Pedigrees & Test Crosses

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

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

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?

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?

TEST CROSS

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

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.

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.

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?

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

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

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

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

TEST CROSS Cross unknown genotype with ____ HOMOZYGOUS RECESSIVE

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 ______

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

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

Arctic fox coat color depends on temperature

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