4-1 NotesFoundations 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.

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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 HeightT (tall)

t (short)

TTttTt

Mendel’s Experimental Results

• When organisms reproduce, each gamete—sperm or egg—contributes one factor for each trait.

orT

T

ort

t

T

t

t

T

or

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

• Y = yellow (dominant)

• y = green (recessive)

• ___ 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?

A inheritance

B genetics

C heredity

D allele

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

4.1 Foundations of Genetics

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

C flower position

D flower shape

SCI 2.c

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.

SCI 2.d