1. Pedigrees & Test Crosses

2. POLYGENIC TRAITS Trait is controlled by more than one gene
EX: skin color controlled by more than four different genes
Different combinations of alleles for these genes produce a range of phenotypes.
All heterozygotes are intermediate phenotype

3. Pedigree
Pedigree = graphic representation of genetic inheritance to map genetic traits

8. Autosomal Dominant Trait Requires only one dominant gene
Affected only needs one dominant “M”
What is the genotype of II 2?
Where did he get the dominant M?
What is the genotype of III 4?

9. Autosomal Recessive Trait Requires homozygous recessive
III 4 & 5 must be mm
Their parents both contributed an m
What is the genotype of IV 1?

10. TEST CROSS

11. Test Cross
A test cross occurs when you know an organism’s phenotype (because it has the dominant trait), but not their genotype
In order to determine the organism’s genotype, a test cross is done

12. Procedure for Performing Test Cross
Cross the unknown genotype with a homozygous recessive individual.
Examine offspring.
If all offspring are the same, and have the dominant trait, the unknown genotype is homozygous dominant.
If half (or any) offspring have the recessive trait, the unknown genotype is heterozygous dominant.

13. TEST CROSS Dogs - hereditary deafness caused by a recessive gene “d”
Has a male she wants to use for breeding
The dog can hear - genotype is DD or Dd
If Dd, the owner does not wish to use him for breeding so that the deafness gene will not be passed on.

14. TEST CROSS TEST CROSS = breed the dog to deaf female (dd)
HOMOZYGOUS RECESSIVE
Punnett squares to illustrate two possibilities
In each case, what percentage/how many of the offspring would be expected to be hearing? deaf?

15. TEST CROSS
DD x dd Dd x dd
D d
D D d d d d

16. TEST CROSS
DD x dd Dd x dd
D d
D D d Dd Dd d Dd dd Dd d Dd d Dd dd

17. TEST CROSS DD x dd Dd x dd All offspring Dd or “hearing” D d D D d Dd
Half offspring Dd or “hearing” Half offspring dd or “deaf”
D d
D D d Dd Dd d Dd dd Dd d Dd d Dd dd

18. TEST CROSS How could you tell the genotype of this male dog?
If all offspring hearing = he is DD
If half offspring deaf = he is Dd

19. TEST CROSS
Cross unknown genotype with ____
HOMOZYGOUS RECESSIVE

20. TEST CROSS Tall pea plant - Is is TT or Tt?
Cross with __________________
Do the Punnett squares!
Compare offspring with the Punnett squares
If offspring are 1 tall: 1 short, unknown parent was ______
If offspring are all tall, then the unknown parent was ______

21. Environmental Influences
The genetic make up at fertilization is only the organism’s potential to develop and function
Other factors can influence how gene is expressed or if it is expressed

22. Environmental Influences
External environment – temperature, nutrition, light, chemicals, infection agents
Leaf size, thickness and shape depend on amount of light received

23. Arctic fox coat color depends on temperature

24. Environmental Influences
Internal environment - Hormones  structural differences
horns in sheep are different in male and female
Male pattern baldness
Peacock/peahen feathers
Age can affect gene function