What is Genetics?• Genetics: Study of heredity

• Heredity: passing of traits from parent to child

• Patterns of relatedness can help predict offspring characteristics– Autosomal recessive

– Autosomal dominance

– Sex-Linked

– Incomplete dominance

– Codominance

When parents get together…they exchange their genes

The genes combine to create a baby

• “Father of Genetics”• Famous for pea plant

studies• Mendel studied seven

pea plant traits– Color, shape, texture,

height, etc…• Results shaped our

understanding of genetics

Mendel’s 7 traits studied

F1 Generation

P Generation

Mendel crossed a purple and a white flower

The flowers exchanged their genes to make babies

Mendel was shocked! Even though 1 parent was white in color, every flower that was produced was purple!

Was white gone forever?

F2 Generation

F1 Generation

Mendel then took two of the newly created purple flowers and let them reproduce

WOW! White returned! Even though both parents were purple!

Mendel found a 3:1 ratio for flower color. But what about the other traits he examined?

Each trait had a 3:1 ratio. No way that can be a coincidence!

• 1 form of a gene may prevent the expression of the other– Dominant gene hides

recessive gene

• Organisms inherit 2 copies of each gene– One from each parent

Dominant + Dominant Allele

Homozygous Dominant

Recessive + Recessive Allele

Homozygous Recessive

Recessive + Dominant Allele

Heterozygous

Dominant + Recessive Allele

Heterozygous

• Genes are located on chromosomes

• Traits are determined by genes from mom and dad– Allele: Alternative forms of a

gene• Letters used to abbreviate

alleles– Dominant Allele = Capital

letter– Recessive Allele =

Lowercase letter

• Phenotype: Actual appearance of a geneEx: Purple flowers

• Genotype: Genetic makeup of an organismEx: 2 dominant alleles (PP)

• Genotype determines phenotype

Cross a homozygous dominant yellow (YY) plant with a homozygous recessive green (yy) plant

Key

Y = yellow

y = green

Probability of growing a yellow plant? _____________

Probability of growing a homozygous recessive plant? ____________

100%

0%

Probability of growing a homozygous dominant plant? ____________0%

Cross a heterozygous dominant yellow (Yy) plant with a heterozygous dominant yellow (Yy) plant

Key

Y = Yellow

y = green

Probability of growing a heterozygous plant? ________

Probability of growing a green plant? ________

Probability of growing pure yellow? _________

50%

25%

25%

Maria is a heterozygous healthy (Hh) female and Jeff suffers from recessive cystic fibrosis (??).

Key

H = healthy

h = cystic fibrosis

Probability of having a healthy child? _________

Probability of having a homozygous dominant child? ________50% 0%

Kobe Kuiz1) How are dominant alleles expressed? Recessive?2) Which of the following are genotypes? Phenotypes?

TT Green yY Pp Purple gg Smooth3) Which of the following are heterozygous genotypes?

TT Green yY Pp Purple gg Smooth4) Genes may often be found in two forms (dominant and recessive). What are

these alternate forms of a gene called?5) Genes are segments of DNA found on _______________.6) If item A is found in a 2:1 ratio compared to item B, what percentage is item A?7) If item A is found in a 4:1 ratio compared to item B, what percentage is item A?8) George & Martha are planning a family. Each has a family history of autosomal

recessive disorder and they agree to have their blood tested. George is found to be heterozygous healthy and Martha is found to be homozygous dominant healthy. What are the chances they have a healthy child? Homozygous dominant child? Heterozygous child? Homozygous recessive child?