1. The study of genes and the inheritance of traits
Genetics

2. (double helix comprising genes)
Chromosome Structure
Cell
Replicated chromosome
DNA molecule
(double helix comprising genes)
Individual atoms
Chromatin: a complex of DNA and protein
Histone proteins

3. Chromosomes
Genes are part of chromosomes, which are long strands of a chemical substance called deoxyribonucleic acid (DNA).
So genes are made up of DNA.
Humans have 46 paired chromosomes (2 pairs of 23), with an estimated 20,000 or so genes that are ‘beaded’ along these tightly bundled strands.
As chromosomes come in pairs, there are two copies of each gene in the cell.

4. Gene control of characteristics
All characteristics are controlled by a minimum of 2 genes.
These genes give the characteristic that may show through.
Different genes that control the same feature are called ALLELES

5. Alleles
An Allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.

6. Alleles
Organisms have two alleles for each trait. When the alleles of a pair are heterozygous, one is dominant and the other is recessive.
The dominant allele is expressed and the recessive allele is masked.

7. Dominance and recessive
Some alleles for a feature are able to mask the influence of other gene when they are paired
The WINNING gene is DOMINANT and is represented by a capital letter e.g. H
The masked gene is RECESSIVE shown as lower case of the same letter e.g. h

8. Alleles TT – is dominant Tt – is dominant tt - is recessive
T – is considered a dominant allele
t – is considered a recessive allele
TT – is dominant
Tt – is dominant
tt - is recessive

9. Phenotype They are the traits determined by reading the genotype.
Example : FF = black fur
Black fur is the phenotype or trait

10. Punnett Square
Uses parental genotypes to determine the possible traits of their offspring.
4 offspring

11. Selected Hereditary Traits
Dominant
Recessive
Right handedness
Left handedness
Hair on middle
Segment of digits no hair
Hitch-hiker’s thumb
Normal thumb
Polydactylism (extra digits)
Normal digits
Brachydactylism (short digits)
Pattern baldness
Normal hair
Free ear lobes
Attached ear lobes
Polydactylism is a dominant trait; a normal number of digits is the recessive condition.
In this crowd of men, almost all show some degree of pattern baldness, a dominant trait.
Hitch-hiker’s thumb
Free ear lobe
Attached ear lobe
Handedness
Mid-digit hair

12. Human Handedness Dominant Recessive R r
The trait of left or right handedness is genetically determined.
Right-handed people have the dominant allele.
People that consider themselves ambidextrous can assume they have the dominant allele for this trait.
Dominant
Recessive
Phenotype:
Right-handed
Allele: R
Phenotype:
Left-handed
Allele: r

13. Brown, green, hazel, or grey
Eye Color
Determination of eye color is complex, involving perhaps many genes.
Any eye color other than pure blue is determined by a dominant allele that codes for the production of the pigment called melanin.
Hazel, green, grey and brown eyes are dominant over blue.
Dominant
Recessive
Phenotype:
Brown, green, hazel, or grey
Allele: B
Phenotype:
Blue
Allele: b

14. Human Tongue Roll Dominant Recessive T t
The ability to roll the tongue into a U-shape when viewed from the front is controlled by a dominant allele.
There are rare instances where a person can roll it in the opposite direction (to form an n-shape).
Dominant
Recessive
Phenotype:
Can roll tongue
Allele: T
Phenotype:
Cannot roll tongue
Allele: t

15. Human Mid-Digit Hair
Some people have a dominant allele that causes hair to grow on the middle segment of their fingers.
It may not be present on all fingers, and in some cases may be very fine and hard to see.
Dominant
Recessive
Phenotype:
Hair on mid segment
Allele: M
Phenotype:
No hair on mid segment
Allele: m

16. Thumb Hyperextension Dominant H Recessive h
There is a gene that controls the trait known as hitchhiker's thumb, which is technically termed distal hyperextensibility.
People with the dominant phenotype are able to curve their thumb backwards without assistance, so that it forms an arc shape.
Dominant
Phenotype:
Hitchhikers thumb
Allele: H
Recessive
Phenotype:
Normal thumb
Allele: h

17. Human Ear Lobe Attachment
In people with only the recessive allele (homozygous recessive), ear lobes are attached to the side of the face.
The presence of a dominant allele causes the ear lobe to hang freely.
Dominant
Recessive
Phenotype:
Lobes free
Allele: F
Phenotype:
Lobes attached
Allele: f

18. Other Hereditary Traits
Brown eyes are dominant over blue
Dominant
Recessive
Curly hair
Straight hair
Dark brown hair
All other colors
Coarse body hair
Fine body hair
Syndactylism (webbed digits)
Normal digits
Normal skin pigmentation
Albinism
Brown eyes
Blue or grey eyes
Short or far-sightedness
Normal vision
Normal hearing
Deafness
Normal color vision
Color blindness
Broad lips
Thin lips
Large eyes
Small eyes
Roll tongue into U-shape
No tongue roll
A or B blood factor
O blood factor
Dark brown hair is dominant over other hair colors

19. Your genetic characteristics (phenotype) *Circle the trait you have!
Number of class mates with each trait (or phenotype). Create a tally.
Eye colour
B –brown
b – blue
Brown
*includes any other eye colour other than blue
Blue
Handness
R – right hand
r – left hand
Right
Left
Tounge roll
T – can roll
t – cannot roll
Can roll
Cannot roll
Mid digit hair
M – Hair
m – No Hair
Hair
No Hair
Thumb extension
H – bent
h – normal
Hitchhikers
Normal
Ear Lobes
F – free
f – attached
Free
Attached