mendel & the origins of genetics. heredity and genetics what is heredity? the passing of genetic...

MENDEL & THE ORIGINS OF GENETICS

Heredity and Genetics

What is Heredity?The passing of genetic

traits from parent to offspring

What is Genetics?

The branch of Biology that

studies heredity

Gregor Mendel

The Father

of Geneti

cs

Gregor Mendel studied genetics in the 1800’s.

He was born in Austria to peasant parents who worked as gardeners.

He studied at the University of Vienna and later became a monk.

Conducted experiments in the garden studying traits in pea plants.

Observed & recorded traits passed from parents to offspring.

Mendel Brainstorm

What were Mendel’s Experiments?

What characteristics did Mendel study?

Mendel’s ExperimentsGregor Mendel

carried out a series of experiments related to how certain characteristics are inherited in pea plants.

The characteristics that Mendel studied include…

flower color flower position plant height pod appearance pod color seed texture seed color

So why did Mendel pick pea plants?

1. Many traits exist in two clearly different forms

2. The mating or crossing of two plants can easily be controlled

3. Pea plants are small, easy to grow, mature quickly, and produce many offspring

Mendel’s Experiments

P Generation (Parental Generation) Mendel allowed two plants to self-pollinate until

all offspring displayed only one characteristic (example, all purple) – this is called true breeding.

A true breeding plant will only allow one trait to show through because it should be either 100% homozygous dominant (purple) or 100% homozygous recessive (white).


He then picked two parents, each with contrasting traits (one purple and one white) and cross-pollinated them.

F1 Generation

The offspring of the Parental Generation which Mendel cross-bred; this generation only expressed one trait (the dominant trait, purple)


Next, he allowed F1 generation plants to self-pollinate.

F2 Generation

The self-pollinating offspring of the F1 Generation; this generation expressed both traits again, although the dominant (purple) trait was expressed more often (3:1)

Mendel’s Experiments - Hypotheses

An individual has two copies of a gene – one from each parent.

There are different versions of each gene. For example, the gene for flower color in pea plants can either be purple or white, represented by letters; P = purple and p = white.

Alleles the different versions of the gene;

represented by letters

One allele is dominant, one is recessive…

Dominant: expressed form of trait (capital allele)

Recessive: not expressed form of trait (lower case allele)

Mendel’s Experiments - Conclusions

Genotype the set of alleles that an individual has

(the actual genes)Ex: BB, Tt, or qq

Phenotype the physical appearance of a trait (how it

actually appears)Ex: Brown eyes or blue eyes; tall or

short

Homozygous Having identical alleles for a trait; either two

dominant alleles or two recessive alleles

Homozygous Dominant = BB or TT or QQ

Homozygous Recessive = bb or tt or qq

Heterozygous Having two different alleles

Bb or Tt or Qq

Mendel’s BIG Conclusions…The Laws of Heredity

Law of Segregation

Two alleles for a trait separate when gametes are formed

Law of Independent Assortment

The inheritance of one trait does not influence the inheritance of another trait

These both occur during Meiosis!

Mendel’s Contributions

On the left side of your IN, write a short paragraph about the importance of Mendel’s research.

STUDYING HEREDITY

Punnett Square

Simple diagram used to predict expected result of a genetic cross

Genetic CrossHh x hh

What is the genotype of

parent 1?

What is the genotype of

parent 2?

Heterozygous Homozygous Recessive

Hh

Hh

hh

hh

Punnett Squares consider all possible combination of gametes for that particular cross

Punnett Squares – Monohybrid Cross

A cross that considers ONE pair of contrasting traits between two individuals

Cross the following!Heterozygous Male x Heterozygous

FemaleGg x GgFrog Color

Key

G – Greeng- brown

G

G

g

g

GG

Gg

Gg

gg

What is the probability that the offspring is heterozygous?

50% What is the probability that the offspring is

homozygous recessive?

25%

What is the probability that the offspring is green?


brown?

25%


Cross the following!Heterozygous Female x Homozygous

Recessive Male

Gg x gg

Frog Color Key

G – Greeng- brown

G g

g

g

Gg

Gg

gg

gg

What is the probability that the offspring is green?


brown?50%


Cross the following!Homozygous Dominant Female x Homozygous

Recessive Male

RR x rr

Seed of Pea Plants Key

R – Roundr- Wrinkled

r r

R

R RrRr

RrRr

What is the genotype of all of the offspring?Heterozygous

What is the probability the offspring’s phenotype is Round?

100%


Try 1 more cross!Heterozygous Male x Heterozygous

FemaleRr x Rr

Seed of Pea Plants Key

R – Roundr- Wrinkled

R

R

r

r

RR

Rr

Rr

rr

How many offspring would you expect to have the: Genotype RR1/4 or 25% Genotype Rr2/4 or 1/2 or 50% Genotype rr1/4 or 25%

What is the genotypic ratio?

1:2:1

How many offspring would have the following phenotype? Round Seeds 3/4 or 75% Wrinkled Seeds 1/4 or 25%

What is the phenotypic ratio?

3:1

A test cross can be performed to determine whether a parent with a dominant phenotype is homozygous dominant or heterozygous.

In a test cross, an individual whose phenotype is dominant, but whose genotype is unknown, is crossed with a homozygous recessive individual. One can then look at the offspring to determine the genotype of the parent.

Test Cross

Test Cross - examples

P

p

p

Unknown withdominant phenotype

Hom

ozy

gous

rece

ssiv

e

Pp=purpl

e

Pea Plant Flower ColorP = purplep = white

Pp= purpl

e

purple

purple

?So if w

e get 4

purple

offspring,

what must

the other

allele be?

PPp=

Pp=

mendel & the origins of genetics. heredity and genetics what is heredity? the passing of genetic...

Documents