1. Genetics and Inheritance
Specific Learning Objectives:
Explain the terms alleles, dominant, recessive, homozygous, heterozygous, genotype and phenotype
Complete and explain monohybrid crosses using a Punnett square

2. Different eye colours are produced because of the different amounts and patterns of pigment in the iris. The amount of pigment and the pattern of the pigment is determined by a person's genetic makeup. The DNA received from one's parents determines what colour eyes they will have.

3. Each human has 46 chromosomes located in the nucleus of the cell
Each human has 46 chromosomes located in the nucleus of the cell. These are divided into 23 pairs of chromosomes. A baby inherits one chromosome from each parent in each pair of chromosomes. A piece of DNA on a chromosome is called a gene. Genes are the basic unit of heredity, they determine many characteristics about a baby. Genes also come in pairs. Alleles are found in genes and determine the appearance of any characteristic. There are two alleles for each trait inherited. If the two alleles are the same then they are homozygous for that gene. If the alleles are different, then they are called heterozygous. One allele is expressed over the other allele. This is called the dominant allele, the unexpressed allele is called recessive. For example, if there was a brown allele and a blue allele, the brown is dominant, so the person would have brown eyes. But not just one pair of genes can control a single trait. Right now there are three known gene pairs that control eye colour. The bey 2 gene on chromosome 15 contains a brown and blue allele. Also on chromosome 15, the bey 1 gene is the central brown gene. On chromosome pair 19 the gey gene contains a green allele and a blue allele.
Complicated!

4. B ~ brown (dominate) b ~ blue (recessive)
PHENOTYPE
(Photo of)
The physical appearance or the result of a given gene
(WHAT IT LOOKS LIKE)
You have brown or blue eyes
ALLELE
Different forms or spellings of a gene
B or b
GENOTYPE
The combination of two Allele inherited
(WHAT ITS GENES LOOK LIKE)
BB, bb, Bb
B ~ brown (dominate) b ~ blue (recessive)

5. Brown eyes Mum & Dad have a baby with Blue eyes?
It depends on what Alleles Mum & Dad have!
GENOTYPE
KS eyes genetics applet
B ~ brown (dominate)
b ~ blue (recessive)

6. Dominant
allele which controls the characteristic whenever it is present.
BB or Bb
recessive
allele whose characteristics only show up when it is present on both chromosomes bb

7. Each organism has two forms of the same gene or Allele, one inherited from mother and one inherited from father
Each Allele is represented by a letter eg T or t for tongue rolling.
Some Alleles have more ‘powerful’ codes than others and are called dominant (eg T) whilst the other type of Alleles is called a recessive (eg t) one. It can be masked by the dominant gene.
If the two chromosomes inherited are the same eg TT or tt, it is homozygous. If the two chromosomes are different eg Tt then it is heterozygous.

8. GENETICS PROBLEMS B ~ Brown b ~ Blue
In humans, blue eyes are recessive to brown:
Dad (Blue eyes)
Mum (Brown eyes)
Baby (Blue eyes) No
Is Mum homozygous for brown eyes? ________
How do you know? (complete the Punnett square)
B b b

9. Example: Tongue rolling gene
Able to roll tongue Allele is Dominate (T)
Unable to roll tongue Allele is Recessive (t)
PHENOTYPE: You can roll your tongue or you cannot
(The Physical appearance of an organism)
TT, Tt, tt
GENOTYPE:
(The Gene order of an organism)
Case study 1
John Tt & Mary tt
Case study 2
Bob TT & Beth Tt
Case study 3
Harry Tt & Jean Tt

10. B ~ brown (dominate) b ~ blue (recessive)
PHENOTYPE
(Photo of)
The physical appearance or the result of a given gene
(WHAT IT LOOKS LIKE)
You have brown or blue eyes
ALLELE
Different forms or spellings of a gene
B or b
GENOTYPE
The combination of two Allele inherited
(WHAT ITS GENES LOOK LIKE)
BB, bb, Bb
B ~ brown (dominate) b ~ blue (recessive)

11. T,t TT, tt Tt, Gg TERMS TO KNOW ALLELES HOMOZYGOUS HETEROZYGOUS
DIFFERENT FORMS OF A TRAIT THAT A GENE MAY HAVE
T,t
HOMOZYGOUS
AN ORGANISM WITH TWO ALLELES THAT ARE THE SAME
TT, tt
HETEROZYGOUS
AN ORGANISM WITH TWO DIFFERENT ALLELES FOR A TRAIT
Tt, Gg

12. T OR G t or g TERMS TO KNOW DOMINANT RECESSIVE
A TRAIT THAT DOMINATES OR COVERS UP THE OTHER FORM OF THE TRAIT
REPRESENTED BY AN UPPERCASE LETTER
T OR G
RECESSIVE
THE TRAIT BEING DOMINATED OR COVERED UP BY THE DOMINATE TRAIT
REPRESENTED BY A LOWER CASE LETTER
t or g

13. MICE A ~ not albino a ~ albino In mice, albino is a recessive trait
Stuart Little
Momma mouse
Poppa mouse
Complete a Punnett square to show how Stuart ended up an albino
If there were 8 babies in the litter, how many would we expect to have normal colouring? _________

14. LABRADORS ? ~ black ? ~ white In Labs, black is the dominant trait
Their pups
are all black
These 2 mate…
What is the genotype of the pups? _____________
The pups grow up and 2 are mated (!?!)
Here are
their kids…
Show how this came about
(draw the Punnett square)
What percentage would we expect to have golden colouring? ____________