Inheritance (B)Inheritance (B)

DNA, Genes DNA, Genes

and Chromosomsesand Chromosomses

Learning Intention

• Identify factors that are due to genes and those due to environmental influences.

The study of inherited characteristics and

of those factors that determine or affect

inheritance.

Genetics

Meet our Mr Men And our Little Misses

Now lets meet their children!

Who do you think are his parents? Write the answers in your book.

Who do you think are her parents? Write the answers in your book.

Who do you think are his parents? Write the answers in your book.

Who do you think are his parents? Write the answers in your book.

Who do you think are her parents? Write the answers in your book.

Who do you think are her parents? Write the answers in your book.

What did we learn from this?

• Children inherit features from their parents

• If two parents have a certain characteristic then their child may show it even more (e.g. Mr Small + Little Miss Tiny = Mr Very Small!)

• Some things such as glasses, scars and muscles we get from our environment, they are not inherited.

Nucleus• The nucleus carries

genetic information which controls the characteristics of the organism.

• The structures which carry this information are called chromosomes.

Chromosomes• The gene is the unit of inheritance, and each

chromosome may have several thousand genes.

• We inherit particular chromosomes through the egg of our mother and sperm of our father.

• The genes on those chromosomes carry the code that determines our physical characteristics.

Physical Characteristics• Some physical characteristics, like eye

colour, are controlled by genes.

• Other physical characteristics are controlled by the environment.

• Can you think of a physical characteristic that isn’t controlled by genes?

Learning Intention• Define the term genotype and

phenotype.

Phenotypes• Each characteristic may display several

possible traits or versions. e.g. hair colour can be brown, black or red

• Each of these is called a PHENOTYPEPHENOTYPE

Phenotype• Leaf shape in plants, coat colour in

guinea pigs, wing type in fruit flies and eye colour in humans are all examples of physical characteristics.

• These physical characteristics make up the organisms phenotype.

Genotype• The phenotype (physical

appearance) that you have is controlled by the genes that you inherit from your parents.

• The combination of genes that you have is called your genotype.

Genes• We have two copies of every chromosome,

this means we have two copies of every gene.

Chromosome 1

Chromosome 1

1st gene for eye colour

2nd gene for eye colour

Alleles• The different forms of a gene are called

alleles.• For example the gene that controls eye colour

has different alleles blue, green or brown.

Blue form eye gene

Green form eye

gene

Brown form eye

gene

Alleles• If you inherit a blue allele from

your mum and a brown allele from your dad then you will have brown eyes.

• This is because some alleles are DOMINANT over others.

Dominant or recessive• Alleles can be dominant or recessive.

• Alleles which show up in the appearance of an organism are said to be dominant.

• Alleles which do not show up in the appearance of an organism are said to be recessive.

Dominant or recessive?Allele for white fur

Allele for brown fur

Which allele is dominant white fur or brown fur?

Dominant or recessive?

Which allele is dominant green body or yellow body?

Allele for green body

Allele for yellow body

Learning Intention• Be able to solve simple genetic

problems.

Some definitions• Genes:

• Phenotype:

• Genotype:

Sections of DNA in a chromosome that control an inherited characteristic, such as, hair colour, flower colour, height, etc.

The observable characteristics (appearance) of an organism.

The complete set of genes possessed by an organism.

Alleles• When describing an allele, we give it a

letter.

• If it is dominant it gets a capital letter and if it is recessive it gets lower case of the same letter.

• e.g. in pea plants tall is dominant over dwarf, and so the tall allele is given the letter T and the dwarf allele is given t.

Alleles

BB bb

This mouse has two dominant brown alleles

This mouse has two recessive white alleles

Alleles

• The genotype of the organism is the alleles it carries for that particular characteristic.

• The genotype for this fly is Rr, this tells us that it has one red eye allele and one white eye allele.

Alleles• TT is a genotype and the plant will be tall.

• Tt is a genotype and the plant will be tall as T is dominant over t.

• tt is a genotype and the plant will be dwarf.

• What the plant actually looks like is called the phenotype.

Monohybrid cross• A monohybrid cross is

the study of the inheritance of one characteristic.

• Monohybrid crosses were first carried out by a monk called Gregor Mendel who worked on pea plants.

Mendel’s Pea Plant CrossesTall plant

Dwarf plant

ParentX

Offspring ALL Tall

F1X

F2

Tall DwarfTallTall

Phenotypic Ratio

3 Tall:1 Dwarf

X

X

parents (P)

second filial generation (F2)

members of F1 self-pollinated

F2 phenotypic ratio

first filial generation (F1)

3 tall : 1 dwarf

all tall

true breeding dwarf strain

true breeding tall strain

This type of experimental cross is called a monohybrid cross as it follows the inheritance of only one characteristic at a time.

Gregor Mendel

X

rrRR

XP

F1

rrRR

Rr Rr Rr

F1 F1XX

F2

Red 3 White 1

Rr Rr

Punnet square• Punnet squares allow us to figure out the

genotypes and phenotypes of the offspring in the F2.

XF1

Bb Bb

??

XF1

Bb BbB b

B BB Bb

b Bb bb

F2 genotype – BB, Bb, Bb, bb

F2 phenotype – 3 brown mice and one white mouse

F1

F2 genotype –

F2 phenotype –

X

Rr Rr

Ratio• In a cross where the 2 parents are

true-breeding, the expected phenotype ratio in the F2 generation is:

3:1

RecessiveDominant

Build a baby• Head: R= purple , r=yellow

• Body: B= blue, b=green

• Arms: A=orange , a =purple

• Legs: H=yellow, h=blue

• Eyes: E=pink , e=orange

• Nose: N = Green , n=yellow

• Mouth: P= pink p= purple

Build a baby

• What body colour is dominant, what letter is this represented by?

• Now take your baby and find it a partner.

• If they were to have babies of their own in the future, what colour of eyes might they have?

• Now do the same for body colour and arm colour.