classical genetics gregor mendel. the work of gregor mendel genetics: the scientific study of...

Classical Genetics

Gregor Mendel

The Work of Gregor Mendel

Genetics: the scientific study of heredity, or how traits are passed from one generation to the next

Gregor Mendel’s Peas- Mendel was an Austrian monk who is credited as the “father of genetics.”


- Mendel began working with pea plants that were true-breeding, meaning that if allowed to self pollinate, they would only produce offspring identical to themselves

-ex. Tall plants produce tall plants, green seeded plants produce green seeded plants


Genes and Dominance- Mendel studied 7 different plant traits. Traits are characteristics such as height or flower color.


Seed Shape Flower

PositionSeed CoatColor

Seed Color Pod Color Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall


- Mendel called the original plants the P (parent) generation. The offspring were the F1 (first filial) generation .- the offspring of crosses between parents of different traits are called hybrids


Mendel's F2 Generation

P GenerationF1 Generation

Tall Tall Tall Tall Tall TallShort Short

F2 Generation

11-1 The Work of Gregor Mendel

From his experiments, Mendel drew two conclusions1) biological inheritance is determined by factors that are passed from one generation to the next. Today we call these factors genes.

- the different forms of a gene are called alleles


ex. gene (trait) is eye coloralleles (forms) are blue,

brown, green, etc.2) the second conclusion is called the principle of dominance- the principle of dominance states that some alleles are dominant and others are recessive


Segregation- Mendel saw that some forms of traits would disappear during the F1 generation, but reappear during the F2 generation- he explained this by showing that the alleles segregated during the formation of gametes, or sex cells.

Section QuizGametes are also known as

genes. sex cells. alleles. hybrids.

Section QuizThe offspring of crosses between parents

with different traits are called alleles. hybrids. gametes. dominant.

Section QuizIn a cross of a true-breeding tall pea plant

with a true-breeding short pea plant, the F1 generation consists of

all short plants. all tall plants. half tall plants and half short plants. all plants of intermediate height.

Section QuizIf a particular form of a trait is always

present when the allele controlling it is present, then the allele must be

mixed. recessive. hybrid. dominant.

Probability and Punnett Squares

Genes and Probability- the likelihood that an event will occur is called probabilityex. a coin landing on heads has a probability of 50%- the principle of probability can be used to predict the outcome of genetic crosses


Punnett squares- the gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square


Organisms that have two identical alleles for a particular trait are called homozygous.ex. TT

Organisms that have two different alleles for a particular trait are called heterozygousex. Tt


The physical characteristics of an organism are called its phenotypeex. tall plant

The genetic makeup of an organism is its genotypeex. TT or Tt

Section QuizProbability can be used to predict

average outcome of many events. precise outcome of any event. how many offspring a cross will produce. which organisms will mate with each other.

Section QuizCompared to 4 flips of a coin, 400 flips of

the coin is more likely to produce about 50% heads and

50% tails. less likely to produce about 50% heads and

50% tails. guaranteed to produce exactly 50% heads

and 50% tails. equally likely to produce about 50% heads

and 50% tails.

Section QuizOrganisms that have two different alleles

for a particular trait are said to be hybrid. heterozygous. homozygous. recessive.

Section QuizTwo F1 plants that are homozygous for

shortness are crossed. What percentage of the offspring will be tall?

100% 50% 0% 25%

Exploring Mendelian Genetics

Independent assortment- the principle of independent assortment states that genes for different traits can segregate independently during the formation of gametesex. Seed color does not depend on seed shape


Beyond dominant and recessive alleles- some alleles are neither dominant nor recessive , and many traits are controlled by multiple alleles or multiple genes


Incomplete dominance or Codominance- the heterozygous phenotype is somewhere between the two homozygous phenotypesex. red flower + white flower = pink

Punnett square animation


Multiple alleles- multiple alleles contribute to the phenotype ex. Blood type (i, IA, IB)Type O = i iType A = IA IA or IA iType B = IB IB or IB iType AB = IA IB


Polygenic traits- two or more genes control the outcome of a particular traitex. Skin color in humans is controlled by the combinations of 4 different genes

Section QuizIn four o'clock flowers, the alleles for red

flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have

pink flowers. white flowers. half white flowers and half red flowers. red flowers.

Section QuizMendel's principles apply to

pea plants only. fruit flies only. all organisms. only plants and animals.

Human Heredity

Human ChromosomesA typical human body cell contains

46 chromosomes- 44 autosomes and 2 sex chromosomes

Chromosomes are arranged in a karyotype, a picture of the chromosomes

Human Heredity

Human Heredity

Males and females differ in the sex chromosomes they contain- males are XY- females are XX

All egg cells carry a single X chromosome. However, half of all sperm cells carry a X chromosome while half carry a Y chromosome.

Human Heredity

Human Heredity

Human TraitsScientists use a pedigree to help

study how traits are passed from one generation to the next.

Pedigree: a chart which shows the relationships within a family

Pedigree animation

Human HeredityCircle = Female

Square = Male

Marriage lineParental line

carrier of the trait

shaded = express the trait

not shaded = does not express the trait

Human Heredity

Since most human traits are polygenic (many genes), they can not be traced to a single parent

Many genes have been discovered through the study of genetic disorders- they can be dominant or recessive

Human Heredity

In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder

Human Heredity

Cystic Fibrosis- caused by a recessive allele on chromosome 7- causes digestive and respiratory problems- only half of people with CF live into their 20s

Human Heredity

Human Heredity

Sickle Cell Disease- causes hemoglobin to be less soluble- changes the shape of red blood cells; become bent into the sickle-shape

Human Heredity

Malaria and the Sickle Cell Allele

Regions where malaria is common

Regions where the sickle cell allele is common

Section QuizA chromosome that is not a sex

chromosome is know as a(an) autosome. karyotype. pedigree. chromatid.

Section QuizAn individual with a blood type phenotype

of O can receive blood from an individual with the phenotype

O. A. AB. B.

Human Chromosomes

Human genes and chromosomes- on each chromosome there is the information for several hundred genes

ex. Gene for ALS is on 22nd chromosome

Human Chromosomes

Sex-linked genes: genes located on the X or Y chromosomeex. colorblindness, hemophilia, muscular dystrophy

Males have only 1 X chromosome and cannot be heterozygous for the trait. Females can be carriers (heterozygous).

Human Chromosomes

Father(normal vision)

ColorblindNormal vision

Mother (carrier)

Daughter(normal vision)

Son(normal vision)

Daughter(carrier)

Son(colorblind)

Male

Female

Human Chromosomes

Chromosomal disordersThe most common error occurs

when homologous chromosomes fail to separate during meiosis. This is called nondisjunction.

Human Chromosomes

Homologous chromosomes fail to separate

Meiosis I:Nondisjunction

Meiosis II

Human Chromosomes

Human Chromosomes

If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.- Down syndrome results from a nondisjunction of the 21st chromosome- Turner’s syndrome (XO) and Klinefelter’s syndrome (XXY)

classical genetics gregor mendel. the work of gregor mendel genetics: the scientific study of...

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