From Mendel to DNA. Recap from previous lessons 1.Mitosis produces daughter cells with: a.fewer...

From Mendel to DNA

Recap from previous lessons

1. Mitosis produces daughter cells with:

a. fewer chromosomes than the parent cell

b. more chromosomes than the parent cell

c. the same number of chromosomes as the parent cell

2. As a result of mitosis, how many cells are produced?

a. One

b. Two

c. Four

3. How many pairs of chromosomes does a human body cell contain?

a. 4

b. 23

c. 46

4. Which statement about sex chromosomes is correct?

a. Females are XY and males are XX.

b. Females and males are XX.

c. Females are XX and males are XY.

5. Where are the cell's chromosomes found?

a. In its nucleus.

b. In its cytoplasm.

c. In its mitochondria.

6. Compared to a body cell, a gamete contains:

a. Half the genetic information.

b. The same amount of genetic information.

c. Twice the genetic information.

Higher Questions

7. During meiosis:

a. No copies of the chromosomes are made.

b. Gametes are formed, each with a single set of chromosomes.

c. The cell divides five times to form four gametes.

8. As a result of meiosis, how many sex cells are produced?

a. One

b. Two

c. Four

Learning Objectives

1. To understand the work Mendel carried out and why its importance was not recognised until after his death.

2. To know why DNA fingerprinting is possible.

444444 44Gregor Mendel

One of the classic scientific experiments on inheritance was

performed by an Austrian monk named Gregor Mendel

(1822–1884)

Mendel’s work with garden peas…..

Why did Mendel choose the garden pea on which to perform his work?

Chromosomes o The 2 chromosomes in each pair carry information for the same characteristic

o Examples of characteristic include eye colour, hair colour etc...

o So each body cell has 2 sets of information for all of your characteristics

o One set is inherited from your mother the other from your father

One set of information for eye

colour from

mother

One set of information for eye

colour from

father

Inheritance of Characteristics

o Just like us, the pea plants chromosomes also come in pairs

o And just like us, each pair carries genes for the same characteristic

o Sometimes the form of these genes

are different and sometimes they are the same

o Different forms of genes are called alleles One set of

information from ‘mother’

One set of information from ‘father’


White and Purple

pea plant bred

together

All the offspring (F1 generation) are Purple


2 purple pea plants from the

F1 generation crossed

The offspring (F2 generation) are purple and white. Mendel wondered how white flowers could disappear for a generation but then come back


o The combination of alleles determines what our characteristics will be

o Alleles can be either Dominant or Recessive

o You will always see the effect of the dominant allele over the recessive one.

Allele Example o In pea plants Purple flowers are

dominant and white flowers are recessive

For a flower to be white it must have 2 white alleles. Since the white colour is recessive

For a flower to be purple it could have 2 purple alleles or one white and one purple allele. Since purple is the dominate colour

We can show inheritance of flower colour using a geneticdiagram. We use capital letters to represent the dominant allele and the same lower case letter to represent the recessive allele.

ppPP

Pp

ppPp

PpPP

Pp Pp

P

P

p

p

Mendel

Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,

1. When a tall pea plant was crossed with a dwarf pea plant – all offspring were tall pea plants (i.e. 100% identical)

2. When the two offspring (tall pea plants), three of the offspring were tall and one was a dwarf (i.e. 3:1)– why?

1. When a tall pea plant was crossed with a dwarf pea plant – all offspring were tall pea plants (i.e. 100% identical)

2. When the two offspring (tall pea plants), three of the offspring were tall and one was a dwarf (i.e. 3:1)– why?

Genetic Crosses


Tall x DwarfTall x Dwarf

TALL plants (TT)

T T

t

t

DWARF plants

(tt)

Tt Tt

Tt Tt

100 ‘Tt’

As ‘T’ is DOMINANT and ‘t’ is RECESSIVE,

All plants are TALL carriers.

Genetic Crosses


Tall Carrier x Tall CarrierTall Carrier x Tall Carrier

TALL CARRIER plants (Tt)

T t

T

t

TT Tt

Tt tt

TT = Tall

Tt = Tall

tt = dwarf

So 3:1

Genetic Crosses


Alleles are different forms of the same gene. Alleles are different forms of the same gene.

Normal Boring Hamster

B B

b

b

Wild Scatty

Hamster

Bb Bb

Bb Bb

All Bb

So, all are normal and boring hamsters.

Genetic Crosses


Bb x Bb – What are their offspring like?Bb x Bb – What are their offspring like?

B b

B

b

BB Bb

Bb bb

BB = boring

Bb =boring

bb = wild

So 3:1

Recessive

• He published a book of his findings in 1866, when he was 44 years old.

• People did not understand his theories as no one had seen chromosomes.

• He died 20 years later with no one taking notice of his work.

• 16 years after his death people could finally see chromosomes through a microscope and he was given the recognition for his findings.

Cystic Fibrosis


This is a genetic disorder of the cell membranes. It results in a thick sticky mucus in the

air passages and in the pancreas.

This is a genetic disorder of the cell membranes. It results in a thick sticky mucus in the

air passages and in the pancreas.

Huntington’s


This is a genetic disorder of the nervous system which

results in shaking, erratic body movements and eventually

severe mental deterioration.

This is a genetic disorder of the nervous system which

results in shaking, erratic body movements and eventually

severe mental deterioration.

Genetic Disorders


1. Cystic Fibrosis is caused by a recessive allele. For a child to have Cystic Fibrosis, but its parents not to have the

condition, what must the parent genetic code be? Draw a genetic diagram to explain your answer.

2. Huntington’s is a disease that is caused by a dominant allele. What is the chance of offspring having Huntington’s when one parent is normal and the other is a carrier/sufferer?

3. Before embryos are inserted back into the female in IVF, the embryo are screened for genetic disorders. Is the screening

of embryo’s right or wrong?

1. Cystic Fibrosis is caused by a recessive allele. For a child to have Cystic Fibrosis, but its parents not to have the

condition, what must the parent genetic code be? Draw a genetic diagram to explain your answer.

2. Huntington’s is a disease that is caused by a dominant allele. What is the chance of offspring having Huntington’s when one parent is normal and the other is a carrier/sufferer?

3. Before embryos are inserted back into the female in IVF, the embryo are screened for genetic disorders. Is the screening

of embryo’s right or wrong?

Cc x Cc

50% (Nn x nn)

Single-Trait Inheritance

1. Since one allele is inherited from each parent,

various genotypes are possible.

2. The dominant phenotype is expressed if the

offspring is either heterozygous or homozygous for the

dominant allele.

3. The recessive phenotype is expressed only if the

offspring is homozygous for the recessive allele.

4. When there are multiple alleles for a given

characteristic, the alleles have a dominance

hierarchy.

From Mendel to DNA. Recap from previous lessons 1.Mitosis produces daughter cells with: a.fewer...

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