine traits (Hair color) Alleles – different forms of traits (Brown hair, blue eyes)

The Work of Gregor Mendel Principle of Dominance – some alleles are dominant and other are recessive Dominant traits will always show over recessive traits

The Work of Gregor Mendel Segregation F 1 generation self-pollinated F 1 X F 1 = F 2 F 1 Cross ¼ of the F 2 plants now show the recessive traits

The Work of Gregor Mendel Explaining the F 1 Cross When each F1 plant flowers and produces gametes, the two alleles segregate from each other so that each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness. Segregation -separation of alleles during gamete formation

Probability and Punnett Square Probability and Punnett Square Probability and Punnett Square Probability in Genetics Probability – the likelihood that a particular event will occur Coin flip ½ or 50 % 3 Coin flips ½ X ½ X ½ = 1/8 Past outcomes do not affect future ones

Probability and Punnett Square Punnett Square A diagram showing the gene combinations that might result from a genetic cross Letters represent each allele Top and left letters are the parents genes The four boxes show each possible gene combination

Probability and Punnett Square GG, Gg, gg are all of the possible combinations of genes GG means homozygous dominant gg means homozygous recessive Gg means heterozygous

Probability and Punnett Square Phenotype Physical characteristics Tall or short Purple or white Genotype Genetic makeup GG, Gg, or gg

Probability and Punnett Square Probability and segregation Each parent only donates one of their two alleles to each offspring

Probability and Punnett Square Probabilities predict averages, not exact outcomes Probability is more accurate when you have more chances

Exploring Mendelian Genetics Two-factor cross : F1 Crossing true-breeding organisms does not answer this question They do produce hybrid offspring used for the next test RrYy

Exploring Mendelian Genetics Two-factor cross : F 2 9:3:3:1 ratio

Exploring Mendelian Genetics Exploring Mendelian Genetics Exploring Mendelian Genetics Independent assortment The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

Exploring Mendelian Genetics Mendel’s Principles Mendel’s Principles The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These genes are segregated from each other when gametes are formed. In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These genes are segregated from each other when gametes are formed. The alleles for different genes usually segregate independently of one another. The alleles for different genes usually segregate independently of one another.

Exploring Mendelian Genetics Beyond dominant and recessive alleles Incomplete dominance – alleles are not completely dominant

Exploring Mendelian Genetics Codominance – both alleles contribute to the phenotype

Exploring Mendelian Genetics Multiple allele – more than two alleles Polygenic trait Two or more genes control one allele

Exploring Mendelian Genetics Mendel’s Principles Apply to animals as well as plants More importantly to humans

Exploring Mendelian Genetics Genetics and the Environment Environment affects how genes are displayed