4-1 Notes Foundations of Genetics Chapter 4 Lesson 1

Early Ideas About Heredity Combined genetic material from a sperm and an egg determines the traits or features of an offspring.

Early Ideas About Heredity Heredity is the passing of traits from parents to offspring.

Early Ideas About Heredity The idea of blending inheritance is offspring are a blend of genetic material from both parents. + =

Early Ideas About Heredity The genetic material mixed or blended like colors of paint.

Early Ideas About Heredity Over many generations, populations would eventually look alike.

Early Ideas About Heredity Blending inheritance cannot explain why some traits skip a generation.

Gregor Mendel and His Experiments Gregor Mendel was the first to record evidence that traits are determined by factors passed from parents to offspring. Mendel established the basic laws of heredity.

Gregor Mendel and His Experiments Genetics is the study of how traits of organisms are passed from parents to offspring.

Mendel’s Experimental Methods Mendel conducted breeding experiments by studying seven traits of pea plants and each trait had only two variations.

Controlled Experiments Mendel controlled fertilization in the pea plants, allowing him to see how traits pass from one generation to another.

Controlled Experiments Mendel allowed some flowers to self-fertilize.

Controlled Experiments He also performed cross-fertilization by transferring pollen from one pea flower to another.

Mendel’s Unique Methods Used true-breeding plants for each trait—plants that always produce offspring with that trait when they self-pollinate

Mendel’s Unique Methods Recorded the inheritance of traits for several generations Used a mathematical approach

Mendel’s Experimental Results Mendel concluded that two factors control each inherited trait. Plant Height T (tall) t (short) TT tt Tt

Mendel’s Experimental Results When organisms reproduce, each gamete— sperm or egg—contributes one factor for each trait. T t T t or or or T t t T TT tt Tt Tt

Dominant Factors A genetic factor that blocks another genetic factor is called dominant. A dominant trait is observed when offspring have one or two dominant factors. Indicated by the capital letter (Y for yellow) Y YY or Yy

Recessive Factors A genetic factor that is hidden by the presence of a dominant factor is recessive. A recessive trait can be observed only when two recessive genetic factors are present in offspring. Indicated by the lowercase letter (y for green) y yy

Modern Definitions of Mendel’s Ideas Mendel did not know about DNA or how cells reproduce, but his ideas about inheritance are still true today.

Genes and Alleles A gene is a section of DNA that has information about a trait in an organism.

Genes and Alleles Each form of a gene with different information is called an allele. Alleles A or a D or d T or t

Genes and Alleles

Phenotype and Genotype The observable traits and all characteristics of an organism make up the organism’s phenotype.

Phenotype and Genotype The alleles that make up an organism is the organism’s genotype. The alleles of a particular gene is that gene’s genotype.

Homozygous and Heterozygous Genotypes Because eukaryotes have pairs of chromosomes, a genotype for a gene has two alleles.

Homozygous and Heterozygous Genotypes If the two alleles have the same information, the genotype is homozygous.

Homozygous and Heterozygous Genotypes If the two alleles have different information, the genotype is heterozygous.

Homozygous and Heterozygous Genotypes

Symbols 3 2 Y = yellow (dominant) y = green (recessive) Genotype ___ different genotypes & ___ different phenotypes Genotype Phenotype YY (homozygous dominant) yellow (purebred) yy (homozygous recessive) green (purebred) Yy (heterozygous) yellow (hybrid) 3 2

Mendel’s Law of Segregation During meiosis is when gametes (sperm/egg) form. The two factors for each trait segregate (separate) from each other during meiosis.

Mendel’s Law of Segregation Each set of chromatids separates into different gametes. Each gamete receives only one allele.

Mendel’s Law of Independent Assortment The factors for one trait separate independently of how factors for other traits separate

Mendel’s Law of Independent Assortment A daughter cell might receive the A or a chromosome from pair 1 and the B or b chromosome from pair 2.

Mendel’s Law of Independent Assortment This results in four possible allele combinations (for two homologous pairs of chromosomes).

Importance of Mendel’s Genetic Studies In the 1860s, no one knew about chromosomes or meiosis so it was hard to understand Mendel’s discoveries. All the research of modern genetics is based on Mendel’s conclusions from his work with pea plants.

What is the passing of traits from parents to offspring called? 4.1 Foundations of Genetics What is the passing of traits from parents to offspring called? A inheritance B genetics C heredity D allele

What are the alleles that make up an organism called? A genes 4.1 Foundations of Genetics What are the alleles that make up an organism called? A genes B genotype C phenotype D factors

4.1 Foundations of Genetics If two alleles for a gene have the same information, what kind of genotype does that gene have? A homologous B recessive C heterozygous D homozygous

What is the term for the idea that offspring are a blend of genetic material from both parents? A polygenic inheritance B sex-linked inheritance C maternal inheritance D blending inheritance

What type of alleles can only be observed in the phenotype when they are present as a homozygous genotype? A dominant B recessive C inherited D heterozygous

What is the term for the idea that inheritance of one trait is not influenced by inheritance of another trait? A law of independent assortment B law of heredity C law of segregation D maternal inheritance

Which pea trait did Mendel not study? A seed color B pod color SCI 2.c Which pea trait did Mendel not study? A seed color B pod color C flower position D flower shape

Which does NOT describe Mendel’s experiments? SCI 2.d Which does NOT describe Mendel’s experiments? A Mendel observed several generations of plants. B Mendel chose pea plants because they reproduce quickly. C Mendel counted small numbers of offspring. D Mendel used true-breeding plants.