BIOLOGY CHAPTER 8Heredity

8.1 OBJECTIVES

Discuss Mendel’s experiments and his results.

Explain the three principles of genetics Mendel obtained through his experiments.

Solve genetics problems using Punnett Squares.

8.1 PRINCIPLES OF GENETICS

Discuss Mendel’s experiments and results. Explain the three principles of genetics

Mendel obtained through his experiments. Solve genetics problems using Punnett

squares.

PRINCIPLES OF GENETICS

The passing of traits from parents to offspring is termed heredity.

Can we predict certain traits? Can we determine what types of genetic

information parents have by looking at certain traits of the offspring?

We can answer these questions through genetics – the science of heredity.

ORIGIN OF GENETICS

Father of genetics: Gregor Mendel (1882-1884)

Tended to a garden of pea plants in a monastery.

Published results from 8 years of research, only to be ignored until 1900.

MENDEL’S EXPERIMENTS

Peas are grown easily and produce large numbers of offspring in a short time.

Chose 7 traits to study:

Seed Shape

Seed Color

Flower Color

Flower Position

Pod Color

Pod Shape

Plant Height

Dominant Trait

Round Yellow

Purple Axial (side) Green Inflated Long

Recessive Trait

Wrinkled Green

White Terminal (tips)

Yellow Constricted Short

MENDEL’S PROCESS

Mendel crossed pea plants w/ different traits. Offspring of parental cross were called F1

Offspring of F1 crosses called F2. He noted for each trait, there was a dominant

and recessive form. In his crosses, recessive trait disappeared in

F1 generation and then reappeared in F2.

MENDEL’S HYPOTHESIS

He reasoned that for every trait, there must be a pair of factors.

He called them characters, but we now know them as genes.

One gene came from each parent.

PUNNETT SQUARES

PUNNETT SQUARES

PUNNETT SQUARES

THE TEST OF SEGREGATION

He predicted if the F1 purple flowered plants were crossed with white flowered plants, he would get ratios different from any of his previously obtained ratios.

TERMINOLOGY

Each alternative form of a gene for a certain trait are called alleles.

Combination of genes for a given trait referred to as genotype. Example: WW and Ww

The physical appearance of a trait is the phenotype. Example: Blue and brown eyes.

Homozygous = two of same alleles: WW or ww (homozygous dominant and homozygous recessive)

Heterozygous = two different alleles: Ww

TWO TRAITS (DIHYBRID CROSSES)

TWO TRAITS (DIHYBRID CROSSES)

TWO TRAITS (DIHYBRID CROSSES)

8.2 SOLVING GENETICS PROBLEMS

Objectives: Apply the rules of probability to solve

genetics problems. Demonstrate the inheritance of traits

resulting from incomplete dominance, codominance, and multiple alleles.

PROBABILITY

What is the probability of getting heads or tails when you toss a coin?

There is a list of steps to follow on page 208 in text, but we have already been doing this.

Remember, we can find either genotypic or phenotypic ratios.

INCOMPLETE DOMINANCE: 4 O’CLOCK PLANTS AS AN EXAMPLE

MULTIPLE ALLELES: HUMAN BLOOD TYPES

8.3 THE CHROMOSOME THEORY OF HEREDITY

Walter Sutton’s work showed good evidence that genes reside on chromosomes.

Some genes appear only on sex chromosomes.

XX = female and XY = male in humans. Different combinations for different species. Example: Grasshoppers X = male and YY =

female. Sex-linked traits are traits that result from

genes on the sex chromosomes.

SEX-LINKED TRAITS IN HUMANS

Hemophilia – gene is a recessive gene found on the X chromosome. Mostly, males get the disease.

Color-blindness is the same way.

MANY GENES – ONE EFFECT

Height, hair, eye, and skin color all controlled by multiple alleles.

Sample genotypes: AABBCCDD AaBbCcDd Aabbccdd

Modifier genes can also impact things like eye color. Brown, blue, hazel, green, mixed etc.