genetics: the science of heredity mendel’s work probability and heredity the cell and inheritance...

Genetics: The Science of Heredity

Mendel’s Work

Probability and Heredity

The Cell and Inheritance

The DNA Connection

Table of Contents


Mendel’s Work pg 76

His observations revolutionized the study of HEREDITY

He asked why his pea plants had different characteristics


BEGIN NOTESMendel’s Laws of Heredity

1. Why Mendel Succeeded

a. Gregor Mendel-Father of Genetics

b. 1st studies of heredity-the passing of

characteristics (traits) to offspring such as bone structure, and eye color.

c. Genetics-Study of Heredity


Mendel’s Experiment

2. Mendel’s Experiment Crossing Pea Plants

A. crossed plants with contrasting traits (Tall and short).

B. Controlled the fertilization process of this peas plants. He removed pollen from a flower on one plant and transferred it to another

C. Started experiment with Purebred plants (Tall from Tall plants and short from short plants)

D. Purebred-organisms are the offspring of many generations that have the same trait.

Genetics: The Science of Heredity - Mendel’s Work

Crossing Pea Plants

Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.


P Generation (purebred) trait

Purebred Tall Purebred short

TT tt

cross fertilization

Capital Letter T = Dominate Trait

Lower Case Letter t = recessive trait


3. The 1st Generation

A. Mendel crossed two plants- 1 tall and 1 short. (purebred Tall and short) called the parental generation (P Generation)

B. The off spring from the P Generation were all called the 1st filial generation(F1 Generation)

C. All the offspring were tall (the short plants were totally excluded)

WHY???????????????????????????


F1 Generation

TT tt

cross fertilization

Created the F1 Generation

Tt, Tt, Tt, Tt

All the plants are _________________?




4. The 2nd Generation

A. 1. Next, Mendel crossed two plants from the F1 Generation

B. 2. The offspring from this cross are called the 2nd filial generation (F2 Generation)

C. Mendel found that ¾ of the offspring were Tall and ¼ were short (the short plants reappeared).


F2 Generation

Tt Tt

cross fertilization

Created the F2 Generation

Tt, TT, TT, tt

3 out of 4 plants are _________________?

1 out of 4 plants are _________________?




Mendel’s Experiments

In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants. (DRAW PICTURE BELOW)


Brain Pop & Quiz

Brain Pop Heredity


Alleles~Alternate forms of a gene are called alleles.

~Alleles are represented by a one or two letter symbol.

(e.g. T for tall and t for short)

~These two alleles are now known to be found on copies of chromosomes-one from each parent.


Dominant and Recessive Alleles

Mendel studied several traits in pea plants.


Dominant and Recessive Alleles

Dominant: A gene that is always express and hides others

It is present and the trait always shows up and is always

represented by a capital letter.

Recessive: A gene that is only expressed when a dominant

gene is not present. A recessive trait will only be expressed if both alleles are recessive. They are represented by a lower case letter.


GeneticsDominant and Recessive Genes

A dominant gene will always mask a recessive gene.

A “widows peak” is dominant, Widows Peak

not having a widows peak is recessive.

If one parent contributes a gene for a widows peak, and the other parent doesn’t, the offspring will have a widows peak.


Genetics~Punnet Square - A tool we use for predicting the traits of an offspring

~Letters are used as symbols to designate genes

~Capital letters are used for dominant genes

~Lower case letters are used for recessive genes

~Genes always exist in pairs


GeneticsAll organisms have two copies of each gene, one contributed by

the father, the other contributed by the mother.

Homozygous - Two copies of the same gene

Heterozygous - Two different genes


GeneticsFor the widows peak:

WW - has a widows peak Homozygous dominant

Ww - has a widows peak Heterozygous

ww - no widows peak Homozygous recessive

Genetics: The Science of Heredity - Probability and Heredity

A Punnett Square

The diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.

Genetics: The Science of Heredity - Probability and Heredity

Phenotypes and Genotypes

An organism’s phenotype is its physical appearance, or visible traits, and an organism’s genotype is its genetic makeup, or allele combinations.

Genetics: The Science of Heredity - The Cell and Inheritance

MeiosisDuring meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.


Punnett Square

A Punnett square is actually a way to show the events that occur at meiosis.


A Lineup of Genes

Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.

Genetics: The Science of Heredity - The DNA Connection

Mutations

Mutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.


End of Section:Graphic Organizer

genetics: the science of heredity mendel’s work probability and heredity the cell and inheritance...

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