MENDELIAN GENETICS

Genetics is everywhere these days – and it will continue as a dominant force in biology and society for decades to come.

Gregory Mendel – 1822- 1884

•Australian monk

•Afterwards became Father of modern genetics

•Researched with pea plants

•Developed ideas of dominance and trait segregation

How Genetics Began The passing of traits to the next generation

is called inheritance, or heredity. Mendel performed cross-pollination in pea

plants. Mendel followed various traits in the pea

plants he bred.

MENDELIAN GENETICS

Mendel studied seven different traits. Seed or pea color Flower color Seed pod color Seed shape or texture Seed pod shape Stem length Flower position

MENDELIAN GENETICS

The second filial (F2) generation is the offspring from the F1 cross.

MENDELIAN GENETICS

Mendel crossed a pure yellow pea with a pure green pea

The offspring of this P cross are called the first filial (F1) generation.

Genes in Pairs

Allele

An alternative form of a single gene passed from generation to generation

They can be Dominant or Recessive

MENDELIAN GENETICS

DominanceAn organism with two of the same alleles for

a particular trait is homozygous.An organism with two different alleles for a

particular trait is heterozygous.

MENDELIAN GENETICS

Genotype and PhenotypeAn organism’s allele pairs are called its

genotype.The observable characteristic or outward

expression of an allele pair is called the phenotype.

An example of Genotype is Yy An example of Phenotype is yellow

MENDELIAN GENETICS

Mendel’s Law of Segregation Two alleles for each trait separate during meiosis. During fertilization, two alleles for that trait unite. Heterozygous organisms are called hybrids.

MENDELIAN GENETICS

Law of Independent Assortment Random distribution of alleles occurs during

gamete formation Genes on separate chromosomes sort

independently during meiosis. Each allele combination is equally likely to

occur.

MENDELIAN GENETICS

Genetic Recombination The new combination of genes produced by

crossing over and independent assortment

MENDELIAN GENETICS

Combinations of genes due to independent assortment can be calculated using the formula 2n, where n is the number of chromosome pairs.

Monohybrid Cross

A cross that involves hybrids for a single trait is called a monohybrid cross.

MENDELIAN GENETICS

Dihybrid Cross The simultaneous inheritance of two or more

traits in the same plant is a dihybrid cross. Dihybrids are heterozygous for both traits.

MENDELIAN GENETICS

Probability

• The likelihood that a particular event will occur• Example: What is the probability that a coin

when flipped will be heads? .. ½ X ½ = 50%

• What is the probability that a coin when flipped will be heads three times in a row?

½ X ½ X ½ = 1/8 or 1 out of 8 chance

MENDELIAN GENETICS

Punnett Squares

Predict the possible offspring of a cross between two known genotypes

Shows probability

Punnett Square—Dihybrid Cross

Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.

The resulting phenotypic ratio is 9:3:3:1.

Gene Linkage The linkage of genes on a chromosome results

in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently.

Polyploidy Polyploidy is the occurrence of one or more extra

sets of all chromosomes in an organism.

A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes.

Complex Patterns of Inheritance

Incomplete Dominance The heterozygous phenotype is an

intermediate phenotype between the two homozygous phenotypes.

Codominance

Both alleles are expressed in the heterozygous condition.

Complex Patterns of Inheritance

Polygenic Traits Polygenic traits arise from the interaction of

multiple pairs of genes.

Complex Patterns of Inheritance

Multiple Alleles Blood groups in

humans ABO blood groups

have three forms of alleles.

Complex Patterns of Inheritance

Coat Color of Rabbits Multiple alleles can demonstrate a hierarchy

of dominance. In rabbits, four alleles code for coat color:

C, cch, ch, and c.

Complex Patterns of Inheritance

Coat Color of Rabbits

Light gray

Dark gray Himalayan

Albino

Chinchilla

Complex Patterns of Inheritance

Dosage Compensation The X chromosome carries a variety of

genes that are necessary for the development of both females and males.

The Y chromosome mainly has genes that relate to the development of male characteristics.

Complex Patterns of Inheritance

Sex Determination Sex chromosomes

determine an individual’s gender.

