CH 10 Mendel and Meiosis

What is Heredity? Heredity Genes The passing on of characteristics from parents to offspring through genes Genes A section on DNA that carries the information on what type of protein to make; they influence the types of traits an organism inherits

What is Heredity? Traits Characteristics that are inherited Genetics The branch of biology that studies heredity

History of Genetics Gregor Mendel: an Austrian monk that first studied genetics Experimented with pea plants to discover the general laws of genetics

History of Genetics A pea plant has gametes and both male and female reproductive organs Gametes: male and female sex cells

History of Genetics Pollination: transfer of pollen (male gametes) from a male reproductive organ to a female reproductive organ in a plant Mendel allowed pollination to occur within the same flower or between different flowers for his experiments Pollen grains Transfer pollen Female part Male parts Cross-pollination

History of Genetics Fertilization: the male gamete unites with the female gamete to form a zygote (a fertilized cell) In the case of pea plants, the zygote becomes a seed

Pea Plant Traits Tested By Mendel Recessive trait Dominant Seed shape color Flower position Pod Plant height round yellow purple axial (side) green inflated tall wrinkled white terminal (tips) constricted short

History of Genetics Conducted crosses between pea plants to compare traits Monohybrid cross: when only one trait is compared at a time (like eye color) Dihybrid cross: when two traits are compared at a time (like eye & hair color) P1 = Parental generation (parents) F1 = 1st filial generation (children) F2 = 2nd filial generation (grandchildren) Filial means “family”

Punnett Squares Used to compare traits Shorthand way of determining the probability of having a certain type of offspring if you know the parents’ genotypes

Section 10.1 Summary – pages 253-262 Punnett Square-Monohybrid cross Dad A Punnett square for this cross is two boxes tall and two boxes wide because each parent has two kinds of gametes for this trait, but will only pass one along to each offspring T t T TT Tt t Tt tt Mom Possible offspring Section 10.1 Summary – pages 253-262

Mendel’s Conclusion 1. The rule of unit factors Each organism has two factors, or genes, that control each trait One gene comes from mom, one gene comes from dad A single gene can exist in different forms called alleles Example: Blue, brown, and green are alleles for the eye color gene

FYI: Alleles Chromosomes = location of genes Gene = section of DNA on the chromosome that determines the type of protein (Ex. for color) produced Allele = different forms of a single gene (protein for a purple flower or a protein for a white flower)

Mendel’s Conclusion 2. The rule of dominance Offspring inherit an allele from each parent, but only one trait is observed Dominant trait: “stronger” trait that shows up when the dominant allele is present Represented by a capital letter; T is for tallness Recessive trait: “weaker” trait that shows up only when the dominant allele is not present Represented by a lowercase letter; t is for shortness

The Rule of Dominance T T t Tt Tt Results: All tall plants Tall plant Short plant t Tt Tt T T t t T t F1 All tall plants Results: All tall plants T t

Mendel’s Law of Segregation What is means: Every organism has 2 alleles of each gene When gametes are made, each gamete receives only one of these alleles During fertilization, the offspring will receive one allele for each gene from each parent

Mendel’s Law of Segregation Parents: Tt x Tt Results: 3 tall plants, 1 short plant T t T t TT Tt Tt tt

Phenotypes & Genotypes Phenotype: the physical appearance of an organism Ex. Blue skin Genotype: genetic makeup of an organism Ex. Alleles for skin color are B (=blue) or b (= black)

Homozygous vs. Heterozygous Homozygous: 2 alleles for a trait are the same BB is homozygous dominant for blue skin bb is homozygous recessive for black skin Homozygous offspring are called purebred because their alleles are the same

Homozygous vs. Heterozygous Heterozygous: 2 alleles for a trait are not the same Bb is heterozygous for blue skin Heterozygous offspring are called hybrids because their alleles are different A “zeedonk” is a zebra/donkey hybrid

Mendel’s Law of Independent Assortment Genes for different traits are inherited independently of each other Example: You have brown hair (Bb) and freckles (Ff) You can pass on to your children one of the following combinations: B + F, B + f, b + F, b + f

Genes, Chromosomes, and Numbers Diploid cell: has 2 of each kind of chromosome One came from mom, one came from dad All body cells, except gametes, are diploid cells When they divide, this is called mitosis

Genes, Chromosomes, and Numbers Haploid cell: has 1 of each kind of chromosome Gametes are haploid cells When they divide, this is called meiosis

Genes, Chromosomes, and Numbers Each type of organism has a specific number of chromosomes (humans have 46 chromosomes)

Genes, Chromosomes, and Numbers Homologous chromosomes: 2 of the same type of chromosome in a diploid cell Have genes for the same traits, but might have different alleles for the same gene Ex: Genes are for eye color, but blue eye color allele is on 1 chromosome and brown eye color allele is on the other chromosome