Genetics The study of heredity

For generations, people observed that offspring look like their parents Mason Bear and his Dad, Tucker

For generations, people observed that offspring look like their parents, sometimes Silva Bear and her Mom, Sadie

Gregor Mendel Father of Genetics Lived Austrian monk Gardener Had never heard of DNA, genes or chromosomes He had very simple equipment

Gregor Mendel Worked very hard over many years His work with pea plants led us to Mendel’s Laws of Inheritance

What is plant breeding??? In animal breeding, humans decide which animal should be the mom and which should be the dad We can also do this with plants

Mendel’s Results Were Surprising! If you mate a purple flower and a white flower, what do you think the “baby” flowers will look like? How did Mendel explain this???

Punnett Squares Gamete – a sperm (pollen) or egg cell

Each Gene has Two Alleles Each parent contributes one allele A gene is homozygous if it contains two identical alleles A gene is heterozygous if it contains two different alleles

Often, only one allele is expressed The trait is what we see –E.g. Blue eyes, normally shaped hemoglobin, red hair The allele that is expressed as a trait is the dominant allele. The allele that is masked, or not expressed as a trait is the recessive allele.

Mendel Studied Many Traits

Key Terminology Genotype: an individual’s genetic make-up or allele combination (e.g. AA or Aa) Phenotype: an individual’s physical or chemical trait which can be observed –Green eyes –Freckles –Hormone levels –Note: phenotype is often the result of interactions between our genes and our environment

Dihybrid Crosses Genetic cross between individuals differing in 2 traits –A dihybrid cross of 2 heterozygotes results in a 9:3:3:1 phenotype ratio –Each trait maintains its 3:1 phenotype ratio The probability of two traits being inherited together is the product (x) of their individual probabilities.

Summary of Mendel’s Work Genes code for our traits Variations of genes are called alleles (purple vs. white) Genotype- genetic makeup or allele combination (Pp) –If the alleles are the same, the individual is homozygous.(PP or pp) –If the alleles are different, the individual is heterozygous (Pp) Phenotype- observable trait (purple or white)

Sex-Linked Traits Traits coded by genes on the X chromosome –Females have 2 alleles –Males have 1 only –Men are more likely to express recessive sex-linked traits because only 1 recessive allele is required for expression.

A pedigree is a family tree that records and traces the occurrence of a trait in a family.pedigree

Autosomal Dominant Inheritance Usually expressed in every generation Equally expressed among males and females

Autosomal Recessive Inheritance Usually skips generations Equally expressed by both males and females

Recessive Sex-Linked Inheritance Usually skips generations Mostly affects males

What do you think? Problem #1 Sex-Linked Recessive Inheritance

What do you think? Dominant Inheritance

Damaged Chromosomes Even if all chromosomes are present in normal numbers in a cell, changes in chromosome structure may also cause disorders