Complex Patterns of Inheritance

Sex-Linked Traits Genes located on the X chromosome

Red-green color blindness Hemophilia

Complex Patterns of Inheritance

Sex-Linked Traits

Environmental Influences Environmental factors Diet and exercise Sunlight and water Temperature

Complex Patterns of Inheritance

Pedigrees A diagram that traces the inheritance of a

particular trait through several generations

Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.

Karyotype Studies

Images of chromosomes stained during metaphase

Chromosomes are arranged in decreasing size to produce a micrograph.

Cystic Fibrosis Affects the mucus-producing glands,

digestive enzymes, and sweat glands Chloride ions are not absorbed into the

cells of a person with cystic fibrosis but are excreted in the sweat.

Without sufficient chloride ions in the cells, a thick mucus is secreted.

Basic Patterns of Human Inheritance

Basic Patterns of Human Inheritance

Recessive Genetic Disorders

A recessive trait is expressed when the individual is homozygous recessive for the trait.

Albinism Caused by altered genes, resulting in the

absence of the skin pigment melanin in hair and eyes

White hair Very pale skin Pink pupils

Basic Patterns of Human Inheritance

Tay-Sachs Disease Caused by the absence of the enzymes

responsible for breaking down fatty acids called gangliosides

Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.

Basic Patterns of Human Inheritance

Dominant Genetic Disorders Huntington’s disease affects the nervous

system. Achondroplasia is a genetic condition that

causes small body size and limbs that are comparatively short.

Basic Patterns of Human Inheritance

Basic Patterns of Human Inheritance

Sickle-cell Disease Changes in hemoglobin

cause red blood cells to change to a sickle shape.

People who are heterozygous for the trait have both normal and sickle-shaped cells. Sickle cell

Normal red blood cell

7766x

Basic Patterns of Human Inheritance

1. A2. B3. C4. D

CDQ 1

A. #B. xC. rD. n

Which symbol is used to represent the number of chromosomes in a gamete?

Chapter Diagnostic Questions

1. A2. B3. C4. D

CDQ 2

Chapter Diagnostic Questions

A. Felix MendelssohnB. Gregor MendelC. Dr. Reginald PunnettD. Albert Einstein

Name the person known as the father of genetics.

1. A2. B3. C4. D

CDQ 3

Chapter Diagnostic Questions

A. gameteB. hybridC. phenotypeD. genotype

Which term refers to the outward expression of an allele pair?

1. A2. B3. C4. D

FQ 1

Segments of DNA that control the production of proteins are called _______.

A. chromatidsB. chromosomesC. genesD. traits

Formative Questions

1. A2. B3. C4. D

FQ 2

Formative Questions

What is the term for a pair of chromosomes that have the same length, same centromere position, and carry genes that control the same traits?

A. diploidB. heterozygousC. homozygousD. homologous

1. A2. B3. C4. D

FQ 3

Formative Questions

How does the number of chromosomes in gametes compare with the number of chromosomes in body cells?

A. Gametes have 1/4 the number of chromosomes.

B. Gametes have 1/2 the number of chromosomes.

C. Gametes have the same number of chromosomes.

D. Gametes have twice as many chromosomes.

1. A2. B3. C4. D

FQ 4

Formative Questions

What type of organisms only reproduce asexually?

A. bacteriaB. protistsC. plantsD. simple animals

1. A2. B3. C4. D

FQ 5

What is the name for different forms of a single gene that are passed from generationto generation?

A. allelesB. genotypesC. phenotypesD. traits

Formative Questions

1. A2. B3. C4. D

FQ 6

Formative Questions

Which pair of alleles is heterozygous?

A. RRB. RrC. rrD. yR

1. A2. B3. C4. D

FQ 7

Formative Questions

In rabbits, gray fur (G) is dominant to black fur (g). If a heterozygous male is crossed with a heterozygous female, what is the phenotypic ratio of the possible offspring?

A. 1:1B. 1:2:1C. 2:1D. 3:1

1. A2. B3. C4. D

FQ 10

Formative Questions

What is the term for an organism that has one or more sets of extra chromosomes in its cells?

A. diploid B. gameteC. hybridD. polyploid

1. A2. B3. C4. D

Standardized Test Practice

STP 4

To which step in this process does the law of segregation apply?

A. grows into plantB. gamete formationC. fertilizationD. seed development